Another human Staph (pseud)intermedius infection

Dr. Stephen Page, a regular supplier of good blog material, sent me a couple papers from the Quarterly Journal of Medicine the other day. One was an interesting report of "Staphylococcus intermedius" infection in a person, entitled "A canine bug in a human heart" (Koci et al, Q J Med 2015;108:337-338).

It’s almost guaranteed that this wasn’t S. intermedius but rather S. pseudintermedius (some medical microbiology labs are apparently still a couple decades behind in identifying this bug). Regardless, it’s an interesting case of a 58-year-old man with a pacemaker that developed fever, chills and a headache. He reported that a neighbour’s dog had licked his hand a few weeks earlier. The pacemaker incision site was unremarkable but "Staphylococcus intermedius" was isolated from two different blood samples. That's a significant concern in a patient like this because of the potential for infection of the heart valves and/or the pacemaker leads. Infections like that can be very serious and hard to eliminate (especially since we know that S. pseudintermedius tends to produce biofilm, which helps it hang around sites like pacemaker leads and avoid antibiotics). Fortunately, after a couple rounds of antibiotics and removal of the pacemaker system, he recovered.

It’s interesting (and encouraging) that the dog exposure was reported. Whether he offered the information or they asked about dog contact isn’t clear, but this is the type of information that’s often missed.

Putting this report into perspective is important. This, and various other reports of S. pseudintermedius infections, show that this dog-associated bacterium can cause disease in people.

But remember:

  • Single cases continue to appear in the medical literature. That means it’s really rare (since a single occurrence is enough to prompt a publication).
  • The relative risk from exposure is limited. Most dogs carry this bacterium and huge numbers of people are exposed every day. So, the incidence of disease with respect to exposure is incredibly low

While "low" is good, it’s not much consolation if you’re the one with the rare but life-threatening infection. So, some basic preventative practices are indicated. Avoiding contact of dog saliva with open wounds would be one. Good general hygiene practices (especially handwashing), avoiding contact with feces and similar common sense measures are probably the key.  Making sure physicians know about animal contact and think about potential zoonotic infections is also important, particularly for people who are at increased risk of infection and disease.

More bad news on the MRSP front

Well, "news" perhaps isn’t the best description since we’ve been seeing it for a while, but a paper in an upcoming edition of the Journal of Clinical Microbiology (Gold et al. 2014) entitled "Amikacin resistance in Staphylococcus pseudintermedius isolated from dogs" provides published support for the trend we’ve been seeing.

Staphylococcus pseudintermedius is an important cause of infections in dogs, and a resistant form, MRSP (methicillin-resistant Staph pseud) is a major problem. MRSP also does a great job of becoming resistant to additional antibiotics, usually by picking up resistance genes from other bacteria. We’ve rapidly lost most of our typical antibiotic treatment options for many MRSP strains, and are left with only a couple of viable drugs. One of those is amikacin, an antibiotic we try not to use when we don’t have to because it has to be injected, and because it can be hard on the kidneys. However, it’s literally a lifesaver in some cases.

Over the past year or two (unsurprisingly, really), we’ve been seeing some amikacin resistance in MRSP strains. I say that’s unsurprising because, with bacteria in general (and MRSP in particular), we’re trapped in a game of "use it and lose it." Any time we use an antibiotic, there is some potential for resistance to develop.

The study by Gold et al looked at 422 Staph pseud from dogs, and found that MRSP were significantly more likely to be amikacin resistant, with a rather astounding 37% amikacin resistance rate in their MRSP collection. Amikacin-resistant strains were also more likely to be resistant to a range of other antibiotics, regardless of their methicillin-resistance.

What do we do?

Tough question. Bacteria eventually seem to outsmart us most of the time (or we seem to "out-dumb" them, since it’s often our poor use of antibiotics that leads to problems).

So, what can be done?

Prevention is better than cure: MRSP infections are almost invariably secondary problems. Preventing or limiting underlying disease (e.g. controlling allergic skin disease) can greatly reduce the number of infections and the amount of antibiotics used to treat them.

Infection control: MRSP surgical site infections are increasingly common, and using good infection control practices should help limit them.

Use them right: Making sure drugs are given as prescribed with proper dosing (amount and frequency), and limiting the use of the few remaining MRSP treatment options for cases that really need them are important.

Antibiotic alternatives: Antibiotics aren’t always needed to treat infections. Topical therapy with things like chlorhexidine shampoo can be highly effective for skin infections, and can save antibiotics for infections that can't be treated otherwise.

Will these steps stop the scourge of antibiotic resistance?

No. But they might buy us some more time to figure out how to better handle this and to save some of our limited remaining antibiotic options.

Superbugs and import control

Issues about infectious disease risks from the pretty much totally unregulated importation of dogs continue to rise, and I’m dealing with them in one way or another almost daily at the moment. I’ll stay away from the discussion of what we are and aren’t (mostly the latter) doing in Canada, since I've covered that before.

What I want to write about now is a push in New Zealand to ban entry of dogs carrying methicillin-resistant (MR) staphylococci, including MRSA and MRSP.

The push makes sense at some levels:

  • MR staph infections are a problem
  • MR staph are currently rare in pets in New Zealand
  • We can find the same strains of MR staph in animals multiple countries, suggesting they do travel from place to place
  • Prevention is better than treatment

However, it’s not that clear cut. One issue relates to the standard line “all staph are not created alike”. Methicillin-resistance is common in a wide range of staph species carried by perfectly healthy animals. Many of those species are of little to no risk to people or animals.

A related issue is how MR staph get into a dog population. There are a few main ways. One is from humans - MRSA and other MR-staph are present in people, and most MRSA in pets is human-associated. So unless there’s a parallel extermination of these bugs in humans in New Zealand (a rather unlikely scenario), there’s an ongoing risk of exposure of native dogs.

Another snag is transmission of methicillin-resistance from common resident staph species to species that cause disease. While MR-staph infections may be very rarely identified in the country, it’s very unlikely that there are no MR-staph of any sort in New Zealand. I’d wager that I could find MR-staph of various sorts in New Zealand dogs, so this risk would remain even if dogs being imported were restricted.

Feasibility and practicality are other concerns. Yes, dogs could be tested and held at the border or in a quarantine facility awaiting results, but what would be tested, and how? How the testing is performed (e.g. what samples are collected and what lab methods are used) can have a major impact on the results. We don’t actually know how to confidently declare a dog to be free of MR-staph. If I had to make a recommendation now, it would be to take swabs of the nose, throat, rectum, skin and area around the hind end (perineum), and test each swab using an enrichment culture method. Since the two main staph of concern, MRSP and MRSA, behave differently in the lab, two different approaches would be required. Further, I wouldn’t have complete confidence in one round of testing, so I would probably want that done at least twice. It's possible but it wouldn't be cheap or easy… and you still won't get me to sign anything saying this will "guarantee" that a dog is free of MR-staph.

Ultimately, trying to prevent entry of MR-staph is rather futile, and it also doesn’t address the bigger issues, such as how antibiotics are used, infection control practices and other components of veterinary care that influence the spread of MR-staph. While I applaud the fact that they’re being proactive by thinking about ways to control these bugs, and that they're paying attention to importation, import controls aren’t going to be a great tool for MR-staph control. Paying attention to judicious use of antibiotics, use of common-sense hygiene practices in households, improvement in infection control practices in veterinary hospitals, and good basic veterinary care for pets would be much more effective.

The big gun antibiotic controversy

I'm getting ready for next week's ASM/ESCMID conference on methicillin-resistant staphylococci in animals, for which I'm involved in a plenary session about critically important antibiotics in companion animals. The whole area of antibiotics and animals in complex and controversial (and made worse by political agendas, lack of evidence and confusion about different issues).

Anyway, one thing that often gets overlooked is the difference between companion animals and food animals in how antibiotics are used, what regulations are in place, and what differences should be present between species. Just discussing antibiotics "in animals" isn't adequate, because a pet dog is very different from a feedlot steer in many respects, and many of the issues around antimicrobial use are different as well.

One question that's going to be up for debate is "should antibiotics that are used in serious resistant infections in people be used in animals?"

My answer to this important question has evolved a bit over the years. It's "yes, but..."

The but is the important part.

  • As a veterinary clinician, I see the need to treat my patients (or the patients I'm providing advice on).
  • As someone who works in the field of antimicrobial resistance, I see the issues with drug use and resistance.
  • As a parent, I don't want my kids to develop a serious infection that I may have played a role in fostering.
  • As a pet owner, I understand the desire to try to save the life of a pet.

That doesn't even cover all the issues, but it shows the variety of standpoints that need to be considered.

Back to the question at hand.  As I said, my answer is yes, but with disclaimers:

  • We need to use antimicrobials only when required.
  • We need to use antimicrobials properly.
  • We need to take measures to reduce infections overall (so that less antimicrobial use is required).

At our veterinary teaching hospital, we have a restriction policy for vancomycin, an important human drug. For it to be used in an animal, the following criteria must be met:

  • The offending bacterium must be susceptible to vancomycin (duh!).
  • There must be no other reasonable antibiotic options that are likely to work.
  • There must be a reasonable chance of survival with treatment.
  • Systemic treatment of the infection is needed (i.e. it can't just be treated with local therapy).
  • The clinician must get approval from infection control (i.e. me).

That has happened twice in the past 12 years. Both cases were dogs with life-threatening abdominal infections; they were each treated with a short course of vancomycin and survived.

That's probably 10-14 days of vancomycin use per ~200 000 patients. I don't know what the comparable numbers would be for people in Guelph General Hospital down the road, but their use would be staggering compared to ours. Also, the risk of resistance with each use is presumably much higher for each human patient since they are in an environment where vancomycin resistant bugs are present (and therefore can be selected for with treatment). Vancomycin resistance is exceedingly rare in our hospital population, further decreasing the risk.

Is there some risk? Certainly. Use inevitably carries some risk.

Does our 2 / 200 000 use constitute a reasonable human health risk? I can't see how it does.

So, is antibiotic use in animals something we can just ignore? Absolutely not. It's a big problem, just like antibiotic use in people. However, just as all animal species issues aren't the same, all types of antibiotic use aren't the same.

Are there other things we can focus on to reduce resistance? Absolutely.

  • A 1% improvement (i.e. decrease) in use of fluoroquinolones in animals would probably have a dramatically greater effect on resistance in human and animal pathogens than a complete ban on vancomycin. Fluoroquuinolones are a commonly used drug class in animals that is also important in people, and one in which resistance is certainly an issue.
  • A 1% improvement (i.e. decrease) in use of of fluoroquinolones in humans would probably have an even greater effect.
  • Better infection control, preventive medicine and other practices could potentially have an even greater impact by reducing infections and therefore the need for any drug therapy, and delaying the treat-resistance-more treatment-more resistance cascade.

Some people would say that any drug that's of any relevance in humans should not be used in animals. Some veterinarians would say no one should control their prescribing practices. Like most things, I think there's a happy (and more effective and practical) middle ground. It's not the status quo, though. We need to have discussions about how to control antimicrobial use in all species, including humans, and not just pointing fingers at the other side.  We also need to discuss how to improve infection control to reduce the need for antimicrobials, and how to improve the way we use antimicrobials when they are required.  In order to have good discussions, we also need proper data (something that's still lacking).

Different opinion? Feel free to comment (or show up in Copenhagen next week).

Should a dog with MRSP be spayed?

This is an increasingly common question, as methicillin-resistant Staphylococcus pseudintermedius (MRSP - essentially the canine version of the high-profile human "superbug" MRSA) has expanded greatly in the canine population. As more dogs get MRSP infections and even more become inapparent carriers of this bug, more dogs that are carriers will need surgery (both elective and non-elective).  Since MRSP is now a leading cause of surgical site infections in dogs, there's concern about what to do with these carriers, particularly when it comes to elective surgeries like spays and neuters.

My answer to the question is... maybe.

If the dog has an active MRSP infection (e.g. skin infection), I'd say "hold off for a while" if possible. I don't like elective surgeries being done on animals with active infections (this applies to almost any kind of infection, not just MRSP). If an animal has an active MRSP infection, it might increase the risk of the surgical site becoming infected because of the greater overall burden of MRSP on the skin and elsewhere.

If the dog doesn't have an active infection (e.g. is a healthy carrier after having gotten over a previous MRSP infection), I'd say "go ahead."

Here's why:

  • Spay-associated infections are quite rare.
  • We don't use antibiotics prophylactically (i.e preventatively) for spays (or at least, they shouldn't be used for this kind of low-risk procedure - unfortunately some people still use them inappropriately).
  • MRSP is no more likely to cause a spay infection than methicillin-susceptible S. pseudintermedius. It's just harder to kill when an infection occurs.
  • Methicillin-susceptible S. pseudintermedius can be found on almost all dogs.

So, if infections are rare, despite the fact that S. pseudintermedius is present on pretty much all dogs and that we don't use drugs to kill S. pseudintermedius during (or after) spays, there should be no added risk of infection by the antibiotic-resistant version of this bug.

Every dog is carrying lots of different bacteria that can cause an infection at any time. That's why we use a variety of surgical antisepsis practices (e.g. clipping, scrubbing, sterile instruments, proper operating room) to help prevent a critical number of bacteria from getting into the sterile surgical site where they can start to cause problems.

This strategy doesn't necessarily apply to surgeries where antibiotics are used prophylactically and where staph are the main causes of infection, especially in situations like orthopedic procedures where MRSP infections are common and can be very hard to treat. What to do in those cases with an MRSP-positive animal is a tougher question, and we're working on an answer to it at the moment.

Shelter dog MRSA panic

Several dogs at a Miami humane society were quarantined last week because of concerns (or possibly panic/over-reaction) about methicillin-resistant Staphylococcus aureus (MRSA). MRSA in dogs is a concern because it's an important cause of infection in both people and animals. However, it's an opportunist, meaning it typically doesn't cause disease when it encounters a normal, healthy person or animal. In fact, a small percentage (~1-3% probably) of the human and pet populations carry this bacterium in their nose without knowing it, and the vast majority never suffer any consequences.

It's often tough to strike the right balance when dealing with an MRSA issue. We want people to realize that it's an important cause of disease and that it needs to be taken seriously, but we also want people to keep it in perspective and not freak out.

The Miami shelter report seems to be on the "freak out" side, particularly on the part of the local media.

It's not really clear what's happening based on this fairly poor article. The shelter's Chief Medical Officer, Dr. Maureen Swan, is quoted as saying there's a routine respiratory disease cluster in the shelter, but MRSA rarely causes respiratory disease in dogs. The article then adds Dr. Swan said it was "not the highly contagious MRSA virus." I have no idea what that means, and MRSA is not a virus.

My suspicion is that they have respiratory disease caused by the typical bacterial and/or viral pathogens that are commonly found in shelter dogs, and that they isolated a methicillin-resistant staph that just happened to be hanging around in that particular dog (since such bacteria normally live in the mouth, nose and skin). It's also not really clear whether this is MRSA. The article says MRSA, but the first thing I ask when I get an advice call about MRSA is "what staph species does the report say was isolated?". Most often, it's Staphylococcus pseudintermedius or another staph. These bugs can still be relevant, but they don't carry the same human health risk as MRSA, so it's important to know exactly what's been found.

Finding MR staph, including MRSA, isn't unheard of in a shelter. It's just one of many reasons that good general infection control practices are needed in these facilities. When MRSA is found, taking some extra precautions is reasonable because of the potential for disease and transmission to people, but too often people panic. It's understandable based on concern about MRSA and the scary stories people can find with a quick Google search. Not uncommonly, there's a combination of an short-term overly aggressive response while at the same time failing to improve basic infection control practices, which are the most important.

More information about MRSA can be found on the Worms & Germs Resources - Pets page.

Methicillin-resistant staph in animals meeting

Is MRSP in a dog a risk to the family?

This is an increasingly common question, because MRSP is increasingly common. I've had two calls about it this week, and it's only Wednesday.

It's a good question to ask because MRSP (methicillin-resistant Staphylococcus pseudintermedius) is a highly drug-resistant bacterium that causes a lot of problems in dogs, and because of the high profile of its relatively distant relative, MRSA (methicillin-resistant Staphylococcus aureus), in people.

The short answer is: Yes, MRSP can infect people

BUT... (and it's a big and important but):

It's exceedingly rare and the overall risk is very low.

Here's my reasoning behind this answer:

1) Reports of MRSP infections in people are very rare.

  • I think there are only two such published reports at the moment. There have probably been more infections than the number that are published, and there's the potential for MRSP to be misdiagnosed by some human diagnostic labs (meaning some MRSP infections may be mistaken for something else), but I think it's fair to sayl this a very rare infection in humans.

2) MRSP is not well adapted to infect people.

  • MRSP is not inherently any more likely to cause infection than methicillin-susceptible strains of S. pseudintermedius (MSSP).
  • MSSP can be found on basically every dog.
  • A large percentage of the human population has contact with dogs every day.
  • So, a large percentage of people encounter MSSP every day. Yet, reports of MSSP infection in people are very rare. To me, that indicates that this bacterium is poorly adapted to be a human pathogen.

3) Veterinary dermatologists are not extinct.

  • MRSP is very common in dogs with skin infections. In some practices, it's the main cause of these infections.
  • That means veterinary dermatologists encounter a lot of MRSP every day.
  • I have yet to hear a report of a veterinary dermatologist getting an MRSP infection (carriers yes, disease no). I wouldn't be surprised if there actually have been some infections, but dermatologists can be considered the canaries in the mine when it comes to human MRSP risk, and I'm not aware of any real issues.

4) All dogs are biohazardous

  • While this may not comfort the people calling me who are worried about the health of their families, it's important to put things into perspective. All dogs are carrying multiple microorganisms that could cause disease in people under the right circumstances (and the same goes for all cats, horses, people etc. for that matter).
  • If you screened the average dog, you'd find things that are of greater concern that MRSP. In fact, MRSP probably barely cracks my "Top 10 List" of things I'm worried about the average dog spreading.

So, yes, there's a risk of MRSP infection when a person has contact with a dog infected with or carrying MRSP. There's also a risk of infection from methicillin-susceptible S. pseudintermedius, the version of the bug that basically all dogs carry, and a whole range of other bugs.

There will never be a zero-risk pet when it comes to zoonotic diseases. It's impossible. The risks may be very low but we can never eliminate all risk, just like we can never eliminate all risk from walking down the street. For some people, that slight degree of uncontrollable risk might be too much to handle, and they probably shouldn't own a pet. For most, the positive aspects of pet ownership outweigh the risks, and some basic hygiene practices (e.g. handwashing, avoiding licking, avoiding contact with the dog's mouth, nose and bum) can reduce that already low risk even further.

MRSP infection in a person

Is MRSP zoonotic?” That’s a question I get all the time. MRSP (methicillin-resistant Staphylococcus pseudintermedius) is a canine staph (a bacterium) to which people are exposed all the time. Yes, it can infect people, but only very rarely, particularly when you consider how often they’re exposed. Nonetheless, human MRSP infections can occur.

My typical answer to the question is “Yes, but…” followed by an explanation of the overall low risk. My general line is:

  • It can be transmitted to people.
  • Human infections are very rare
  • There’s no use panicking over MRSP or being draconian when you have an infected animal.
  • At the same time, no one wants a highly resistant infection, so some basic measures should be used to reduce the risk of transmission.

Issues are also greater when people with compromised immune systems are involved, and a recent paper highlights this.

The paper (Savini et al, Journal of Clinical Microbiology 2013) describes MRSP infection in a 65-year-old man who was immunocompromised because of a bone marrow transplant. He developed a wound infection, and his physicians and the diagnostic lab did a pretty comprehensive study of the bacterium they isolated from the wound, ultimately determining it to be MRSP.

The man lived “close to a pet dog and farm cows," whatever that means. The dog was probably the source, but unfortunately (as is common) no efforts were made to see if the dog was carrying MRSP, to see if the cows were positive for MRSP (since this bug can rarely be found in cattle), or to type the isolate to see how it compares to strains that are typically found in animals.

Will this report change my answer to the first question? No. It gives me another example of a human MRSP infection, but such events are still exceedingly rare and this individual was highly immunocompromised, having graft-vs-host disease after his bone marrow transplant.

We don’t need to be afraid of MRSP, but we need to realize there is some risk, and the risk is presumably higher for certain people (e.g. very young, very old, people with compromised immune systems). We therefore need to use some basic infection control and hygiene practices to reduce the incidence of transmission of MRSP and other potentially harmful microorganisms from animals to people.

More information about MRSP can be found on the Worms & Germs Resources - Pets page.

Equine MRSA in Israel - Different strain, same old tricks

It's been quite a while since the last post about MRSA in horses, but rest assured, it's still out there!  Not too surprisingly it's also spreading (or at least starting to be found) in new places.  A recent report in Veterinary Microbiology (Schwaber et al, 2013) describes an MRSA outbreak at a large animal teaching hospital in Israel.  It is the first report of MRSA colonization in horses in the Middle East, although it's possible (and quite likely) that there's more to be found.

The discovery of the problem had a pretty typical progression: there were two horses in the hospital with post-operative wound infections from which Staphylococcus aureus was cultured, and the isolates from both horses had similar antimicrobial resistance patterns, including resistance to all beta-lactam antimicrobials (= MRSA). Validly concerned about the potential for the MRSA to spread among horses and people in the hospital, an investigation ensued - in this case the National Center for Infection Control (NCIC) was actually called in to coordinate the operation.

  • They found MRSA in 12/84 (14.3%) horses, of which 11 were in the hospital at the time of sampling, and 1 had recently been discharged from the hospital.  Consider though that 44 of the horses sampled were simply from farms from which an MRSA-positive horse had come - so 11/40 horses in the hospital were positive - that's 27.5%!
  • 16/139 (11.5%) of personnel at the teaching hospital were positive for MRSA.  Fortunately there were no clinical MRSA infections reported in people.
  • The MRSA strain that was found in all the horses and most of the people was a very rare type - not the usual sequence type 8 (ST8) we're used to finding in horses in various other parts of the world.  This one was an ST5, spa-type t535, SCCmec type V, which is even rare in the human population.
  • The primary action taken to get the outbreak under control: increased infection control measures, including isolation of infected and colonized horses which were then handled with contact precautions (e.g. gloves, gowns), discharging horses from hospital as soon as medically possible to decrease transmission pressure, and having a nurse from the NCIC come in to instruct personnel on the measures to be taken, including emphasis on hand hygiene and increased use of alcohol-based hand sanitizer.
  • In this outbreak, decolonization therapy was prescribed for all colonized personnel.

The report does not mention whether or not personnel at the hospital were required to submit to being tested and undergoing decolonization therapy.  This can be a very tricky issue to handle, and it depends on what the local laws are.  In Canada, employees cannot be forced to undergo testing or treatment, but in some other countries MRSA-positive healthcare workers may not be allowed to even work until their carrier status is cleared.

Interestingly enough, just a year or two before this outbreak occurred a study (as yet unpublished) had been carried out in the same region, during which they found MRSA in 7.2% (6/83) of hospitalized horses and none in horses from local farms.  There is no mention regarding whether or not the hospital had taken measures to eradicate MRSA from the facility before the clinical infections that triggered the outbreak investigation occurred.

This was a typical MRSA "iceberg" - a couple of clinical cases were triggers for an investigation that found a lot more horses and people were actually carriers.  This is exactly why it's important to remain diligent about infection control measures like hand hygiene at all times, so that pathogens like MRSA don't move in "under the radar."  The authors of the paper summed it up nicely (although I'd leave out the part about decolonization):

"Strict implementation of hand hygiene, isolation of colonized and infected horses, decolonization
of colonized personnel and above all, constant education of veterinary students and personnel about the importance of infection control measures are required in order to decrease the risk for colonization and infection of both horses and personnel by MRSA and other pathogens."

More information about MRSA in horses is available on the Worms & Germs Resource - Horses page.

Do you know what's in your dog's 'bully stick'?

I mean that two ways.

1) Do you know what a bully stick actually is?

2) Do you know what's in it?

A recent study headed up by Dr. Lisa Freeman, published in this month's Canadian Veterinary Journal (Freeman et al., CVJ 2013;54:50-54), looked into this by asking people what they thought bully sticks were made of, and testing the treats for calorie count and bacterial contamination.

The answer to question 1 is: bully sticks are raw, dried bull penis (which explains the need for a cuter name).

  • Only 44% of people surveyed knew that.

Also, bull penis is considered a by-product, yet 71% of people that fed bully sticks to their dogs said they avoid by-products in food.

  • This just shows a lack of understanding about what by-products are and their nutritional value. Many people classified things that are prohibited from by-products as being by-products, such as hooves, horns, road kill and euthanized pets. By-products aren't always bad and can, in fact, have good nutritional value. Also, they can be environmentally friendly and ethical since they are often made from nutritionally valuable parts of the animal that might otherwise be thrown out, thereby providing food for pets without taking anything out of the human food supply chain.

"What's in it?" was approached from 2 standpoints:

Firstly, caloric content was assessed.

  • Treats often get ignored when thinking about a pet's caloric intake, but calorie-dense treats can certainly contribute to obesity. Fifty percent of people surveyed underestimated the calorie counts of bully sticks. The average caloric density was 3 calories/gram, and given the variation in size of bully sticks, total calorie counts for a single stick ranged from 45-133 calories (9-22 calories/inch). So, yes, size matters.

Secondly (my bit part in this study), we looked at contamination by a select group of bacteria.

  • Salmonella wasn't found, which was encouraging since high Salmonella contamination rates have previously been found in some treats (mainly pig ears), and contact with pet treats has been implicated in some outbreaks of salmonellosis in people. We found Clostridium difficile in 1 treat (4% overall). That doesn't worry me too much since it's increasingly clear that we encounter this bacterium regularly. With common sense and handwashing, it's probably of little risk, but in some people (e.g. elderly, people on antibiotics, people with compromised immune systems) it might be more of a concern. We also found methicillin-resistant Staphylococcus aureus (MRSA) in one sample. This was a "livestock-associated" MRSA strain that can cause infections in people, but the risk is unclear. Theoretically, it's a potential source of exposure. If someone got MRSA on their hands from the treat then touched their nose (where MRSA likes to live) or a skin lesion (where it can cause an infection), then it could potentially cause a problem. Overall, the risk is probably quite low, but it's another reason to wash your hands after handling treats.

None of this means dog owners need to avoid bully sticks. It does mean that you should pay attention to what you feed your pet, think about treats when considering your pet's caloric intake (especially if your dog is overweight), keep treats away from high risk people (e.g. don't use a bully stick as a teething toy) and wash your hands after handling dog treats (of any kind).

Photo: A variety of bully sticks (also known as pizzle treats) often fed to dogs as chew treats (photo credit: Gergely Vaas 2006 (click for source))

MRSA in an alpaca

Following up on my recent post about MRSP in rats, here’s a story about MRSA in an alpaca (Stull et al, Can Vet J 2012). As far as we know, it’s the first report of MRSA in an alpaca (or any camelid).

The report relates to our large animal hospital, where we perform MRSA screening of all horses at admission, weekly during hospitalization and at the time of discharge. It's all part of our infection control program, and the screening is designed to help reduce the risk to horses and our hospital personnel, since this multidrug-resistant bacterium is endemic in the Ontario (and broader) horse population, and outbreaks can occur in equine hospitals.

While alpaca’s aren’t horses, and we don’t see that many of them here, they sometimes get screened anyway since screening is being done on most of the other patients.

This case involved a neonatal alpaca that was admitted with its mother because of severe respiratory disease. The cria (baby alpaca) was very sick and was ultimately euthanized about 36 hours after admission.

Surprisingly, the admission MRSA sample from the cria was positive. In this case, MRSA wasn’t involved in the animal's illness. The cria didn’t have any evidence of bacterial infection, so this was an incidental (but interesting) finding.

When the bacterium was tested further, it was classified as CMRSA-5 (Canadian epidemic MRSA-5), a human strain that also predominates in horses in North America. The mother alpaca was MRSA negative. Presumably, the cria picked up MRSA from the farm environment or a person shortly after birth. MRSA (especially CMRSA-5) carriage rates are high amongst horse owners and horse vets compared to the general public, and it would have been nice to have determined if there were any horses on the alpaca’s home farm, but we couldn’t get any follow-up information.

This single case is probably of limited concern in the grand scheme of things. It’s likely an "oddball" infection rather than an indication that MRSA is a serious threat to alpacas, or that alpacas are a relevant source of human MRSA infection. However, that’s largely what was said when MRSA was first found in horses in the late 1990's and early 2000's, and it has since become a significant issue in that species, so the potential for MRSA to become a problem in alpacas can’t be completely dismissed.

If nothing else, the occurrence of this case is an indication of the need think broadly when it comes to infectious diseases, since many pathogens don’t have species boundaries. CMRSA-5 is a human-origin MRSA strain, but it’s worked its way outside of its natural host. It’s not the first and certainly won't be the last bug to make its way from people to animals.


MRSP in urban rats

A year or two ago, I received an email from Dr. Chelsea Himsworth, who was doing some interesting work looking at different bacteria found in rats in Vancouver's Downtown Eastside. This is an impoverished urban neighbourhood with lots of homeless people, IV drug users and HIV-infected individuals... and lots of rats. Dr. Himsworth, a veterinary pathologist working on a PhD at the University of British Columbia, is assessing potential health risks posed by rats to this type of population. The reason she got ahold of me was to see if I was interested in looking for some different bacteria, like methicillin-resistant staphylococci, in these rodents.

If you look, you often find, and that was the case here with methicillin-resistant Staphylococcus pseudintermedius (MRSP). This multidrug resistant bacterium was found in nasal or oral swabs from 2.1% of rats (Himsworth et al, Emerging Infectious Diseases 2013). So it was relatively uncommon but certainly present.

One question: from where did it come? Most MRSP isolates found were the same as the most common strain found in dogs, so presumably the rats picked it up directly or indirectly from pets or stray dogs. However, there was also a type we've never run across before. That could mean that there is a separate rat-associated MRSP strain, but more likely it means this strain is present in dogs in Vancouver and we just haven't found in dogs elsewhere yet (there aren't many of us typing MRSP, and we find new strains not uncommonly). While dogs and rats presumably don't spend time lounging around together, there is certainly potential for direct or indirect contact between dogs and rats, and rats have been found to harbour dog-associated oral bacteria in the past.

Another question: what's the risk to people? The risk of infection is probably limited, but not zero. MRSP can cause infections in people but doesn't do so very often. MRSP is unfortunately becoming fairly common in dogs, so people are commonly exposed, yet human infections are still rarely diagnosed. So, the risk to humans from these rats carrying MRSP is pretty low overall, although we'd rather not see new reservoirs for this bug.

What about the rats? Rats may be the innocent bystander here, having been infected by dogs. We don't know whether MRSP causes infections in rats. It probably can in certain circumstances.

Can rats spread this to dogs? I guess it's possible. Rats are probably not contaminating the environment too heavily with this bug from their noses or mouths (compared to dogs), but direct transmission if a dog caught a carrier rat could certainly be possible. The risk to the dog population is pretty low since this pathogen is well established in dogs already and there's a lot more dog-dog than rat-dog contact.

Why does an antibiotic-resistant bacterium live in these rats when they're not receiving antibiotics? Good question. Antibiotics certainly help when it comes to selecting for resistant bacteria, but they're not absolutely required. There are a lot of other factors that can also play a role, so rats don't need direct or indirect exposure to antibiotics to acquire MRSP (or other multidrug-resistant bacteria). It could be that they are just commonly exposed and the bacterium only hangs around for a short period of time, or that there are some other factors in the rats, their food or their environment that select for these resistant bacteria.

Staph 'intermedius' infections from dogs

When I give talks about methicillin-resistant staphylococci, I almost invariable get into a discussion of the risks of methicillin-resistant S. pseudintermedius (MRSP) in people. This bug is becoming increasingly common in dogs and because it's so resistant to antibiotics, there's concern about whether it can be transmitted to people.

My usual answer is that there is a low risk of MRSP infection in people, but not no risk. MRSP is no more likely to cause an infection in a person compared to it's antibiotic-susceptible counterpart, regular S. pseudintermedius (the resistant version is just harder to treat). Most dogs carry susceptible S. pseudintermedius in their mouths, nose, skin, ears and/or intestinal tracts, so people in contact with dogs are very commonly exposed. Yet, human infections seem to be quite rare. There are periodic reports in the medical literature about S. pseudintermedius infections in people, but they tend to be single case reports, and when someone can publish a report of a single infection in person, you know it's pretty uncommon (since if it was common, no journal would be interested).

That's my long-winded way of introducing a recent case report in the Journal of Clinical Microbiology (Hatch et al. 2012). The patient in the report was an elderly man with underlying disease, so someone who was at high risk of infection from bugs that don't often affect otherwise healthy people. He had skin lesions, sore joints and a bloodstream infection, and "S. intermedius" (I'll get to the name issue later) was isolated from his blood. Fortunately, he was successfully treated. He owned a dog and that was (reasonably) considered to be the source of the bacterium, but no testing was done to look into that. So, from a disease standpoint, it's not really a surprising case - just another in a series of very rare infections that have happened.

The other issue here is the fact that the authors (along with the diagnostic lab, the journal's reviewers and the editor) are behind the times and don't realize that it's virtually guaranteed that this person didn't have a S. intermedius infection. Rather, it was presumably S. pseudintermedius, or perhaps another similar staphylococcus. It wouldn't have much of an impact on this particular case, although not knowing the species probably also indicates the lab doesn't know that there are different breakpoints to determine if the bug is methicllin-resistant, and there's the potential they would miss methcillin-resistant S. pseudintermedius and use an inappropriate and ineffective treatment (fortunately that didn't happen here).

Essential oils...the overlooked MRSA "solution"?

Methicillin-resistant Staphylococcus aureus (MRSA) and other antibiotic-resistant bacteria are big problems. They account for millions of illnesses, thousands of deaths and billions of dollars in costs every year internationally. Antibiotic-resistance is a complex issue, but some people try to over-simplify (and under-analyse) the problem.

A recent article on is an example. Entitled "MRSA cases double in five years while natural solution is overlooked", the article - while providing very little real information - claims that essential oils are "unmatched tools in the fight against MRSA."

  • It talks about the bacterial killing power of essential oils. That's certainly true. Many essential oils are potent antibacterial substances.
  • It also claims that essential oils are "free of the side-effects common to antibiotics." That's not so true. In fact, essential oils can be quite toxic. Tea tree oil, one of the more popular essential oils, can cause a range of adverse effects, and I'm aware of a couple of dogs that have died from suspected tea tree oil toxicity. A study presented at the North American Dermatology Forum last fall (Valentine et al.) showed that while some essential oils were effective against resistant staphylococci, they also had damaging effects on canine skin cells. One oil had essentially no antibacterial effect but did a lot of damage to skin cells.

The antibacterial effects of essential oils might be useful, but only if they do no damage to the animal (or person) at the same time. The problem is these products are not technically sold as drugs, despite the fact that they are really marketed as drugs, so they bypass the requirement to demonstrate safety and effectiveness. If a product showed good antibacterial activity and no toxicity, it would be a potential option for the treatment of superficial infections, but in the absence of proper testing demonstrating safety, I wouldn't use an essential oil, as it may do more harm than good.

The article doesn't contain much useful information and is more of an infomercial than anything else. It highlights on particular company called Young Living Essential Oils. The author of the article also seems to be that company's "Product Training Program Manager," according to articles he's also written on the website. No conflict of interest there, obviously!

A complex problem like antimicrobial resistance requires complex solutions. Non-antimicrobial options are one part of this, which is why my lab has done work in this area. However, all-natural doesn't necessarily mean safe or effective, and we need to demand proper testing of such products. Too many companies take the cheap and easy way out and don't do any testing. While they may make money, their customers (and their pets) are the ones who can end up paying the price.

Was ist MRSP?

Since MRSP is an international problem (no matter what language you speak), there is now a resource sheet for our German-speaking friends as well:

Informationen in Deutsch ist ab sofort verfügbar hier und in unserem Abschnitt Ressourcen. Ubersetzt von Georg Lehner, Dr. med. vet.


Methicillin-resistant staph...What's in a name?

I've written about this topic before, but it's an important (and increasingly common) issue to understand, so bear with me while I address the subject again.

I typically get multiple case consults in person, by phone or by email about methicillin-resistant (MR) staphylococci every day. A lot of these start with "I have a case with an MRSA infection..." While trying not to be rude, I tend to interrupt the conversation at that point with "Is this actually Staph aureus or another staph?"

I do this for a few reasons:

  • A few years ago, the vast majority of "MRSA" infections in dogs, cats, horses and other companion animals were actually MRSA - that is methicillin-resistant Staphylococcus aureus. However, in the past few years, there's been a tremendous upsurge in other MR-staph, particularly booming numbers of MR-Staphylococcus pseudintermedius (MRSP) infections in dogs. These days, if it's a dog or cat, when I ask the "What staph is it?" question it's usually not actually MRSA. We're  starting to see more MRSP in horses too, complicating things in that species as well.
  • Staph are divided into two groups, coagulase positive species (which include S. aureus and S. pseudintermedius) and coagulase negative species. The coagulase negative species are commonly found in or on healthy animals and are often methicillin-resistant, but they are not very virulent and don't usually cause disease outside of very high risk populations (e.g. very sick animals in a veterinary hospital). If a MR coag-negative staph is isolated, I am far from convinced it's the culprit, and typically the real cause of the problem still needs to be found.
  • MRSA is much more of a concern from a public health standpoint, as it can move between animals and people. While MRSP can cause human infections, these are extremely rare.
  • MRSA is not really adapted to live in dogs, cats, horses and many other animals. It can, for a while, but doesn't do so longterm, and the vast majority of MRSA carriers will get rid of it on their own. In contrast, it appears that MRSP (at least in dogs) can stay with the animal for a very long period of time. Therefore, an animal that has had an MRSP infection has a reasonable chance of shedding the bacterium for a long period of time, which might be of relevance for its health in the future.
  • The two main MR-staph of concern in companion animals are MRSA and MRSP. Some diagnostic labs still don't try to differentiate the two, despite the fact that there are different guidelines for determining whether they are methicillin-resistant. If someone has a result that doesn't differentiate MRSA from other staph, I tell them their lab isn't doing things right and they need to talk to them so they can have confidence in the results.

More information about MRSA and MRSP can be found on the Worms & Germs Resources page.

More on MRSA and meat

While it shouldn't come as a surprise considering other studies, a recent study in PLoS One (O'Brien et al 2012) has caused a bit of a stir in the US. This study, headed up by Dr. Tara Smith's research group in Iowa, looked for methicillin-resistant Staphylococcus aureus (MRSA) in retail pork. They bought pork from different stores in Iowa, Minnesota and New Jersey, and tested it for the presence of MRSA. They focused on pork because MRSA can be found widely in pigs internationally, including in the US.

Not surprisingly, they found MRSA. Overall, they tested 395 pork samples from 36 stores, including both "conventional" pork (300 samples) and "alternative" pork (95 samples). The latter consisted of samples labelled "raised without antibiotics" or "raised without antibiotic growth promotants." MRSA was found in 6.6% of samples; 6.3% of conventional pork samples and 7.4% of alternative pork samples.

When they looked at the MRSA types that were present, 27% were the ST398 "livestock-associated" MRSA that's most commonly found in pigs.  However, like our earlier Canadian studies, they found common "human-associated" MRSA strains more often. These strains can also be found in pigs, albeit less commonly than ST398, and it's unclear whether meat contamination with these strains comes from pigs or from people who handle the meat throughout the processing chain.

The fact that there was no difference between conventional and antibiotic-free pork isn't surprising to me, although it catches some people off-guard because of some basic over-assumptions about the relationship between antibiotics and MRSA in food animals. We can find MRSA quite commonly on both regular and antibiotic-free farms.  While it's reasonable to assume that antibiotics were a key factor in driving the emergence of MRSA in pigs, there's not much evidence showing that ongoing antibiotic use is an important factor in determining whether MRSA is present on specific farms or in specific pigs. One potential explanation is that in order to control infections, farms that stop using antibiotics start using other substances such as zinc in feed to help control overgrowth of certain intestinal bacteria, and these compounds may be just as effective at selecting for certain resistant bugs as classical antibiotics. That's just one possible explanation, but it shows how complex the issue of antibiotic-resistance is, and it shows that simply saying "stop using antibiotics," without really looking at the overall problem, won't necessarily reduce MRSA.

What does the presence of MRSA in food mean? Who knows? MRSA is a pretty high profile bug, and with good reason, because it's a very important cause of infection in people. A key aspect of MRSA in food is that cooking food will kill the bacteria (as well as many of the other harmful bacteria that often contaminate raw meat). So proper attention to food safety, including thorough cooking, cleaning of surfaces, prevention of cross-contamination and hand hygiene, should greatly reduce any risk (the problem is a lot of these things aren't usually done very well).

Staph schleiferi in dogs

Staphylococcus schleiferi doesn't get much respect. Most of the attention gets paid to Staphylococcus aureus (because MRSA, the methicillin-resistant version, is such a high profile pathogen in humans and it can be transmitted between people and pets) and S. pseudintermedius (because it's a leading cause of infection and MRSP, the methicillin-resistant type, is spreading very quickly and widely in dogs).

Staphylococcus schleiferi is another Staphylococcus species that can cause various infections in dogs, particularly skin and ear infections. It's often overlooked, or more specifically, unnoticed. The problem is it takes some effort to differentiate it from other staph. This species is relatively unique in that it has two distinct subtypes - S. schleiferi coagulans and S. schleiferi schleiferi. The first one is very similar to S. pseudintermedius, and not all diagnostic labs go through the trouble of trying to distinguish one from the other. So there may actually be a lot of S. schleiferi infections that get mistakenly diagnosed as S. pseudintermedius. The second subtype is coagulase-negative (whereas S. pseudintermidius, S. aureus the first subtype of S. schleiferi are all coagulase-positive) and most diagnostic labs don't do any identification of coagulase negative staph. As a result, we only have a superficial understanding of it and its epidemiology.

A recent study from the University of Pennsylvania (Cain et al., J Am Vet Med Assoc 2011) that looked at 225 dogs with S. schleiferi infections has provided some insight into this perhaps not-so-unusual bug. Some highlights:

Ear infections and skin infections accounted for 87% of cases.

  • That's expected, since these are very common types of infections for any kind of staph.

Allergic skin disease was the most common underlying disease.

  • That's also not surprising. Most staph infections occur secondary to some underlying problem or procedure (e.g. surgery). This shows the importance of taking the time and effort to diagnoses and control allergic skin disease, in order to help prevent infections before they occur.

57% of S. schleiferi  isolates were methicillin-resistant.

  • Ugh! I'm not very surprised but it's scary how often we see methicillin-resistance in some staphylococci, because of the complications it can cause with treatment. Methicillin-resistant staph infections can be hard to treat because there may be few effective antimicrobials available.

Methicillin-resistance was more common in the coagulase negative subspecies, S. schleiferi schleiferi.

  • It's hard to say whether this means a lot from a clinical standpoint. In generally, coagulase negative staph are much less of a concern than the coagulase positive staph since they are less likely to cause disease. However, we don't really understand the differences between the two S. schleiferi's. If the coagulase-negative version is less able to cause disease, then a lower rate of methicillin resistance in the more concerning coagulase positive type is better than vice versa, but I'm not sure we have enough evidence to say much about this at the moment.

Treatment with a penicillin (e.g. amoxicillin), first generation cephalosporin (e.g. cephalexin) or 3rd generation cephalosporin within the preceding 30 days was associated with having methicillin-resistant S. schleiferi.

  • That's not surprising and is one more piece of evidence that "routine" use of antibiotics can contribute to selection for methicillin-resistant staph. It shows how we need to focus on prudent use of antibiotics.

A question I sometimes get is whether an animal with methicillin-resistant S. schleiferi poses a risk to people. We don't really know, but the risk is probably quite limited.

  • S. schleiferi coagulans infections in people are extremely rare, so this bug doesn't seem to have much of an affinity for humans.
  • S. schleiferi schleiferi infections in people are more common, but it is thought that this subtype is a "human Staphylococcus." Therefore, while it can cause infections in people (usually infections in people that are already sick and/or in hospital), it probably comes from people, not animals.
  • So, overall, the risk posed by infected animals is minimal. However, some S. schleiferi can be very drug resistant and you don't really want to have an infection with a multidrug resistant bacterium of any kind ("you're case is very unique" isn't something you want to hear from your doctor), so using good general infection control and hygiene practices around infected dogs makes sense.

MRSA control in animals..Finnish style

As MRSA in animals gets more attention, there have been increasing efforts to develop guidelines to reduce the incidence and impact of this important zoonotic pathogen. Among these are a set of recommendations developed in Finland for the prevention and control of MRSA infections in animals (or metisilliiniresistentti Staphylococcus aureus, as they would say in Finnish).  Apart from the abstract which is translated into English, the document is entirely in Finnish, but it might be of interest to any of our readers that are proficient in that language (presumably a pretty small subset).  This is clearly a worldwide issue, and it's important that it is addressed on a worldwide basis.

MRSA from foal to girl

A case report highlighted by and presented at the ASM/ESCMID MRSA conference in Washington DC last week described a horse-associated methicillin-resistant Staphylococcus aureus (MRSA) infection in Dutch girl.

The girl, a 16-year-old with a severe neuromuscular disease who was wheelchair-bound and on a ventilator, developed an infection following an insect bite. When the infection didn't respond to initial treatment, a sample was taken for culture and MRSA was identified. The girl didn't have any known risk factors for MRSA infection but had had close contact with a foal. The Friesian foal had been at a veterinary hospital prior to the girl's infection. It had a wound infection that was successfully treated with antibiotics, but no culture was taken at the time. The foal was considered a possible source of the MRSA, particularly since the strain that was recovered was ST398, which is widely found in livestock and which is regularly seen in horses in the Netherlands. After the girl's infection was identified, the foal was tested and was also found to be carrying MRSA. The girl's infection was successfully treated and the foal eliminated MRSA carriage without treatment (which is expected in horses because long-term carriage of MRSA seems to be rare to non-existent in this species).

The source of the infection could not be definitively proven, but given the fact that the horse was at a facility that regularly sees MRSA cases, that the strain involved is typically associated with livestock, and that the girl had no other livestock contact, it's a reasonable to assume it came from the foal.

We've known for a few years that MRSA is an issue in horses, and that it can be passed between horses and people - in both directions. Equine veterinarians and horse owners have abnormally high MRSA carriage rates. MRSA carriers are people who have MRSA living in or on them (most often in the nose) without any signs of infection. Most carriers never have a problem, but disease can develop in some situations. The incidence of human MRSA infections transmitted from horses is low, although it's almost certain that many horse-associated MRSA infections are not reported because the link with horses isn't made or people don't mention the horse contact. article is incorrect in stating that this is only the third case of horse-to-human MRSA infection, since we've already published two such reports, one of which included multiple cases. Regardless, it's an uncommon problem but it is probably also under-recognized. Horse owners shouldn't panic about MRSA, but they should realize that MRSA is circulating in the horse population and that by nature of their frequent and close contact with horses, they are at higher risk for MRSA carriage, and likely also infection.

More information about MRSA in horses can be found on the Worms & Germs Resources - Horses page.

(click image for source)

New BSAVA guidelines for MRSA/MRSP

The British Small Animal Veterinary Association (BSAVA) has updated its practice guidelines for management of MRSA and MRSP.

Overall, there’s good information in the document with an emphasis on routine infection control as the key measure to reduce the impact of MRSP and MRSA. I’d like to see more emphasis on developing an overall infection control program, but the emphasis on basic principles such as hygiene is good.

Like any guideline document, there will be some disagreements in recommendations. I agree with the majority of what's written, although there are some recommendations that I wouldn’t make, and some additional areas that I’d address. That’s not surprising since most of the recommendations are based on opinion rather than evidence because we don’t have solid evidence for most areas, and there isn’t necessarily a single "right" answer to many questions at this point.

Typically, guidelines assess and report the level of evidence on which recommendations are based, but that’s not done here. Letting people know the evidence (or here, the relative lack of evidence) is a useful part of guidelines. How the recommendations are worded can also play a role. Here, they perhaps overstate the strength of evidence through use of wording such as saying something "will" have an impact, when we really should say it "might." In the absence of evidence, good common sense measures can be recommended and implemented, however we need to remember that we have major limitations in our knowledge. We need to figure out which infection control practices are effective.

I have a major problem with one recommendation: "Colonised animals should be treated with a chlorhexidine shampoo and intranasal fusidic acid or mupirocin once daily." There is simple no evidence supporting the use of active measures to eliminate MRSA and MRSP.

  • For MRSA, there is reasonably good evidence that dogs and cats eliminate it on their own in a reasonably short period of time.
  • For MRSP, we simply don’t know how long they can be carriers. I suspect that long-term carriage can happen in some animals, so decolonization might be attractive, but we don’t know what to do yet.
  • There is absolutely no evidence that intranasal antibiotics are effective in dogs and cats. I have serious doubts that someone can adequately administer a topical antibiotic to the nasal passages of a dog, and particularly a cat.
  • If this recommendation is adopted and widely used in the UK, I suspect the country will be an international leader in fusidic acid- and mupirocin-resistant bacteria.

Overall, there are some good recommendations in the guidelines, including the general infection control sections. We need to improve our baseline level of infection control and hygiene to reduce the impact of MRSA, MRSP and a variety of other concerning microorganisms. At the same time, we need to acknowledge our limited knowledge in a lot of areas and the fact that we are really working based on common sense and extrapolation from human medicine, with little direct evidence from veterinary medicine. Much more research is necessary, a major limitation of which is the limited priority given to companion animal infection control by research funding agencies.  This has to change to help control the impact of bugs like MRSA and MRSP on both animals and people.


MRSA, spider bites and denial

Bites from the brown recluse spider (see photo left) can be pretty nasty, and produce tissue damage similar to a typical MRSA skin and soft tissue infection. Despite the epidemic of MRSA that's ongoing in many regions, particularly the US, MRSA infections are still sometimes misdiagnosed as spider bites.

To a degree, I can see why this might happen in areas where the brown recluse spider lives (i.e. the yellow area on the map at right) and where these spider bites certainly occur.  Even in these regions though, taking a culture to rule out MRSA is about as simple as it gets. Sadly, erroneous spider bite diagnoses also happen in areas where the brown recluse spider doesn't even exist.

A colleague from the University of Iowa, Dr. Tara Smith, recently described a nice example of this on her blog Aetiology:

Does this relate to animals? Not really. Unlike people, animals rarely develop the type of skin infection that mimics a spider bite, so misdiagnosis as a spider bite is unlikely (although it does sometime occur). Failure to properly consider MRSA and test for it is still a problem in animals.

Source of images:


Staph food poisoning...possible pet reservoir

When it comes to public health concerns about staphylococcal bacteria from pets, most of the attention gets paid to methicillin-resistant strains like MRSA. That's not surprising considering how important MRSA is in human medicine. However, staph that aren't methicillin-resistant can also be a problem, since they can cause the same types of infections that resistant types can (they are just easier to treat). Another issue that often gets overlooked is staphylococcal food poisoning.

Staphylococcal food poisoning is one of the most common foodborne illnesses and results from growth of certain strains of staphylococci in poorly handled or stored foods. If staph get into food and the food is kept at improper temperatures, the bacteria can grow. If the strain of staph that's in the food is one that can produce enterotoxins, these toxins can accumulate in the food at high enough levels to cause food poisoning when eaten. In most cases, people are probably the origin of enterotoxin-producing staph that contaminate food, but pets are another possible source.

A recent study in Vector-borne and Zoonotic Diseases (Abdel-moein et al 2011) looked at enterotoxigenic staph in 70 dogs and 47 cats. Swabs were collected from the mouth, nose and wounds. Nasal swabs were also collected from 26 people. The researchers isolated enterotoxigenic Staphylococcus aureus (strains of S. aureus that possessed genes for enterotoxin production) from 10% of dogs and 2.1% of cats, as well as 7.7% of people. Most of the positive samples from pets were oral samples.

This study shows that dogs and cats can be potential sources of strains of S. aureus that cause food poisoning. Since the staph are often in the animals' mouths (and therefore presumably shed in saliva), animals can potentially contaminate food with these enterotoxigenic staph fairly easily, but it's unknown how often this occurs.

Prevention measures are pretty basic but should be considered, including:

MRSA transmission between hamster and human

The more we look, the more we find when it comes to MRSA (methicillin-resistant Staphylococcus aureus). As people start looking for it in different animal species, it's often found. We've found it in many species already, including dogs, cats, rabbits, pigs, walruses, dolphins and alpacas, so it's not a big surprise to see a recent paper in the Journal of Clinical Microbiology (Ferreira et al 2011) about suspected MRSA transmission between a human and a hamster.

The case report describes a person with advanced cystic fibrosis who had undergone a lung transplant and had various other medical problems. Prior to another surgical procedure, MRSA was identified through routine pre-operative screening. Nasal and rectal swabs were then collected from the person's three pet hamsters, one of which was positive. The MRSA isolates from the human and hamster were the same, supporting transmission from one to the other. Given the person's underlying health problems, frequent contact with the healthcare system, the typical human origin of the strain that was found, and limited contact of hamsters with other animals or people, it is most likely that MRSA was transmitted from human to hamster in this case.

The paper concludes with: "Should testing of the pets of MRSA-positive patients be recommended? At this point, we recommend that MRSA-positive patients be informed that their companion animals can be potential sources of infection or reinfection. In the presence of a MRSA-positive human or animal, heightened hygiene practices should be instituted and unnecessary close contact should be avoided. Screening of household pets might be indicated in situations of recurrent MRSA infections despite adequate treatment or when immunocompromised patients live in the household."

That's consistent with our standard recommendations and hits most of the key points:

  • Awareness is critical. People need to know what the risks might be and what they can do about them so that they can make informed decisions and realize why recommendations are being made.
  • Testing of pets is rarely useful, particularly in the absence of a recurrent MRSA problem.
  • Good hygiene practices are critical.

I don't really agree with the comment that testing of pets might be indicated when immunocompromised people are in the household (although the comment is properly hedged by saying "might be indicated"). A large percentage of the population has some degree of immunocompromise, and there's a huge spectrum from minimal risk to tremendous risk. Even in high-risk patients, screening is questionably useful to me because it doesn't really change what I'd do.

  • If I screened a hamster from a high-risk person and found MRSA, I'd say that it probably came from the person, that it's possible it could be transmitted back to the person, that good hygiene practices should be followed and close contact should be restricted. There's no indication (or ability, in reality) to treat the hamster.
  • If the hamster was negative, I'd say it was possibly negative because screening is not 100%, that the hamster could be exposed to MRSA from the owner at any time, and so to manage unknown colonization and reduce human-hamster transmission, I'd recommend good hygiene practices and restriction of close contact.
  • If I'm going to do the same thing with a positive and negative result, I don't do a test.

This paper should be yet another reminder that we live in a complex relationship with our pets, including microbiologically. While we need to consider the role of pets in human infection (and the role of humans in pet infection), and we need to balance that with the positive aspects of pet ownership in order to maximize the benefits while minimizing the costs.

Aromatherapy, topical treatment and toxicity

I have no problem with people considering "alternative" therapies for the treatment of infections. I perform research on non-antibiotic alternatives and hope that results pan out in the field. I have problems, however, with people that use unproven alternative therapies in lieu of proven conventional treatment or stray from the "do no harm" philosophy.

I read an article on aromatherapy in pets that highlighted my concern. Someone can make Fluffy or Fido smell whatever they want (although my dog Meg's concept of what smells nice certainly differs from mine - she'd rather roll around on a decomposing carcass than a lavender plant). I don't think it's going to help, but it shouldn't hurt. This article went beyond that, though, talking about application of substances to treat infections. Putting tea tree oil into a dog's ear isn't aromatherapy, it's topical therapy.

Is it an issue of semantics? No.

Essential oils like tea tree oil have some powerful properties. Just because it's "natural" doesn't mean it's safe. We know that tea tree oil has antibacterial properties. However, we also know it can be toxic. There are reports of serious adverse effects in people from tea tree oil ingestion and I know of severe reactions in dogs (including 1 death) thought to be due to excessive tea tree oil application. Adverse effects can result from the dog ingesting the oil by licking it off its coat or from direct effects on the skin.

A research study presented by Dr. Becky Valentine at the 2011 North American Veterinary Dermatology Forum highlighted this concern. Her research showed that while tea tree oil was able to kill methicillin-resistant Staphylococcus pseudintermedius (MRSP), a leading cause of canine ear and skin infections, it was also quite toxic to canine skin cells. So, the cost-benefit of tea tree oil is unclear since it certainly has some toxic properties, particularly when compared to other topical therapies such as chlorhexidine, that are essentially non-toxic.

Additionally, in a good demonstration of "all pain, no gain," Dr. Valentine's research showed that grapefruit seed extract, another compound available over the counter, had no effect on MRSP but had significant toxic effects on canine skin cells.

What does this mean? It means that essential oils and any other alternative therapies need to be studied, just like any other treatment. We need safety studies to know they won't cause problems, dosage studies to know how to use them and efficacy studies to know if they work. Natural products can be quite powerful and potentially useful, but they need proper testing.

MRSP transmission between people and pets

Today (like most days) I answered questions about the potential for transmission of methicillin-resistant Staphylococcus pseudintermedius (MRSP) between people and pets. We have a long way to go before we fully understand the issues, but research continues to progress and we're learning more and more. A recent study by Dr. Engeline van Duijkeren and colleagues from Utrecht University published in Veterinary Microbiology (van Duijkeren et al. 2011) steps up our knowledge another notch.

In their study, the authors enrolled 20 households that owned pets with MRSP infections. They went into the households and collected samples from the index pet (the one with the MRSP infection), other pets, people and the household environment.  At the time of sampling, 10 of the infected pets had gotten over their illness while the other 10 still had active infections.

Some highlights of the study:

  • 4/14 (36%) of other dogs and 4/13 (31%) other cats in the households were MRSP carriers. In households where the pet still had an active infection, an astounding 86% of the other animals were carriers. All these numbers are much higher than the expected baseline rate of MRSP carriage by healthy pets in households, giving strong support to the notion that MRSP is being passed between pets in households with an infected pet.  From an infection control standpoint, it's probably reasonable to assume that a pet living with an infected animal is a carrier.
  • MRSP was isolated from 2/45 (4%) of nasal swabs from people. This is not too surprising, since we know that MRSP (and its susceptible counterpart, methicillin-susceptible S. pseudintermedius (MSSP)) can be transmitted between people and pets. This study shows us, however, that even when there is apparent MRSP transmission going on between pets in the household, it doesn't seem to commonly involve people.
  • MRSP was found in the environment in 70% of houses (and 90% of household where the pet was still infected). These are pretty big numbers but are not really unexpected, since if MRSP is in and/or on animals, it's bound to be found in the environment. Whether the environment is a potential source of human or animal infection isn't known, but it's something to consider.

This research gives more evidence that MRSP can be spread readily between animals but less so between animals and people. It could be because animals have closer contact with each other in a household than with people, but a bigger factor is probably that S. pseudintermedius is more adapted to living on animals than on people.

MRSP info sheet update

The ever-popular methicilin-resistant Staphylococcus pseudintermedius (MRSP) owner information sheet has been updated and can be found, along with info sheets on many other topics, on the Worms & Germs Resources page.

More on vets and MRSA

There are a number of published studies regarding methicillin-resistant Staphylococcus aureus (MRSA) carriage by veterinarians, most reporting high rates compared to the general population. This is a concern because MRSA is an important cause of disease in both people and animals. Just having MRSA living in your nose doesn't mean you're going to get sick. Indeed, around 2-3% of normal, healthy people are likely carrying MRSA at this moment. However, if you are carrying MRSA, you are at increased risk of developing an infection under certain circumstances. In veterinarians MRSA carriage is also a concern because of the potential for transmission to patients (and potentially from those patients back to people).

A recent Australian study in the Australian Veterinary Journal (Jordan et al 2011) looked at MRSA carriage in different types of veterinarians. The rates were:

  • 0.9% in industry and government veterinarians (who have limited contact with animals)
  • 4.9% in small animals veterinarians
  • 11.8% in veterinarians with horses as a major component of their caseload
  • 21.5% in equine veterinarians

These results are similar to some of our earlier studies, with carriage rates in small animal veterinarians being  higher than would be expected for the general population, and carriage rates in equine veterinarians being very high.

Why do veterinarians have high rates of MRSA carriage?

There's no definitive answer but there are some likely causes. Veterinarians have contact with large numbers of pets and horses, and we know these animals can carry MRSA. Even if the percentage of dogs, cats or horses carrying MRSA is very low, when you multiply that by the number of animals a veterinarian touches every week, you can see how contact with an MRSA-carrier is pretty likely. Veterinarians also tend to have close contact with sites where MRSA can be found, such as the nose. This makes the chance of having contact with the bacterium itself more likely. An additional issue the often sub-optimal use of routine infection control and hygiene practices (especially hand hygiene), which may also increase the risk of MRSA transmission. Put all these together, and it makes sense that veterinary personnel are at increased risk.

Why do carriage rates tend to be higher in equine veterinarians?

It could be because MRSA is more common in horses than small companion animals. Another plausible explanation is the fact that the horse's nose (the most likely site for MRSA to be living) is commonly touched during examination and restraint, and horses have pretty big noses to start. Additionally, good hygiene can take more effort on some farms, as sinks and often even hand sanitizer are not as readily available as they are in a clinic.

More information about MRSA in companion animals can be found on the Worms & Germs Resources page.  More information about MRSA in horses can be found on our sister site, on the equIDblog Resources page.

(click image for source)

This Worms & Germs blog entry was originally posted on equIDblog on 19-Apr-11.

Vets sued over MRSA

When I give presentations to veterinarians about infection control, I often talk about legal liability as one reason they need a good infection control program. I talk about the potential bad scenarios, such as someone getting an MRSA infection from an animal and then turning around and suing the vet. I usually say something like "I don't think it's happened yet, but you never want to be an index case". I may need to change that line now that a Texas veterinary clinic is being sued over a person's MRSA infection.

However, the lawsuit, filed April 4, isn't from an owner. Rather, it's from a veterinary assistant. The woman is suing the clinic, claiming they were negligent because they didn't warn her that she would be caring for an MRSA-infected animal. She claims that she contracted the infection on the job and that it "has physically impaired her for the rest of her life."

I know nothing about this case beyond what's in the link above, however it raises a few important issues and questions.

What does this mean for the veterinary clinic?

  • I've been saying for years that the bar is being raised and clinics need a good infection control program, including training and education, to reduce infections of both pets and people.
  • As awareness of zoonotic diseases and veterinary infection control increases, the potential for lawsuits may similarly increase.

What level of warning is required for veterinary employees?

  • This varies with the type of person.
  • A veterinarian shouldn't need to be informed that they will work with animals carrying zoonotic pathogens. If they didn't pick that up in vet school, they've got some other major issues.
  • A veterinary technician should have a similar understanding of the risks and measures that should be undertaken to reduce those risks.
  • Lay personnel are a different story. You can't assume a lay employee has any knowledge whatsoever about infectious diseases, zoonotic diseases or infection control.
  • If there are minors in the clinic (e.g. co-op students, volunteers), you need to go even farther, and there should be written notification of parents of the risks, and measures that are taken to reduce the risks.
  • In general, the less the veterinary education, the greater the need for clear and documented education about disease avoidance.

How do you prove this person acquired MRSA on the job?

  • That's tough. Perhaps there was a clear link with a case. Even stronger would be showing that the human and animal MRSA strains were the same, but that's unlikely to have been done. Just because MRSA can be found in animals doesn't mean that MRSA infections all come from animals. Humans are thought to be the source of the vast majority of MRSA infections and pets, and while pets can potentially spread it back to people, this is ultimately a human disease. People pick up MRSA all the time in the general population, although the percentage  of people who carry it at any given time is still low.
  • MRSA carriage rates have been shown to be higher in veterinarians than in the general public in a few different studies. I think it's clear that MRSA exposure is a risk of veterinary practice. However, proving that an individual infection came from a pet in a clinic is still difficult.

How can vet clinics reduce the risk of MRSA (and other) infections, as well as lawsuits?

  • Have an infection control program in place.
  • Make sure infection control practices and policies are written down.
  • Make sure all employees are appropriately trained and document the training.
  • Make sure people follow all of the required protocols.

Infection control isn't rocket science. At its heart, it's the application of some very basic practices. Infection control hasn't had a high profile in companion animal veterinary medicine in the past, but things are changing (albeit slowly). Available resources can help veterinary clinics implement a decent infection control program with minimal effort. A good resource is the document Infection Prevention and Control Best Practices for Small Animal Veterinary Clinics, which is available (free) for download on the Worms & Germs Resources page.

Treat the pet, not the lab result

The title of this post describes a very basic concept, but one that is sometimes forgotten or hard to follow. The key point is that the goal of treating a sick pet is to make the pet well. Getting well and getting "normal" laboratory data aren't necessarily the same thing.

A question that comes up a lot with MRSA, MRSP and other bacterial infections is "should my pet be tested after treatment to see if the bug is gone?" The answer is usually "no."

One reason to not re-test is just what I said above. The goal of treatment is to make the patient healthy. That doesn't necessarily mean that MRSA, MRSP or whatever bug is causing the problem needs to disappear. In fact, the bacterium that causes a given infection often remains (in smaller numbers) in or on the body somewhere. If it's a skin infection, the bacterium may still be present on the skin where the infection was. However, if the body is handling it well, then it's not necessarily a problem. We have to remember that every animal (and person) has multiple types of bacteria in or on it that can cause disease given the right circumstances. We're never going to eliminate them all. In fact, trying to get rid of all potentially bad bacteria would probably result in bigger problems.

Another concept that I emphasize a lot is only do a test if you have a plan for using the result. If you don't have a clear reason to do the test, and if the result won't impact your decisions or provide information you need in the future, then why do it? While a negative culture might be nice to see, it's not necessarily a guarantee that a particular bug is gone. Furthermore, a positive culture doesn't lead to actions that are any different from those that would be taken if the culture is negative in most situations because, as mentioned above, we're looking for clinical cure (getting better) rather than microbiological cure (getting rid of the bug). Rarely would we extend treatment or do anything different in response to a positive culture in a healthy animal.

The bottom line is post-treatment cultures are rarely needed. There may be some circumstances where testing after treatment is useful and where the results would lead to a defined plan of action, but these are few and far between.

Image: A Mueller-Hinton agar culture plate being used to test the antibiotic susceptibility of a bacterial isolate according to the Kirby-Bauer method. (source: CDC Public Health Image Library #10785)

I have MRSA...should my pet be tested?

I get this question a lot, from both pet owners and veterinarians. Typically, my answer is "no."

Why not?

  • The two big questions I always ask are "why do you want to know and what would you do with the results?"

Sometimes people want to know their pet's MRSA status to see if the pet was the source of their infection.

  • However, MRSA in pets is typically associated with MRSA in humans, i.e. if a pet is carrying MRSA, it probably got it from the owner or another close contact. Finding MRSA in a pet after someone is diagnosed with an MRSA infection doesn't mean the pet was the source. More likely, the person got MRSA somewhere else and passed it on to their pet.

Sometimes, people want to know if their pet is at risk of an infection.

  • Carrying MRSA presumably increases the risk of an MRSA infection, but likely only in animals already at risk of an infection because of underlying disease or other risk factors such as surgery. The risk to the average pet from short-term MRSA colonization is probably limited. Also, if the pet was identified as a carrier, we wouldn't be doing anything to eliminate carriage, since we have no idea if decolonization therapy is effective in animals, and it doesn't seem to be needed (because dogs and cats almost always get rid of it on their own). Therefore, it's hard to justify screening for this reason. If the animal was getting ready to undergo surgery, then that might change my answer.

For me, it's also very important to consider what you'd do with the results of any test. In general, in a household where a person has an MRSA infection:

If the pet tests negative, I'd say that it doesn't 100% guarantee that the pet is truly negative, since no screening test is absolutely 100% sensitive. Also, the test only tells you the status of the pet at the time of sampling. It could have picked up MRSA five minutes after the swabs were taken. So, a negative result means the animal is probably negative. Since it's not absolutely negative and since the pet would be at risk of picking up MRSA from the infected person after it was tested, I'd recommend close attention to hygiene around the pet (especially good hand hygiene and avoiding contact with the nose) to reduce the chance of the pet becoming colonized and to reduce the risk of MRSA transmission from pet to person if the pet was actually a carrier.

If the pet tests positive, I'd say that we certainly couldn't say the pet was the source of infection. More likely, it got it from the person with the infection. Since we know that MRSA carriage in dogs and cats is almost always transient, and that they will almost always get rid of it on their own if re-exposure is prevented, I'd recommend close attention to hygiene around the pet (especially good hand hygiene and avoiding contact with the nose).

Since my response to either result would essentially be the same, why test?

Efforts are better spent on good household hygiene practices and restricting contact with high risk sites. On both pets and people, this would include the nose, as well as any sites that are infected or sites that are prone to infection (e.g. skin lesions). That's going to be much more worthwhile and rewarding than testing the pet.

MRSP in the park

As multidrug-resistant bacteria such as methicillin-resistant Staphylococcus pseudintermedius (MRSP) become more common in pets, there are increasing questions about how to manage animals that carry them. A particular issue is what to do with carriers - animals that don't have any sign of disease but still carry the bacterium.

A small but increasing percentage of healthy dogs and cats are currently carrying MRSP in their nose or intestinal tract. The rates appear to be shooting up in most areas, and I suspect that the current carriage rate in a lot of regions is above 5%. In some groups of animals, particularly those that have received repeated courses of antibiotics, rates are likely much higher.

Back to the initial question... what to do with MRSP carriers?

Well, in some ways, we want to limit their contact with other animals to reduce the spread of the bacterium. However, we also have to realize that this is now a rather common bacterium, and it doesn't cause infections in the majority of animals that get exposed, and it is very rarely a problem in people. That doesn't mean we should ignore it, but it's a lot easier to justify being very strict with a bug that:

  • is readily transmitted to people and can cause disease in people.
  • is rare in the dog population.
  • is highly infectious.
  • usually causes disease when an animal is exposed.

These aren't the case with MRSP. It's still certainly a serious concern, but where do we draw the line between being proactive and being impractical?

Back to the title of the post... what to do with MRSP-positive dogs that go to dog parks?

It's a good question, and I don't have an answer in which I'm 100% confident. The paranoid infectious diseases part of my brain wants to keep MRSP carriers away from other dogs to reduce transmission. But, the practical part of me recognizes that parks are probably a limited source of transmission overall, that there are probably greater risk factors for the increase in MRSP, that we have no idea whether short-term contact such as meeting in passing at a dog park can result in efficient transmission, and that going to the park is an important activity for many people and their dogs.

Anyone that takes their dog to a dog park needs to understand they are increasing the risk of infectious disease transmission to (and from) their dog. This includes a wide range of bacterial, viral, parasitic and fungal diseases, not just MRSP. In fact, I think there are other pathogens that are a bigger concern from dog park exposure.

Should MRSP dogs be keep away from dog parks?

  • When they have an active infection and are presumably shedding larger numbers of bacteria: Yes.
  • When they are just carriers: Probably not.

How can I say that when I keeping talk about how big a deal MRSP is?

  • It's a big deal, but it's mainly a big deal in specific circumstances, such as in dogs undergoing surgery, dogs with underlying skin disease and dogs that are exposed to antibiotics. There is no such thing as a no-risk dog, but the individual risk for a healthy dog is probably very low.
  • You have to live. You can do the Howard Hughes model of infection control and barricade yourself in your room, or you can live life. Yes, that increases risk. But, we do things to contain that risk as much as possible, such as keeping sick dogs away from parks (to prevent both transmitting and picking up microorganisms), reducing antibiotic use and using good general hygiene practices.
  • You don't want to purposefully infect other dogs, but the small number of known MRSP carriers is dwarfed by the thousands of dogs that are unknown carriers.
  • In some respects, MRSA is the human version of MRSP, and it's a huge health problem. However, MRSA carriers are not locked away. We realize they are transmission sources but we focus efforts on carriers only in high risk situations, such as hospitals. Could we greatly decrease MRSA carriage in people by aggressively testing, treating and quarantining? Sure. Is it worth it? That's pretty questionable.

I never want to give the impression that we are being lax with an important infectious disease, but I just don't have the evidence (or anecdotes) that restricting park access for carriers will do anything for MRSP control, especially since known MRSP carriers probably represent 0.0001% of all MRSP carriers.

What can you do to reduce the risk of transmitting or acquiring MRSP at the park?

  • Pick up feces. Dogs can shed MRSP in feces, and this could be the most important route of transmission given how some dogs like to nose and eat feces (my dog being the poster child for that particular habit).
  • Watch your dog closely so it doesn't eat feces (or at least is less likely to).
  • Don't let your dog have contact with an animal with any signs of an infection, particularly a skin infection.
  • Try to limit nose-nose, nose-bum contact (of the dogs... I assume you're limiting that type of contact between yourself and other dog walkers).
  • If you have a dog that is high-risk for getting an infection, consider keeping it away from the park, reducing the amount of time it spends in the park or limiting off-leash time. This includes dogs with wounds, dogs that have recently had or are going to have surgery, dogs with active skin disease, dogs on immunosuppressive therapy (such as steroids), and dogs on antibiotics, among others.

More information about MRSP can be found on the Worms & Germs Resources page.

(click image for source)

Is Staphylococcus schleiferi zoonotic?

Methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. pseudintermedius (MRSP) get a lot of media attention because of the ever increasing numbers of infections in dogs and cats, and concerns about transmission to people. However, there are many other methicllin-resistant staph of varying relevances. One is an interesting related bug called Staphylococcus schleiferi.

There are actually two types of S. schleiferi:

  • S. schleiferi schleiferi: This is a coagulase-negative subspecies that occasionally causes skin and ear infections in dogs (and uncommonly cats). It can also be found in healthy animals. There are a few reports of infections in people, mainly surgical site and wound infections in individuals who are at high risk of infection because of hospitalization, surgery or other factors.
  • S. schleiferi coagulans: This is a coagulase-positive subspecies that may be more common in dogs and cats than S. schleiferi schleiferi, causing skin and ear infections and also being found in healthy animals. Human infections are very rare.

Currently, there is little to no evidence the animals are a source of human infection with S. schleferi and human infections appear to be very uncommon. However, this is an area that hasn't been studied much so it's hard to say with any confidence that there is no risk. My assumption is that the risk is very low, but not zero, so while we shouldn't be paranoid, it makes sense to use some very basic infection control practices when dealing with infected animals to reduce any possible risk. These would include:

  • avoiding contact with infected sites
  • if contact with infected sites is necessary (e.g. cleaning or treating infected ears), gloves should be worn and hands washed after glove removal
  • hands should be washed thoroughly after any contact with the infected site, and regularly after contact with the animal

Quarantine of infected animals in households isn't necessary, because of the limited evidence of transmission and because healthy dogs and cats can also carry this bacterium. In veterinary clinics, isolation of infected animals is reasonable because other animals in the clinic may be at higher risk of developing infections should they become exposed.

Internet advice: The good, the bad and the ugly

The internet can be a strange place at times. You can find great, reputable and unbiased information right next to complete garbage. Often, the garbage is pretty apparent, but sometimes it's dressed up well or mixed in with some good information. That's a problem with veterinary advice and information sites.

Among the creative myths identified in a couple of minutes of searching:

- Metronidazole is a proven treatment for parvovirus: No. Metronidazole is an antibiotic that doesn't have any effect on viruses. Antibiotics are sometimes used in the treatment of parvovirus, but they are drugs that are used to prevent or treat problems caused by bacteria from the gut entering the bloodstream as a result of the intestinal tract disease. Metronidazole won't do that.

- MRSA is a virus: You can't make much more of a basic mistake than confusing a virus and a bacterium. Anyone who says this when purportedly writing medical advice is completely clueless.

- If your dog gets an MRSA infection, your veterinarian will likely prescribe vancomycin: Only in extreme circumstances (if ever) should this ever happen. For more information on vancomycin and its use in treating animal and human infections, see our archives. (This gem is on a page that says it's information from infectious disease specialists).

-MRSA in dogs can easily become resistant to vancomycin so linezolid may be required: Fortunately, vancomycin resistance is extremely rare, having been found only a few times in people, in specific circumstances. It's never been found in a dog. Hopefully it will stay that way. (This site didn't even spell vancomycin correctly.)

- Cats can easily get a urinary tract infection if their litterboxes are not cleaned: No. There is no evidence of this and no reason to think it's an issue. Poor litterbox maintenance can lead to urinating outside of the litterbox or other problems like idiopathic cystitis, but not infection.

- In order to have a very healthy dog, it is often required to supplement your pet's diet to provide a high amount of probiotics: Nope. Certain probiotics might be useful in certain animals in certain situations, but we have no proof of this in dogs and cats, and they are certainly not needed for all animals.

There's no way to guarantee that a website is reputable or that the writers are knowledgeable, but here are some things I consider when scrutinizing information on the internet:

  • Who set up the website? Is it clear who's in charge?
  • Who wrote the information? Is it someone with actual credentials? For veterinary medical advice, is it a veterinarian? If it's a veterinarian, is it a specialist? If it's not a veterinarian, what expertise does the person have? Some people without veterinary degrees have expertise in some fields, but try to determine whether they truly have the qualifications to give advice on a particular topic. That's harder to do these days given the proliferation of mail-order "PhD" degrees, something that's not uncommonly encountered in unqualified people making poor veterinary recommendations. 
  • Why is the website there? Is it an educational site or is it there to make money? Commercial sites aren't necessarily bad but you have to consider any conflicts of interest or ulterior motives. If there is an article about something, and the last sentence tries to sell you a product to fix that problem, be careful.
  • Does the information make sense and is it consistent with other websites? You can probably find a site somewhere to support any notion that you have, but does it really make sense?
  • Is the site relevant to your geographical area? This is particularly important for infectious diseases since they can vary greatly between regions. A disease may be a big problem in one area, and a website might provide excellent advice... but only for that area. It may be completely irrelevant or inappropriate for other regions.
  • Can they spell? The odd typo probably isn't a major issue (I do it myself). However, rampant and blatant abuse of the English language and an inability to spell important words properly should be red flag.

Searching the internet for pet health information is certainly not a bad thing to do. But, you have to critically assess what you read and remember that it's not always right. Use the internet as a resource but make sure that it's to supplement advice from your veterinarian, not to replace it.

Biohazardous cell phones

It's amazing how attached people are to their cell phones. Many people will answer them without any thought of what else is going on. It's something I've seen in veterinary hospitals where wireless or cell phones are the primary mode of internal communication. The natural tendency to answer the phone often overrides the thought process of "are my hands covered in pus, blood or some other gross material that I should perhaps remove before touching this piece of plastic that will spend a lot of time against my face and which may go home with me?" We've grown some interesting things from cell phones and pagers, as have others.

A recent paper in the American Journal of Infection Control (Sadat-Ali et al 2010) provides yet another example of this. In this study, the authors cultured cell phones of 288 health care providers over a six-month period.

  • 44% of phones were contaminated with "potentially harmful" bacteria. There's no description of what they considered "potentially harmful" and I'm surprised that the percentage wasn't even higher.
  • MRSA was isolated from 7.3% of phones, from people in wards, the emergency room and the operating room.
  • 31% of people said they occasionally wiped down their phones with alcohol swabs. People who said they did this were significantly less likely to have contaminated phones.

Is this really surprising? No, not at all. We don't live in a sterile environment, and the more contact with healthcare environments, the greater the chance of contamination with healthcare-associated microorganisms. We also know that hygiene practices associated with cell phones are certainly not very common, nor have optimal ways to reduce or remove contamination been investigated.

Is this a problem? It's hard to say. Just because cell phones can become contaminated, that doesn't mean they are sources of infection. They are one of many, many potentially contaminated environmental surfaces. However, given the close contact with them and the potential that someone would touch a cell phone and then a patient, it's something that shouldn't be ignored.

Are health care workers' phones worse than other people's phones? It's hard to say. This study didn't look at a control group of non-healthcare workers. I suspect that phones owned by the general public are often contaminated as well, though perhaps not with the same range of microorganisms.

How can we reduce the risk of contamination? It's simple: wash your hands regularly. If healthcare workers washed their hands when they are supposed to (especially before and after patient contacts), the risk of contamination and the implications of cell phone contamination would be greatly reduced.

Like a lot of things in infection control, reducing the risks of this potential problem is pretty easy in  theory, but harder in practice, because the draw of that ringing phone is pretty powerful psychologically.

Image from

MRSP infection in a person

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) is becoming a huge problem in dogs (and to a lesser degree cats). I think it can easily be called an epidemic, and probably even a pandemic, considering the degree of spread, the massive increase in cases and the international distribution of this multidrug-resistant bacterium.

Public health concerns regarding MRSP have received attention because of the huge problem with MRSA (methicillin-resistant Staphylococcus aureus) in people. My line with S. pseudintermedius in general is that while there are only periodic reports of infections in people, exposure to this bacterium is very common, since it is carried by a large percentage of healthy dogs. Given the frequent exposure and very small number of infections, it’s not a particularly pathogenic bacterium for people. The same should apply for MRSP, since methicillin resistance doesn’t’ make it inherently any more able to cause disease, it just makes it harder to treat. However, I always add the statement that, while the risk is pretty low, I’d rather not have an infection with a highly drug resistant bacterium, so we need to pay attention and try to reduce the risk of transmission.

A paper in an upcoming edition of the Journal of Antimicrobial Chemotherapy (Stegmann et al 2010) shows that these concerns are not unfounded. This report, from Switzerland, described an MRSP infection in a person that developed after sinus surgery. The bacterial strain that was involved was sequence type 71 (ST71), the predominant strain found in dogs in Europe. The affected person had a dog with various health problems, but unfortunately the dog was euthanized (presumably not because of the person’s infection) before samples could be taken to see if it carried the same strain. Since we know that S. pseudintermedius can move between pets and their owners (although usually without causing any problems), it's reasonable to assume that the dog was the source of infection here.

More information about MRSP and MRSA can be found on the Worms & Germs Resources page.

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Livestock-associated MRSA in dogs

A study we just published in the journal Veterinary Record (Floras et al 2010) described an MRSA outbreak in a dog breeding kennel. That's a little unusual in itself, but considering how MRSA is spreading amongst the dog population, it's not really astounding. What was unique about this outbreak was the strain of MRSA that was involved, sequence type 398 (ST398).

ST398 MRSA is commonly referred to as livestock-associated MRSA, since this strain seems to have originated in pigs, and is commonly found in pigs and calves in some regions of the world. It can also infect people, and high rates of carriage of this MRSA strain can be found in pig farmers, pig vets and other people with close contact with livestock. In some areas of Europe, this strain is a big problem, accounting for a large percentage of human MRSA infections. Interestingly, it seems to be a rare cause of illness in people in North America (at least at the moment).

Dogs seem to be innocent bystanders when it comes to MRSA. The vast majority of MRSA strains found in dogs are common human strains, indicating that, ultimately, MRSA in dogs originated in people. There are only two other reports of dogs with ST398, both from Europe. One was a dog with a skin infection. The other was a healthy dog (a carrier) who was owned by a pig vet. 

This kennel outbreak involved a larger number of dogs, including both healthy carriers and sick dogs. Overall, MRSA was isolated on at least one occasion from 23/42 (55%) dogs in the kennel. In a couple of litters, most of the puppies were identified as carriers, but fortunately most stayed healthy. MRSA caused skin infection in one puppy and mastitis in a mother dog, and was also found in the respiratory tract of a puppy that died (although it may or may not have been the cause of death).

The source of the ST398 was not identified. One of the owners worked on a pig farm, but MRSA was not isolated from either owner. It's most likely that the owner did bring MRSA home from the farm, either as a transient carrier (in their nose) or as a contaminant on their skin. Regardless, once it got into the kennel, it was able to move between dogs, either from dog-dog contact or with the help of human hands. Fortunately, ST398 MRSA carriage by dogs seemed to be transient in this situation, which is consistent with what we know about carriage of other strains. MRSA is not really adapted for long-term survival in dogs, so they only carry it for short periods of time. That's a big advantage when it comes to trying to control this pathogen.

While we have to be careful to not over-interpret data from only a few studies, this report indicates that ST398 can cause disease in dogs and it can be present in apparently healthy dogs. It can also be spread relatively easily amongst dogs in a breeding kennel situation. While a pig-link was not confirmed, it's reasonable to suspect that dogs with contact with pigs (and perhaps other livestock) might be at higher risk of developing ST398 infections, as is the case with people.

This is a perfect example of the one medicine concept, and why we need to think about infectious diseases in broad terms, not just focusing on specific populations or species. This situation involved a pig Staphylococcus aureus that somehow acquired methicillin-resistance, spread widely around the world (most likely in pigs, initially), spread to people, and then likely spread to another species, in this case dogs.

(click image for source)

Sequence type 398 MRSA infection from horse to human

Methicillin-resistant Staphylococcus aureus (MRSA) is a huge problem in people and is an emerging pathogen in horses. Most earlier reports of MRSA in horses involved one strain, called CMRSA-5 in Canada, USA500 in the US, and sequence type 8 (ST8) as a more general term. This human-origin strain seems to be adapted for survival in horses, and in North America, this strain has accounted for most MRSA infections in horses and MRSA infections in people linked to horse contact.

Another MRSA strain, ST398, has recently emerged as a big problem associated with livestock (particularly pigs). This strain is very common in pigs internationally, and is a major cause of infections in people in some European countries. There are also a few reports of ST398 in horses. Most are from Europe, although we have found this strain in one horse in North America. At last week's ASM Conference on Antimicrobial Resistance in Zoonotic and Foodborne Pathogens in Toronto, Dr. Engeline van Duijkeren from the Netherlands presented a case of human ST398 infection linked to a horse.

In the reported case, a 16-year-old girl had a lesion on her foot that was initial diagnosed as a spider bite infection (a common misdiagnosis of early MRSA skin infections). It didn't respond to initial treatment and MRSA was isolated on culture. The girl didn't have any history of contact with pigs or cattle, but had close contact with a foal. That foal had previously been in an equine hospital because of a wound infection, but the wound was not cultured. The same MRSA strain that caused the infection in the girl, however, was found in the foal's nose (the prime site for MRSA carriage by healthy horses). Fortunately, the girl's infection responded to treatment once treatment was adjusted for MRSA.

In some ways, this case is not too surprising, since we know ST398 MRSA can cause disease in people, and since it is found in horses, transmission from horses to people was likely inevitable. However, it's the first report of human infection with this strain associated with horse contact. MRSA exposure is a potential risk for anyone working with horses, since we know that this organism can be found in a small percentage of healthy horses. We don't have great information about how to prevent horse-human transmission, but simple things like only using antibiotics when needed and attention to hygiene (especially hand washing) when working with horses are presumably important factors.

More information about MRSA in horses can be found on the equIDblog Resources page.

This Worms & Germs blog entry was originally posted on equIDblog on 14-Jun-10.

Live every day like you have MRSA

I was giving a talk on infection control at a conference in Geneva a couple of days ago, and during a discussion with someone after the talk, I told them to "Live every day like you have MRSA." Not surprisingly, I got a bit of a strange look in response. I wasn't trying to say, "live your life to the fullest because you never know what will happen." Rather, I was trying to get the point across that healthcare workers in both the veterinary and human systems need to realize that at any point in time they could be carrying MRSA, along with various other harmful microorganisms.

People in patient care positions need to make the assumption that they are always a potential source of disease, and act accordingly while doing their jobs. If someone knew they were a carrier of a bug like MRSA, they'd likely do a better job with routine infection control practices such as handwashing. But, you rarely know whether you're carrying MRSA or not, and it's better to go on the assumption that you are and be diligent with your infection control measures.

The same basic concept applies to different situations, such as how people in the general population behave, and how they interact with other people and animals. In some ways, everyone should assume that they are carrying an infectious disease like influenza, and that every person or animal they encounter is carrying something infectious. (In reality, this is actually true, since everyone is carrying something potentially infectious in or on their body at any given time, it's just that most of the time it's not particularly serious or transmissible organisms).

There's a line between prudence and paranoia, and we don't want to create a population of germophobes who won't leave the house. However, we want to increase awareness so people do a better job of things like washing their hands and covering their mouths properly when coughing or sneezing. Assuming that you and everyone around you is mildly biohazardous maybe a way to do just that.

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MRSA, antibiotics and dogs

When multiple studies report the same results, it gets more and more convincing that the findings are true. This is becoming the case with antibiotic use as a risk factor for methicillin-resistant Staphylococcus aureus (MRSA) infections in dogs. Late last year, I wrote about a study of ours that identified prior antibiotic use as a risk factor in dogs for infections caused by MRSA versus those caused by methicillin-susceptible S. aureus. Recently, a similar study was published, with some similar results. This study (Magalhaes et al, Vet Res, 2010) compared dogs and cats and with MRSA infections to a group of dogs and cats with susceptible infections. They found that MRSA infections were associated with:

  • the number of antimicrobial courses
  • the number of days admitted to veterinary clinics
  • having had surgical implants

Additionally, animals with MRSA infections more often had had contact with people that had been in hospital, but the difference was not statistically significant.

That's two studies that identified antibiotic use as a risk factor for MRSA infection. It makes sense biologically, and it's likely that antibiotic use is an important driving force for MRSA infection in pets (like it is in people).

How do we reduce the likelihood of MRSA infections? It's pretty clear that reducing antibiotic use is a key factor. Antibiotics are important drugs and are certainly needed in many situations, but they're also prone to overuse and misuse. Here are some things that can (and need to) be done:

  • Only use antibiotics when necessary. Antibiotics are often used without evidence of a bacterial infection and in situations where bacterial infections are uncommon (e.g. urinary tract disease in cats, viral upper respiratory tract infections).
  • Use logical and prudent peri-operative antibiotic regimens. Only use antibiotics for surgeries when there are actually needed, and only for as short a period of time as possible.
  • Ensure that proper doses are given (and actually get into the animal). Unfortunately, underdosing (and overdosing) of antibiotics are not uncommon.
  • Promote more research regarding effective antibiotic treatment regimens. We often use much longer courses of antibiotics in pets compared to people, in part because we have no research data telliing us whether we can use shorter treatment courses.

Another thing to consider is the fact that these studies looked at factors for methicillin-resistant versus methicillin-susceptible infections. Therefore, a dog had to have an infection to be included. While certain things are risk factors for MRSA versus susceptible infections, there are other factors that increase the chance of any infection, and reducing these will also help reduce the risk of MRSA (and other) infections (i.e. if your dog doesn't get an infection in the first place, it won't have an MRSA infection).  One very important factor is proper management of underlying skin diseases, such as controlling atopy, flea allergy dermatitis and food allergy. Proper wound care, good veterinary clinic infection control practices and myriad other factors probably also affect the risk of infection in general. Further, good general preventive medicine practices, including overall healthcare and proper nutrition, play a role by decreasing the pet's susceptibility to infections.

Fighting antimicrobial resistance isn't easy or clear cut. There is unlikely a single measures that will turn out to be the "magic bullet." To limit the impact of resistant bacteria, we need to take a multifaceted approach, and we need a lot more information to figure out what specific measures should be emphasized.

Another Staphylococcus pseudintermedius infection

I'm not sure what to think about the recent increase in scientific papers about Staphylococcus pseudintermedius infections in people. This dog-associated bacterium has been well known for quite a while, and human infections have been sporadically reported, but it seems like there has been a big increase in reported cases over the past year.

The latest case, published in the Journal of Clinical Microbiology (Chuang et al 2010) describes a bloodstream infection in a 6-year-old boy. The infection was associated with an intravenous catheter site. The bacterium was initially misidentified as Staphylococcus aureus, a related bacterium that is more commonly found in people. It seems that the patient's history of having contact with dogs led to further testing of the bacterium. That's pretty surprising (and encouraging) from a few standpoints:

  • The attending physicians asked about pet contact. That's not always done.
  • The physicians recognized the potential for dog-human transmission of bacteria and considered the possibility that there was a misidentification by the lab. I'm quite surprised that they did further testing, since S. aureus is so common.

Unfortunately (as is commonly the case), they didn't take the investigation any further. It would have been nice for them to have tested the patient's dogs to see if they carried the same strain of S. pseudintermedius, to provide more evidence that the infection was truly from the dogs.

Concern has been raised before regarding the potential that S. pseudintermedius infections might be misdiagnosed as S. aureus, such that we don't know the true extent of the problems caused by the dog-associated bacterium. The ability of medical diagnostic labs to differentiate these two bacteria is something that needs to be investigated to help determine whether there may be more going on than we realize.

The increase in reports of S. pseudintermedius infections in the literature could also just be because infections that have always been occurring at a low level are being properly diagnosed, and people are bothering to write them up. The fact that people are still finding single cases of this infection noteworthy suggests that it's still a very uncommon condition. When you consider that the majority of dogs are carrying this bacterium, and millions upon millions of people have close contact with dogs on a regular basis, it's clear that people get exposed to this bacterium very often. The fact that infections appear to be so rare indicates that the risks to humans is likely quite low.

It's also possible that there truly has been an increase in these infections. It's hard to think of a reason why that might be the case. There's no evidence that the types of S. pseudintermedius have changed such that current strains are better able to infect people than older strains. Most likely, this is still a rare infection in humans that is often associated with dogs, but is of pretty low risk for the average dog owner. Regardless, continued study in the area is required, to make sure that this is not an emerging problem, especially when you consider that multidrug-resistant forms of this bacterium are also becoming much more common in veterinary medicine. Increased physician awareness about pet contact and zoonotic diseases is required to properly diagnose this and other potentially zoonotic diseases.

Skin infections in dogs: Stopping the downward spiral

A large percentage of advice calls that I get about methicillin-resistant staph infections in dogs are regarding skin infections. Skin infections (pyoderma) are a common problem, a leading cause of antibiotic use in dogs, and an often frustrating problem for vets and pet owners alike. One problem is that, unlike many other types of infections, skin infections are often recurrent. This frequently leads to an ongoing cycle of infection-treatment-resolution-infection-treatment-resolution... The net result is some dogs get treated very regularly and for long periods of time with antibiotics, and it's not particularly surprising that highly drug-resistant bacteria like MRSA or MRSP eventually become involved.

Normal, healthy, intact skin is an excellent barrier to bacterial infection. Various bacteria normally live on the skin but do not usually cause infection. Skin infections typically (if not always) develop in response to some underlying skin disease, such as flea allergy dermatitis, food allergy, atopy, Cushing's disease or hypothyroidism. Identifying and treating a skin infection is one thing. Identifying and treating the reason for the infection is another, and that is arguably the most critical component. Ignoring the underlying cause may not be the end of the world for a single infection, because proper treatment and a susceptible bacterium can result in a successful outcome, but ultimately ignoring the real problem can lead to a difficult-to-treat, resistant infections.

Any diagnosis of pyoderma should be accompanied by consideration of the underlying cause. If a cause is apparent, this should be treated (if possible). If a cause is not readily apparent, it should be investigated. By investigated, I mean a real search for the problem, not a cursory examination, half-hearted feeding trial and little more. There is almost certainly an underlying cause and, at the end of the day, time, effort and money are better spent on trying to identify the root issue rather than just throwing round after round of antibiotics at the dog. In some cases, the cause (while it's probably there) can't be identified, but it's definitely worth trying anyway.

If your dog has been diagnosed with a skin infection, ask why it happened. If there is not a clear answer, talk to your veterinarian about the best plan to identify the cause. If at all possible, follow through with the plan. It may include certain diagnostic tests (which cost money) or dietary restriction (which  takes effort), but it should be thought of as an investment in your pet's health, as well as a potential way to keep multidrug-resistant bacteria (some of which can infect people) out of the house, to save future treatment costs, and to keep your pet much more comfortable.

Survival of MRSA in swimming pools

Warm spells in early spring, like the recent warm spell in our area, inevitably lead to (premature) thoughts of summer, and for many people, this includes thoughts of spending time in the swimming pool. I've previously written about the presumably low risk of disease transmission from dogs swimming in pools, and common sense measures that can be taken to reduce any risks. Since more and more people and dogs are carrying resistant bacteria like MRSA, there are increasing questions about the potential for pools to be a source of transmission. A recent paper in the journal Clinical Pediatrics (Gregg & LaCroix, 2010) sheds some light on the issue.

In this study, the researchers obtained different types of swimming pool water (chlorinated water, saltwater, and biguanide (Baquacil) nonchlorinated water) from local pools. No MRSA was identified in any of the samples. They then inoculated the water samples with MRSA. They used a lot of MRSA - roughly similar to the amount that would be released from an MRSA abscess (and much, much greater than the amount that would be released from someone who was just an MRSA carrier). MRSA numbers were greatly diminished after 30 minutes and no MRSA was detected after 1 hour.

This study suggests that pools are likely not a significant source of MRSA exposure. Even with high-level contamination, MRSA died quickly. Presumably, there would be little MRSA shed by a person that was only a carrier, and when you consider the dilutional effect of a small amount of MRSA in a large volume of water, plus the bactericidal effects of treated water, the risks should be extremely low. Common sense would dictate that someone with an MRSA infection shouldn't go in the water because they could shed large numbers of bacteria, but this study suggests that the risks are probably minimal and short-term even then.

Bottom line: Don't worry about pools in terms of MRSA. Pools are a greater risk for certain causes of gastrointestinal disease like norovirus and Cryptosporidium. If you or your dog has an infectious disease, stay out of pools. If not, and you are otherwise healthy, then don't worry. There's always some risk of exposure to infectious disease, but it's very low. Life is full of risks and swimming in a pool is not a big one (at least from an infectious disease standpoint.  If you can't swim, that's a different story!).

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My dog has MRSP... Should I be concerned?

This is a question I get a few times a week. Because methicillin-resistant Staphylococcus pseudintermedius (MRSP) infections are becoming so common and people are aware of potential concerns regarding transmission of methicillin-resistant Staphylococcus aureus (MRSA) from pets to people, it's a logical concern.

Here's my basic thought process when answering this common question:

  • Staphylococcus pseudintermedius is very common on the skin and in the nose of healthy dogs. A large percentage of dogs are carrying this bacterium on any given day, and you can never tell who's a carrier by looking at them. Therefore, a large number of people are exposed to this bacterium on any given day.
  • Staphylococcus pseudintermedius is a common cause of infection in dogs, particularly skin infections.
  • Staphylococcus pseudintermedius can be found in the nasal passages of a small but appreciable percentage of healthy people, most likely acquired from their dogs.
  • Despite the frequent exposure, S. pseudintermedius infections in people are extremely rare.

So, the risk of getting a S. pseudintermedius infection from a pet is quite low. What about the methicillin-resistant version of this bug?

  • MRSP and the susceptible version differ by the presence of antibiotic resistance, and not necessarily anything else. Methicillin-resistance does not, to our knowledge, increase the virulence of this bacterium or make it more transmissible.
  • If transmission of S. pseudintermedius from pets to humans is very rare, and methicillin-resistance doesn't increase the risk of transmission, there should be no greater likelihood of someone getting MRSP from a dog compared to susceptible S. pseudintermedius.

So in the end there's not too much to be concerned about. Yes, there is a reasonable chance that MRSP can be passed between people and pets, but that's different than getting sick. Transmission of MRSP from healthy and sick pets to owners probably occurs on a regular basis, but since MRSP is not a normal bacterial inhabitant of people and it is not well adapted to cause disease in humans, not much happens.

But the disclaimer I always put in is "rarely doesn't mean never." The risks are very low, but they are not zero. While the odds of me picking up MRSP from a dog are very low, I'd rather not have an infection with a highly drug-resistant bacterium. Accordingly, the use of proper hygiene and infection control measures, particularly around an animal with an active infection, is always important. These measures include:

  • Frequent handwashing after contact with the pet.
  • Avoiding contact with the infected site.
  • Keeping the infected site covered with an impermeable dressing, whenever possible.
  • Reducing contact with the nose of the infected animal, since it may also be carrying the bacterium there. In general, reducing close contact (e.g. snuggling, nuzzling, hugging, kissing) during the period of infection is a good idea.
  • Regular washing (in hot water with hot air drying, whenever possible) of pet beds and other items that come into close and frequent contact with the pet.

Is all that overkill? Probably. But it's also an easy and practical plan, and a reasonable approach to reduce the already-low risks.

More information about MRSP is available on the Worms & Germs Resources page.

(Photo credit: John Haslam)

Big gun antibiotics in pets

Antibiotic resistant bacteria are a huge problem in human medicine, and they're an increasing problem in veterinary medicine. In pets, we are seeing dramatic increases in multidrug-resistant bacteria, some as a result of transmission from humans and some that are developing in animals. Regardless of the source, infections caused by resistant bacteria are a major problem. As resistance increases and we have fewer and fewer treatment options for some infections, the potential need to use certain antibiotics that are important for serious infections in humans ("big-gun" antibiotics) increases. This is a very contentious issue because concerns have been raised over the use of these drugs in animals and the potential impact on humans.

There are two extremes to the argument:

  1. These are critically important drugs in human medicine and they should never be used in animals.
  2. These drugs are used thousands of times a day in people and very rarely in animals, so the impact of periodic use in animals should be minimal, and failure to use them would result in animal deaths from potentially treatable infections.

I take the middle ground here. I am very concerned about antibiotic resistance (in pets and people) and I want to make sure that what I do does not have a negative impact on public health. I also realize that very rare and appropriate use of these drugs will realistically be unlikely to have any negative impact on public health, and that withholding treatment could cause animal suffering, death and prolonged infections that could be transmitted to their owners. The key, to me, is ensuring that use of these drugs is truly very rare and appropriate. At the Ontario Veterinary College, we have strict guidelines for use of "big-gun" antibiotics to try to ensure that there are used rarely and properly. For example, vancomycin can be used, but only when:

  • An infection is present and it is known that the bacterium is resistant to all other options and susceptible to vancomycin.
  • Local antibiotic administration or other types of alternative treatment are not options.
  • It's a serious infection that needs to be treated but it is treatable (i.e. no throwing a big gun drug at a patient that clearly has a terminal disease and does not have a realistic chance of surviving).
  • Approval is obtained from the Chief of Infection Control (i.e. me).

With this approach, we've only had 1 case where vancomycin was used, and that was in 2001. That's a pretty good record for a busy referral centre with a tertiary care caseload that sees "the worst of the worst." There have been a few instances when vancomycin was requested but with discussion and review of the case, better alternatives were identified. I'm certain that these guidelines have reduced the use of vancomycin and increased awareness of the problem, but have had no negative impact on patient care.

Antimicrobial resistance isn't going away. We can control it but not eradicate it. Scrutiny of antibiotic use in veterinary medicine is also not going to go away, and in some ways, that's a good thing. It should provide impetus to make sure that we improve how we use drugs, from the big guns down to our day-to-day drugs. Realistically, it's the regular use (appropriate use, overuse and misuse) of less exotic antibiotics that is having a bigger impact on antimicrobial resistance, and we need to pay attention to that as much as to the high-profile drugs.

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Staphylococcus (pseud)intermedius meningitis in a child

A paper in the International Journal of Infectious Diseases (Durdik et al 2010) describes a case of meningitis in an 11-month-old child caused by S. intermedius. (Presumably, the bacterium was actually S. pseudintermedius and they’re behind the times on identification of / nomenclature of this bacterium). This is the first report of this bacterium as a cause of meningitis in people, and obviously it’s a concern because of the potential severity of meningitis. Fortunately, the child made a full recovery with proper treatment.

S. pseudintermedius is a normal inhabitant of the skin and other body sites in dogs, and is found less commonly in cats. In this case, the child’s family owned a dog, but the dog lived outside and no direct contact was reported between the child and the dog. Indirect contact, such as someone bringing the bacterium in on their hands after touching the dog, would certainly be a possible route of transmission. Unfortunately, the authors of this study did not investigate the dog as the potential source and there was no attempt to isolate the same bacterium from the dog. The dog is certainly a likely source of infection here since S. pseudintermedius is not commonly found in people, and when it is, it is often associated with dog-contact.

There seems to have been an increase in reports of Staphylococcus intermedius/pseudintermedius infections in people lately. Reports are still very rare but there have been a couple in the past six months. That could be because there are more infections, but it could also be that people are just writing up the cases or that labs are getting better at identifying the organism. Overall, the number of apparent human infections caused by this dog-associated bacterium is very low.  While it is clearly a bacterium that can infect people, the risks to people in contact with pets is also very low. “Low” doesn’t mean “no”, however, and the very low but not negligible risk of S. pseudintermedius infection is just one of many reasons to pay close attention to good hygiene practices around pets, and ensure that your physician knows if you have pets.

More on pets and the risk of MRSA

We've seen reasonably good evidence of the potential involvement of pets in the transmission of methicillin-resistant Staphylococcus aureus (MRSA) for a few years, and a study recently published in the Journal of Hospital Infection (Loeffler et al 2010) sheds a little more light on the subject.

In this UK study, they tested 608 veterinary staff and pet owners in contact with pets that were carrying MRSA or methicillin-susceptible S. aureus (MSSA). MRSA carriage was identified in 12.3% of veterinarians that treated MRSA-infected animals and in 7.5% of their owners (although the chicken vs egg conundrum comes up, i.e. are vets that treated MRSA -infected pets more likely to have MRSA because they got it from the pet or because they already had MRSA and infected their patient?). These numbers are relatively consistent with a small number of other studies that have looked at these groups, and are higher than the expected carriage rates in the general population. This is highlighted by the results from people that had contact with animals only carrying methicillin-susceptible S. aureus, since MRSA was only identified in 4.8% of veterinary staff and 0% of owners in this group. Veterinary personnel were significantly more likely to carry MRSA than pet owners. As expected, virtually all MRSA from people and pets in the study were the predominant strains present in human hospitals in the UK.

We shouldn't fear MRSA or our pets, but we should respect the potential for infection and act accordingly. Mainly, this involves basic practices like:

  • Good hygiene: washing hands regularly after handling pets
  • Avoiding contact with infected body sites in pets, and preventing pets from having contact with infected body sites in people
  • Prudent antibiotic use in both veterinary and human medicine
  • Proper and timely diagnostic testing to identify MRSA infections, to permit proper treatment and earlier implementation of appropriate infection control practices.

Ultimately, MRSA in pets is a human-borne disease. Most pets that have MRSA presumably acquire it from a close human contact, so efforts at controlling MRSA in pets need to be directed at both the pet and human aspects. Uncontrolled MRSA in people will lead to increased risk for pets, and for pets to be a source of subsequent human infection.

Image: Seven-month-old British Shorthair (photo credit: Tamila Aspen)

Risk factors for MRSA in dogs

A recent study just published in the journal Emerging Infectious Diseases evaluated risk factors for dogs having an infection with methicillin-resistant Staphylococcus aureus (MRSA) versus methicillin-susceptible S. aureus (MSSA). This study, headed by Dr. Meredith Faires, compared dogs with MRSA versus MSSA infections from three different veterinary referral hospitals in Canada and the US. Among the more important findings were the following:

  • Staying in a veterinary hospital was not a risk factor for MRSA infection, reinforcing the notion that this is predominantly a community-associated disease in dogs (meaning it typically develops in dogs in the general population).
  • Most infections, in both the MRSA and MSSA groups, were skin infections. While serious deeper infections can and do occur, skin and ear infections are very common.
  • Prior treatment with antibiotics was associated with development of MRSA versus MSSA infections. Dogs that received any antibiotic within 90 days were approximately 3.8 times as likely to have MRSA versus MSSA infection. Dogs treated with drugs from the fluoroquinolone class of antibiotics were 4.6 times as likely to have MRSA versus MSSA infection.

The association between prior antibiotic use and development of a resistant (i.e. MRSA) infection is not surprising, but it is important to document these events and to be aware of them. Antibiotics are critically important drugs in veterinary and human medicine. They save countless lives, but are also overused and misused frequently, and resistance is a critical problem. Studies such as this demonstrate the need for prudent antibiotic use - use them when needed, but use them properly.  Don't use them when a bacterial infection is not present or unlikely to occur.

The study can be downloaded by clicking here. More information about MRSA in available on the Worms & Germs Resources page.

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The good and bad of pet therapy

.An article about a therapy dog demonstrates some good points of these programs and places to improve. The story is about "Taco", a Chihuahua involved in pet therapy at the Livingston Regional Hospital (Tennessee). The obvious benefit of the program is highlighted by the owner's comment "She creates smiles when there were none." There are definite social and emotional benefits of pet therapy. There are also some potential health benefits, although the research on that isn't the strongest. On the downside, there are disease transmission concerns. These can be greatly reduced through attention to some simple procedures, but this article describes a number of concerning yet common problems:

"(Taco) greets each patient (ones who are comfortable enough to have her in their lap) with kisses on the nose."

  • Being allowed to lick patients has been shown to be a risk factor for visitation dogs acquiring MRSA. Being allowed to like the nose is about as good of a model of MRSA transmission as you can develop, because the nose is the number-one site where this important bacterium lives. This type of licking can also transmit various other infectious agents to this compromised hospital population. Licking is an unnecessary behaviour that should not be permitted because it can be associated with infectious agent transmission.  Not permitting licking does little to decrease the value of visitation.

"(Owner Gerry) Cotnoir has had Taco since she was 9 weeks old.  She worked at Bethesda [Health Care Center) in Cookeville then and brought Taco with her to work every day. "She got used to people at an early age,""

  • Socialization of dogs is important, but a hospital is not the place to do this. Only dogs older than 1 (and ideally older than 2) years of age should be in hospitals. Young animals are more likely to bite or scratch; not necessarily from aggression but also from playful or excited behaviour. Young animals also have much higher rates of shedding of various infectious agents such as Campyobacter.
  • People in hospitals should not be bringing pets to work. Animals that are in hospitals should be there for formal, structured, short-term, properly observed and properly scrutinized visitation activities. That's not the case when someone brings a pet to work. A hospital is not a doggie day-care, although some people use them as such, with the occasional visit of a patient to explain why they are there.

The hospital's infection control personnel have approved the use of Taco in the Livingston facility, but you have to wonder how much they investigated the issues. There are clear guidelines for hospital therapy programs which aren't being followed here. Hopefully other important aspects of the guidelines, especially hand hygiene, are being followed. It's likely this is a situation where people don't understand the issues and don't realize that there are both concerns and resources to help them out.  Any facility that has, or is thinking of having, a visitation program, should be aware of these guidelines, plus other information from reputable groups such as Delta Society.

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Staph pseudintermedius infection in a person

When I talk about methicillin-resistant Staphylococcus pseudintermedius (MRSP), I usually say that the human health risks are low because human infections are very rare. However, rare doesn't mean it can't happen, as demonstrated by a case report entitled "Beware of the Pet Dog: A Case of Staphylococcus intermedius Infection" published in the American Journal of Medical Sciences (Kempker et al 2009).

This paper reports about a post-operative sinus infection in a 28-year-old woman. Cultures were taken and the bacterium was initially misidentified as a coagulase-negative Staphylococcus. It was then misidentified as S. aureus, and finally determined to be S. intermedius. In reality, that's probably another misidentification because the bug almost certainly was truly S. pseudintermedius. (It's become clear over the past couple years that S. intermedius is basically non-existent in dogs and that what has been called S. intermedius in the past is truly S. pseudintermedius).

It's important to remember that human infection with S. pseudintermedius is a rare event. Whenever you see a single case reported, you know it's a pretty uncommon or novel event. Further, this was a post-operative infection, not a spontaneous infection occurring in a low-risk person. At the same time, we need to make sure we don't completely ignore the potential risks. While the risk of transmission of S. pseudintermedius (including MRSP) seems to be very low, we shouldn't ignore it completely. Isolation and other strict measures aren't indicated when dealing with a pet with S. pseudintermedius infection, but general attention to basic hygiene practices and avoiding contact with the infected site is still a good idea.

MRSA outbreak in Dutch horses

At the ongoing ASM-ESCMID conference on methicillin resistant staphylococci in animals, Dr. Engeline van Duijkeren of Utrecht University (The Netherlands) presented a study on an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in their equine hospital.

From 2006-2008, several horses that underwent surgery at their hospital developed MRSA infections.  MRSA was also isolated from some healthy horses and personnel at the clinic. Early in the process, the hospital was closed for a thorough disinfection and the outbreak stopped, however another outbreak occurred later.  Further study again found people in the clinic that were MRSA carriers. Close to 15% of people in the hospital who handled equine patients were MRSA carriers, which is really astounding when you consider that less than 0.1% of the general population in the Netherlands carries MRSA. When they started testing horses coming into the clinic, they found that 9.3% of horses were carriers when they arrived. Weekly sampling of all hospitalized horses over a five-week period determined that 43% of all horses in the hospital carried MRSA at one point or another during their stay. Additionally, 53% of environmental surface samples were positive for MRSA, which is really not surprising if that many people and horses are carriers.

If horses keep coming into a facility carrying MRSA and people keep getting colonized, MRSA is hard to control. These experiences led the equine hospital at Utrecht to implement more stringent infection control practices to try to contain the problem, but the high MRSA rate in their referral population is going to pose a continual risk.

MRSA outbreaks in horses aren’t new. They’ve been reported by a few hospitals (including ours) and occur in many, many, (many!) more without ever being published. Since MRSA is present in the horse population, equine hospitals are at continual risk of MRSA outbreaks. If a large percentage of horses in the general population are carriers, the risk of outbreaks is higher.

MRSA is clearly a problem in horses in many areas. It’s important to realize that it’s a problem in the general population, not just horses in hospitals. Equine hospitals can amplify the spread of MRSA, but ultimately a lot (if not most) MRSA-positive horses originate from farms, not clinics or hospitals. Equine hospitals need solid infection control programs to reduce  the risk of outbreaks, but the risk will never be completely eliminated. Farms need good infection control programs to reduce the risk of spread of MRSA between horses and between farms, as well as from horses to people (and back). Antibiotics need to be used prudently since antibiotic use is a risk factor for MRSA carriage and infection.

More information about MRSA in horses can be found on the equIDblog Resources page.

This Worms & Germs blog entry was originally posted on equIDblog on 26-Sep-09.

Good drugs in Saskatoon

More from the ASM-ESCMID MRSA in animals meeting…

Dr. Joe Rubin presented some data on antibiotic resistance in Staphylococcus aureus bacteria from dogs and people in Saskatoon, Saskatchewan (Canada). The bacterial isolates came from dogs carrying S. aureus and from dogs infected with MRSA. When you look at the resistance patterns of the S. aureus isolates from the carrier dogs (these are an indicator of what’s around in the general population, and they can cause infections given the right circumstance), resistance was uncommon. Multidrug resistance was present in the methicillin-resistant S. aureus (MRSA) isolates, as expected.

Saskatoon’s an interesting area in terms of resistant bacteria. Various studies from the University of Saskatchewan have reported very low antibiotic resistance rates in bacteria from animals. Certainly, they have some problems like everywhere else, but I find some of their data quite remarkable. They can have a lot more confidence in the use of various first-line antibiotics compared to other regions where resistance is more common and drug options are more limited. I’m not really sure why this is the case.

  • Maybe it has to do with the fact that there is less animal movement between Saskatchewan and other regions where there are more resistance problems.
  • Maybe the low population density in Saskatchewan plays a role.
  • Maybe multidrug resistant bacteria don’t like the frigid Saskatchewan winter (or the fact that there’s no NHL team in the province).
  • Maybe they use antibiotics in animals in a much more controlled manner.

Trying to figure out why resistance rates in Saskatchewan tend to be lower would be useful because it might provide some information about how to reduce the risks in other regions.

So, if you’re in Saskatoon and your pet gets an infection, take some consolation in the fact that there’s probably a lower risk that you’re dealing with a resistant bacterium and that your first-line antibiotics will probably work.

MRSA prognosis in dogs

People sometimes panic after they hear that their pet has been diagnosed with an MRSA infection. ("Dr. Google" doesn’t help because if you search "MRSA" you can come up with a lot of scary information). However, it’s very important to understand that just because MRSA is involved, it does not mean that an animal (or person) has an untreatable infection. In fact, there are typically at least a couple of different treatment options available. That’s not to say that MRSA infections are of no concern, because they certainly are, but you have to maintain some balance.

Two studies presented at the ASM-ESCMID conference on methicillin-resistant staphylococci in animals re-inforce this. Dr. Andy Hillier from The Ohio State University presented a small study looking at 11 dogs with MRSA infections, including skin infections, surgical site infections, soft tissue infections and an ear infection. One dog was euthanized before treatment was started. All of the other 10 dogs survived. Aggressive treatment was needed in some cases, including some that required surgery to remove surgical implants or severely infected tissue. Still, they survived.

Similar results were presented by Dr. Meredith Faires from the University of Guelph. As part of one study, she reported survival of 42/45 (93%) of dogs with MRSA infections. A large percentage of dogs in that study had MRSA skin infections, which would not typically be expected to cause death, so it’s important to consider what types of infections are involved. Studies of invasive infections (e.g. infections of deeper tissues, infections of the bloodstream) presumably carry a much worse prognosis.

Regardless, these two studies provide more evidence that while MRSA can be bad, it’s not automatically a death sentence. With prompt diagnosis and proper treatment, a large percentage of infected dogs (and presumably cats as well) will survive. Prompt diagnosis and proper treatment are the key.

Live from London: MRSA in Ohio

I'm in London (UK) for the ASM-ESCMID conference on methicillin-resistant staphylococci in animals: veterinary and public health consequences. I’ll provide various updates on interesting presentations over the next few days.

Dr. Armando Hoet from the Ohio State University (OSU) presented data on MRSA screening of dogs admitted to the OSU Veterinary Teaching Hospital. They sampled a subset of dogs admitted to the hospital every month over the course of a year.

  • 5.7% of the dogs were identified as MRSA carriers. That’s a pretty impressive (and concerning) number. We know that a small percentage of dogs and cats in the general population are positive, but I’ve generally assumed the rate of carriage to be around 1-4%. However, you have to consider the study population whenever you look at numbers like this. Sixty-eight percent of the positive dogs were referral cases, meaning they had had previous contact with the veterinary healthcare system, may have been treated previously with antibiotics and may have had other diseases that increased the risk of MRSA.
  • Ownership by people in the human or veterinary healthcare fields were risk factors for infection.  This is not very surprising since such owners would be more likely to pick up MRSA at work and bring it home to infect their pets.

Hopefully the true percentage of dogs in Ohio carrying MRSA is lower than this. Presumably, the rate of MRSA carriage by healthy dogs that are not owned by high-risk people is quite a bit lower. Regardless, it shows that MRSA can be found in a reasonable percentage of animals in the study area (as well as presumably other areas) and that good infection control practices are needed in veterinary hospitals to reduce the risk of transmission.

More information about MRSA can be found in on the Worms & Germs Resources page.

Methicilin-resistant Staphylococcus schleiferi in pets

When it comes to methicillin-resistant staphylococci in pets, MRSA (methicillin-resistant S. aureus) gets most of the attention. That's fair since it's emerging as an important health problem, and can be transmitted between pets and people. Now another staph, MRSP (methicillin-resistant S. pseudintermedius) is getting more attention, and it's actually a more common cause of infections in dogs and cats compared to MRSA. There are also some other methicillin-resistant staph that get much less attention. One is methicillin-resistant S. scheliferi (MRSS).

There are actually two different subspecies of this bacterium, S. schleiferi subsp. coagulans and S. schleiferi subsp. schleiferi. Staphylococcus schlieferi subsp. coagulans is the coagulase-positive subspecies. (Coagulase testing is one of the main ways staph species are classified.) Sta[hylocccus schleiferi subsp. schleiferi is coagulase-negative. In general, coagulase-negative staph are considered to be minor concerns and rare causes of disease other than in sick, compromised individuals in hospitals. However, it looks like S. schleiferi subsp. schleiferi is an exception to that rule, as it is able to cause disease in otherwise healthy dogs and cats.

Both S. schleiferi subtypes predominantly cause skin and ear infections. As with other staph, methicillin-resistance is a concern and is increasing. Methicillin-resistant S. schleiferi (MRSS) rates appear to be increasing, which is a concern because methicillin-resistant staph infections are harder to treat due to their resistance to many antibiotics.

One factor that limits our knowledge of the role of MRSS (and really, S. schleiferi in general) in disease is the fact that many, if not most, diagnostic laboratories don't try to differentiate it from S. pseudintermedius because the two species are very similar. (Sometimes, labs don't even try to differentiate any of the coagulase positive staph, including S. aureus).

While MRSA in pets is a public health concern, there is probably much less to fear from MRSS. Staphylococcus schleiferi infections in people are quite rare and there is currently no indication that pets are an important source of human infection. However, given our limited knowledge of this bacterium, it's wise to take some degree of precaution around animals with MRSS infections, particularly basic measures such as avoiding direct and indirect contact with infected sites, and good handwashing habits. These are the same general recommendations for pets with MRSP, and more details about this are available on the Worms & Germs Resources page. 

MRSA and vancomycin in dogs

Methicillin-resistant Staphylococcus aureus (MRSA) infections are an emerging problem in dogs and cats. They're a huge problem in human medicine, and the emergence of MRSA in pets can be directly traced to the spread of MRSA in people.

A big problem with MRSA infections is that they can be difficult to treat because they can be resistant to many antibiotics (not just methicillin). This complicates treatment, but it's important to remember that most MRSA infections are treatable.

An important concern with MRSA is that it may lead to unnecessary veterinary use of drugs that are critically important for treatment of life-threatening infection in humans. Vancomycin is an antibiotic that is occasionally used to treat MRSA infections in dogs, although I've never had to use it. I stumbled across a supposed "veterinary information website" today that stated vancomycin is the main treatment for MRSA in dogs. It quickly became clear the authors had no clue about the topic, because they kept calling MRSA a virus (always scrutinize the source of information, especially on the internet). Information like this doesn't help with prudent use of drugs like vancomycin.  It's important for pet owners and veterinarians alike to realize that these "big-gun" antibiotics (such as vancomycin) are rarely needed for MRSA infections in dogs and cats. There are almost always other, and usually better, options.

Vancomycin is also sometimes inappropriately used in animals, which can lead to worsening of infection.  For example, if vancomycin is mistakenly given orally, the drug is not absorbed from the intestinal tract and therefore has no chance of fighting infection elsewhere on the body.

In general, MRSA infections are quite treatable. Survival rates tend to be high and, with proper treatment, should be no lower for MRSA infections versus infections caused by susceptible strains of S. aureus. A comparison of MRSA versus susceptible S. aureus infections presented last year reported no difference in survival rates, with an overall survival rate of >80%. The key is diagnosing the infection early and getting started on the right treatment. That means getting cultures done earlier, rather than later.

While increasing antibiotic resistance may lead to more need for "big-gun" antibiotics in some cases, we need to act prudently and restrict their use to situations in which they are absolutely required. Use in animals needs to be very prudent to avoid contributing to antibiotic resistance in people. Inappropriate use in animals could lead to more calls to restrict veterinary access to various drugs, which could threaten treatment of other animals with other types of infections.

Don't confuse "big-gun" antibiotics with the best treatment.

More information about MRSA can be found on the Worms & Germs Resources page.

MRSA testing and false advertising

I received a flyer from Zoologix, a company that offers various (typically unvalidated and unproven) PCR tests for animals. The flyer headline was "Pets can carry MRSA - but testing can help."

Testing in certain situations is useful, but this is almost always limited to diagnosis of animals with active infections (i.e. they're sick). PCR is not a good way to make such a diagnosis, because the test doesn't tell you anything about the bacterium's susceptibility to other antibiotics. Screening of pets just to determine whether or not they carry MRSA is rarely needed, and currently there is no evidence that PCR is a reasonable test for this.

There are no validated PCR tests for MRSA in animals. We looked at using a human test in horses and it failed miserably. There are validated tests for use in people, and they are quite good: they accurately identify MRSA and differentiate it from other methicillin-resistant staphylococci and from methicillin-susceptible S. aureus. That's critical, because you have to know what a positive test really means.

I called the company and asked what the test actually detects. They said it detects the mecA gene, the gene that confers methicillin-resistance to staphylococci such as S. aureus. However, this gene can be present in other staphylococci that can be found in many  healthy dogs and cats (10-30% in some studies). It does not actually detect MRSA and a large percentage of samples that give positive results will be false positives. The tests that are used in humans are specifically designed to look at two things in combination: whether S. aureus is present and whether it has the mecA gene (methicillin-resistance). This is the right approach because it excludes all those other false positives. Detecting mecA alone is completely useless. It's interesting that the flyer states "PCR testing is fast, effective and accurately differentiates MRSA from other bacteria - even other Staph strains." Based on what the company told me over the phone, with regard to the test they're advertising, that's a blatant lie.

This is an example of a combination of bad science and bad ethics. This company has no business marketing this test. It's false advertising, because the test isn't an MRSA test. Their justification for using it is similarly weak. Anyone thinking about using this test should run away quickly! The issues with this test (and others) should also be considered when deciding whether to use this company for any tests.

More (and accurate) information about MRSA can be found on the Worms & Germs Resources page.

MRSA and atopy

A recent question: "If a dog has severe atopy that is poorly managed, and is colonized w/ MRSA  (superficial dermatidis on neck ventrum and axilla) are repeat infections w/ MRSA likely, if the allergies cannot be controlled?"

Dogs with atopy (allergic skin disease) are prone to opportunistic infections because of the abnormal skin "environment" and trauma from licking and scratching. Damage to the skin creates the opportunity for various bacteria to cause infections, including some bacteria that may usually live on normal skin without causing problems.  Most commonly, staphylococci are involved, and this may include skin infections with MRSA (methicillin-resistant Staphylococcus aureus). The likelihood that a dog will develop an MRSA skin infection depends on the likelihood of exposure to MRSA. If the dog is already a carrier (i.e. has MRSA in its nose or intestinal tract), the odds are greater because exposure of the skin to the bacterium is more likely. If the dog is owned by someone with MRSA or someone who visits human hospitals, the risks are likely greater as well because of the increased chance of MRSA exposure via the owner.

For most dogs, the risk of MRSA infection is not high. Fortunately, dogs that are MRSA carriers are typically only carriers for a short period of time. They usually eliminate MRSA carriage naturally within a couple weeks, if re-infection is prevented. So, for a dog that is a carrier or has an MRSA skin infection, if carriage is eliminated and the infection is properly treated, the risk of subsequent MRSA infections should be quite low, as long as there is a not a high likelihood of re-exposure.

Dogs with chronic skin disease should not visit human hospitals in order to reduce the risk of developing MRSA infection. If such a dog is owned by someone who is infected or colonized with MRSA, particular attention should be paid to handwashing to reduce the risk of transmission of MRSA to the dog. In situations other than these, recurrent MRSA infection is probably not a risk if basic hygiene practices are used. If an MRSA infection is present, it must be properly treated - sometimes apparently "repeated" infections are actually infections that were never completely eliminated in the first place.  A key component of management of dogs with atopy (and other chronic skin conditions) is getting the atopy under control so that there is less chance of secondary bacterial infection.

More information about MRSA in pets can be found on the Worms & Germs Resources page.

Dog bites and MRSA

There's been a lot of talk (hype) in the press about pet bites and MRSA (methicillin-resistant Staphylococcus aureus). This relates to a paper in Lancet Infectious Diseases regarding infections associated with pet bites. Some press articles are more sensational than others, but most are taking the bite infection paper and building in unrelated comments about MRSA in animals to make it seem like there's a major MRSA dog bite epidemic underway.

I realize that MRSA is a hot topic that is easy for reporters to latch onto, but the problem is that the actual research related to MRSA is being taken out of context (and blown out of proportion). MRSA was certainly mentioned in the paper, but it was not the focus of the research nor do the authors play up concerns about pets as a source of MRSA infections. Nevertheless, the impression people are getting from many news articles is that there is rampant MRSA transmission by infected pets.

Is MRSA infection a potential concern after a dog bite?

  • Yes, but more because of the bite itself than the particular dog.  MRSA infections that occur after a dog bite are probably the result of contamination of the wound with MRSA from the person's own nose or from another person, for example during a visit to their physician/clinic/hospital. It's possible for MRSA to be in the mouth of the dog and for it to be transferred to the wound during the bite, but that's pretty unlikely. The person bitten or someone treating the wound is a more likely source of the bacterium. So, the bite was the ultimate "cause" of the MRSA infection, because the infection probably wouldn't have developed without that break to the body's normal defensive barriers (i.e. the skin), however the "source" of the infection was (in most cases) NOT the animal.  The same kind of infection could have happened with any similar type of trauma.

What should I do if I'm worried about MRSA and dog bites?

  • Worry more about dog bites than MRSA. Bites themselves are major problems, even if MRSA is not involved. The degree of trauma can be significant, and a variety of bacteria can cause serious bite infections, not just MRSA.
  • Take measures to reduce the risk of being bitten, both in terms of how you handle and train your dog and how you interact with other dogs.
  • If you are bitten, immediately clean the wound as thoroughly as possible. If the bite is over a joint, tendon (e.g. wrist/ankle), prosthesis or genitals, if there is significant trauma or if you have a weakened immune system, you need to see a physician. If you have any other concerns, get examined by a physician promptly.

More information on MRSA in animals can be found on the Worms & Germs Resources page.

EFSA Statement on MRSA in animals and food

The European Food Safety Authority, along with the European CDC and European Medicines Agency, have released a report about methicillin-resistant Staphylococcus aureus (MRSA) in livestock, pets and food. There's nothing too earth-shattering in it, and nothing more than what we've been saying all along, but some of the points are worth repeating.

  • While food may be contaminated with MRSA, there is currently no evidence that eating or handling MRSA-contaminated food leads to increased health risks in people.
  • Pets can be infected with MRSA, first acquiring it from people but then potentially transmitting it back to humans.
  • Transfer of MRSA to humans from companion animals and horses is difficult to control. (I don't agree with that). Basic hygiene measures are important before and after animal contact. Additionally, avoiding contact with nasal secretions, saliva and wounds is ideal.
  • Prudent use of antibiotics in animals should remain a key measure and monitoring of antibiotic use in animals should be performed to identify unnecessary use.
  • Drugs of last resort for the treatment of MRSA in humans should be avoided in animals.

Preventing infections in the home

There is a nice, concise commentary in the most recent issue of the Canadian Medical Association Journal about preventing infections in the home. It covers three important organisms: MRSA, Clostridium difficile and vancomycin-resistant enterococci (VRE). An excellent aspect of this particular commentary is its relatively low-key approach, with an emphasis on routine, basic practices such as hand hygiene. It also includes some comments about pets that are similarly well-balanced and go along with a lot of what we've been saying on Worms & Germs Blog. For example, in discussing MRSA, they state:

"Because domestic pets may serve as a reservoir of MRSA, hands should always be washed thoroughly with soap and water after contact with animals or their feces. In cases of outbreaks within a family of an infection caused by community-associated MRSA that cannot be arrested, a colonized pet may need to be temporarily removed from the home. However, it may be prudent to re-emphasize the importance of personal hygiene before taking such a drastic measure."

Overall, it's a commentary you might find useful. It can be downloaded by clicking here.

Another reason to stay away from surgeons

As a veterinary internist, I’m always looking for a good excuse to harass veterinary surgeons, and a recent study we performed with Dr. Lee Burstiner (an aspiring surgeon but a good guy anyway) at the 2008 American College of Veterinary Surgeons (ACVS) conference gives me more ammunition. This study is being presented today at the European Conference of Clinical Microbiology and Infectious Diseases in Helsinki.

A few recent studies have shown that veterinarians seem to be at higher risk for methicillin-resistant Staphylococcus aureus (MRSA) carriage, likely because of their frequent contact with animals that can also carry MRSA. As part of the study at the ACVS conference, attendees provided nasal swabs (because the nose is the main site of MRSA carriage) on a voluntary basis, and filled out a questionnaire about various potential risk factors. MRSA was isolated from 17% of participants, an astounding number considering that in the general population only about 1-3% of people carry MRSA.

In previous studies of MRSA in veterinarians, including veterinary internists, equine general practitioners and swine veterinarians, it has been equine or swine veterinarians that most often harbour MRSA in their noses. Interestingly, in this study, there was no difference between equine and small animal (e.g. dog and cat) vets, which is perhaps due in part to the steady increase in MRSA carriage by dogs and cats internationally. This is one more piece of evidence indicating that MRSA exposure is an occupational risk for veterinary personnel. Colonized personnel may be  more likely to develop MRSA infections, and are also at risk of transmitting MRSA to their patients (and possibly also their family members). This reminds us yet again of the need for good general infection control and hygiene practices in veterinary medicine.

It is truly astounding that MRSA colonization is so common in veterinarians. This is a consistent result among a few different studies now, and veterinarians may be one of the highest risk groups (if not the highest risk) for MRSA colonization. Why is this the case? Why is the prevalence not as high in human healthcare personnel? From where is the MRSA coming?  From the patients presumably? How do we control it? What are the implications for the health of veterinary personnel and their families? These are just some of the many important but unanswered questions.

All this being said, you don't need to (and shouldn't) actually consider veterinary surgeons (or veterinarians in general) biohazardous, nor should you avoid using veterinary specialists because of concerns about MRSA. MRSA is a problem in veterinary medicine in both referral and general practices, and studies like this show the need for further research to determine why this is the case, as well as the need for general improvement in infection control in veterinary medicine.

More information about MRSA in animals can be found in on the Worms & Germs Resources page. Information on MRSA in horses can be found on our sister site, equIDblog.


MRSA strains found in pets

Methicillin-resistant Staphylococcus aureus (MRSA) is an important  (and high profile) cause of disease in people, and an emerging problem in animals. Evaluating the types of MRSA that we find in pets can help us understand what is happening with MRSA in pets and why.

A few different studies have evaluated the types of MRSA found in pets, using different molecular typing methods. The common result from all these studies is that the MRSA types found in pets are typically the same as those found in people in the same area. Even in different countries where there are different MRSA strains, the strains most commonly found in people are the same as the ones most commonly found in pets. Also, as the types of MRSA found in people in different regions change, so do the types found in pets.  For example, USA300 (which can be a particularly nasty strain of MRSA) emerged a few years ago as a leading cause of MRSA infections in people in the general population (i.e. community-associated MRSA) in the US.  Shortly thereafter, we started to see this strain in pets too. As USA300 began to crop up in people in Ontario, we also started finding it in pets. These results strongly suggest that MRSA in pets is closely related to MRSA in humans, and that most MRSA infections in pets ultimately started off in a person. Remember, though, that pets can still transmit MRSA once they've been infected.

It's inevitable that we will see more changes in MRSA types in people in the future, and it's almost certain that these changes will then be reflected in animals. In some ways, we can use humans as sentinels for what we are going to see in pets. By monitoring what is happening with MRSA in people and how it is being addressed, we can perhaps figure out the best (and worst!) ways to address the problem in animals.

More information about MRSA in pets can be found on the Worms & Germs Resources page. Information about MRSA in horses can be found on our sister site, equIDblog.

Pet therapy and patients with multidrug resistant bacteria

I received this question on hospital visitation animals today...

For patients who are on contact precautions for a multidrug resistant organism, what other than hand hygiene could be suggested?  I am currently rewriting our hospital infection control policy related to pet therapy and visitation with clients with a MDRO [multidrug resistant organism]. I was thinking that visitation of clients with a MDRO should not be allowed??? Any advice?

I am surprised at how often I get asked about pets and patients with multidrug resistant infections. These patients are typically isolated and managed with "contact precautions". The goal of these precautions is to reduce the amount of contact between the infected patients and other people (staff and patients) and includes the use of barriers (e.g. gowns, gloves) to reduce the risk of disease transmission when contact must occur. If the goal is to reduce contact, we shouldn't be allowing patients with these infections to have contact with pets. Pet therapy animals usually visit a large number of patients in the hospital, and we don't want them transmitting an infection to the other patients they visit. Pets are also accompanied by people (their owners), who we don't want to  expose to infection and/or to transmit infection to other patients. So, visitation of these high-risk patients by animals should not be allowed. Animal visitation can have very positive effects and its unfortunate that people with multidrug resistant infections should be restricted from these programs, however it's for the greater good of other patients in the hospital, as well as the pet and its owners.

More information about pet therapy programs can be found in our hospital visitation archives.

Image from:
(It's a cute cartoon. I just have to ignore the fact that the dog is on the bed (i.e. the patient's living space) without being on a barrier such as towel or drape.)

Dirty hands, Dirty therapy dogs?

A study published recently in the Journal of Hospital Infection (Lefebvre & Weese, 2009) looked at contamination of the haircoat of animals used in hospital visitation programs. In the study, Dr. Lefebvre petted animals that were going into a hospital and we cultured her hands.  Then when the dogs finished their visits she petting them again and we re-cultured her hands.  We tested for MRSA and Clostridium difficile, two important causes of hospital-associated infections. The goal was to see if the dogs' coats could become contaminated, presumably by patients' hands, during regular visits. The dogs' paws were also tested before and after to see what they picked up walking around the hospital.

After being in the hospital, one dog (4%) was found to have C. difficile on its feet. The strain that was recovered (ribottype 027/NAP1) is a strain of great concern, being it has caused outbreaks of illness internationally. The fact that there was C. difficile on the dog's paws, which was presumably picked up from the floor in the hospital, isn't exactly surprising. It shows that contact with dogs' feet (e.g. shaking a paw) could be a source of exposure to people in hospitals, and at home, and that dogs could be exposed to C. difficile after hospital visits by licking their paws. We previously demonstrated in another study that visitation dogs are at high risk for picking up C. difficile during visits.

The more important aspect of the study was what ended up on Dr. Lefebvre's hands after petting the dogs - a very common type of contact with dogs in hospitals and at home. She picked up MRSA from the coat of one dog (4% of dogs overall) after it had been in the hospital. The dog was not an MRSA carrier, and it did not have contact with anyone known to be carrying MRSA during its visit. Presumably, there was someone in the hospital that was an unknown carrier. If MRSA was on the person's hands, they could have transfered the MRSA to the dog's coat. The important part is that this MRSA was then able to spread to someone else's hands (Dr. Lefebvre's, in this case). This is a potential route of transmission of MRSA to patients during hospital visitations, and to other people these dogs might encounter outside of hospitals. The same thing could presumably happen with other infectious agents, including bugs like norovirus and influenza. These can't infect dogs, but dogs could potentially be short-term vectors of these viruses and spread them around a hospital.

The good thing about all this is that some basic guidelines can greatly reduce the risk of transmission:

  • Patients should wash their hands  or use an alcohol-based hand sanitizer before  (to reduce the risk of depositing something on the pet's coat) and after (to reduce the risk of picking something up from the pet's coat) touching a pet.
  • Pets should be kept off beds unless a disposal/washable barrier (e.g. drape, towel) is kept between the pet and the bed sheets, to prevent dirty feet from infecting the patient's living space/clothes/sheets.
  • People should not "shake-a-paw" with pets in hospitals.

All these precautions can be taken without compromising the benefits of hospital pet visitations. More details about guidelines for hospital visitation aniamls can be found in an earlier post. More information about Clostridium difficile and MRSA can be found on the Worms & Germs Resources page.

Should I isolate my dog with MRSP/MRSI?

Methicillin-resistant Staphylococcus pseudintermedius (MRSP, sometimes misidentified as methicillin-resistant S. intermedius (MRSI)) is an increasing problem in dogs and cats. This highly drug-resistant bacterium is a particularly problem in skin and ear infections, and the number of infected animals appears to be increasing significantly. A related bug, methicillin-resistant S. aureus (MRSA) has been a major problem in people for decades, and MRSA is now being found with increasing frequency in animals as well. Sometimes people get confused when they are dealing with methicillin-resistant staph, and it's important to realize some of the differences between these two related bugs:

  • MRSA is a huge problem in people and can be transmitted between animals and people. The role of animals in human disease is unclear, but there is concern that people can develop infections due to contact with infected or colonized animals.
  • MRSP is rarely identified as a cause of infection in people. Transmission of MRSP between animals and people has been reported. However, this is much less concerning than with MRSA because people are much less likely to carry, transmit or develop infection from MRSP than MRSA.
  • The recommendations that have been made for management of animals with MRSA largely involve improving general household infection control practices. These guidelines are only based on expert opinion (i.e. there are no studies (yet) to back them up), but they are reasonable and practical.
  • Even less information is available regarding MRSP, mostly because it's not considered a major human health issue. That being said, you don't want to get a multidrug-resistant bacterial infection, even if it's uncommon. Therefore measures to reduce the risk of transmission of MRSP from pets to people is should still be considered.
  • Strict isolation of infected pets is probably excessive. General infection control practices (e.g. handwashing after contact with the animal, avoiding contact with the infected site, limiting contact overall) are probably adequate, especially in households with no high-risk people (e.g. people with weakened immune systems, infants, elderly individuals).

More information on both MRSP and MRSA can be found on the Worms&Germs Resources page.

How long do animals carry MRSP/MRSI?

I've had this question a lot lately. Methicillin-resistant Staphylococcus pseudintermedius (MRSP), which is sometimes misidentified as methicillin-resistant S. intermedius (MRSI), is an important and increasing cause of infections in dogs and cats. After an animal has had an MRSP/MRSI infection, a question people often ask is how long they will carry the bacterium?

MRSP can be carried in the nose, intestinal tract or on the skin of a small percentage of normal animals. The implications of this are not clear, but it is reasonable to assume that carriers are more likely to develop infections in certain situations (e.g. if they sustain a wound or need to have surgery), and can transmit it to other animals (and possibly people, but that's much less of a concern with MRSP than with MRSA).

Back to the question... To be perfectly honest, we really don't know. However, I think it's reasonable to assume that some animals could carry MRSP for a long period of time - certainly weeks or months, maybe even years. Staphylococcu pseudintermedius is a common bacterium in healthy dogs and cats, and has basically evolved to survive on these animals. The methicillin-resistant versions are likely no different in this respect, so it's reasonable to assume that some animals could be long-term carriers. This makes controlling MRSP more difficult.  In contrast, MRSA appears to be only transiently carried by dogs and cats, probably because it is better adapted to living on humans than pets.

What you should do in the meantime if your pet has MRSP:

  • Treat any infection as per your vet's instructions.
  • Always complete the full treatment course.
  • Wash your hands after contact with your pet, healthy or not.

More information about different types of staph bacteria can be found in the previous Worms&Germs post entitled Methicillin-Resistant Staph - What's In A Name?

Healing with honey

As we encounter more infections caused by antibiotic-resistant bacteria (e.g. MRSA), we need to explore treatment options other than antibiotics. While we usually focus on "new" treatments, sometimes we can look back in time for ideas to treat infections. An old treatment method that is getting increasing attention these days is the use of honey. Honey may be a safe, effective and affordable treatment option in many cases. Click on the picture below to view a video by Dr. Karol Mathews, a critical care specialist at the Ontario Veterinary College.

MRSA in veterinary surgeons study: results

An MRSA prevalence study was recently performed at the American College of Veterinary Surgeons (ACVS) conference in San Diego, CA. As per the study protocols, results are being made available through  the Worms&Germs website. Click here to download the results file. This file contains code numbers for all positive results. If your number is not there, we did not isolate MRSA from your swab.

If MRSA was isolated from your swab, please do not panic! MRSA can normally be found in a small percentage of healthy individuals. Rates of MRSA carriage are higher in some groups, such as veterinarians. Most people that are carrying MRSA do not have any problems. In most situations, people in the general population that are carrying MRSA are not treated to eliminate colonization. However, if you are concerned about your result, we recommend that you contact your physician.

We appreciate your participation in this study. Analysis of the results is ongoing to look for factors associated with MRSA colonization. Further testing of MRSA isolates to characterize them is also ongoing.  If there are any problems or questions, please contact Scott Weese at


Chloramphenicol: the good, the bad, and the "beware"

As we see more and more infections caused by antibiotic-resistant bacteria, we have to re-think our approach towards antibiotic therapy. This often involves using new drugs, but sometimes it also involves considering the use of older drugs that we haven't used very much for a long time.

One such drug is chloramphenicol. Years ago, this antibiotic was widely used, and is still used in people and animals in some situations. In some respects, it is a very good antibiotic - it is often effect against many bacteria including those that are resistant to many other drugs, such as MRSA and MRSI/MRSP.  Chloramphenicol can also be given orally, and it's relatively cheap. Unfortunately this drug can also be very toxic, both to the animals being treated with it and to people that come in contact with with it in the process. In some animals, chloramphenicol can cause suppression of the bone marrow, where red and white blood cells are produced. This is more of a concern with long term use, but if the bone marrow does become suppressed, stopping treatment with the chloramphenicol typically resolves the problem.  Unfortunately, this bone marrow suppression is much more of a concern in people - the supression is very severe, and can occur with exposure to even a very low dose (or probably single dose) of chloramphenicol.  This results in a condition known as aplastic anemia,  which it typically fatal.  Fortunately this reaction is very rare in people, but there is no way to predict who might develop this condition, and since it is usually fatal, we obviously need to be cautious about using this drug. In some countries, chloramphenicol use in banned in all animals. In many others, it cannot be used in food animals, but can be used in pets.

  • Chloramphenicol should only be used as a drug of last resort. There are situations where it is useful and may be life-saving, but the human health risks cannot be overlooked.
  • If chloramphenicol is being considered, it is critical that  people who would need to handle the drug understand the risk and how to safely handle the drug to avoid exposure.
  • Chloramphenicol tablets should not be crushed or otherwise processed at home because of the potential for breathing in the drug when it is in powder form.

Direct contact with pills or liquids should be avoided by use of gloves or other safe handling practices.

  • If a liquid form is used and is squirted onto food, the food bowl should be handled as if it is contaminated.
  • If pills are being used, the animal should be observed to ensure that the pill is ingested and not spit up and left on the floor.
  • Contact with the mouth and face and animals that are being treated with chloramphenicol should be avoided in case drug residues are present.

If people are unable or unwilling to follow safe handling recommendations, they should not use this drug.

Your mother was right! Wash your hands

You may notice a recurring theme in many of our posts and on virtually all of the information sheets on the Worms & Germs Resources page: an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.

Most of the research about hand hygiene that has been published has focused on its use and impact in human hospitals, but this area is now also being studied more with regard to animals and veterinary medicine. A study published earlier this year in Veterinary Microbiology provided more evidence that hand hygiene is a critical infection control measure when dealing with animals. The study, coordinated by Dr. Maureen Anderson (of Worms&Germs fame) looked at MRSA carriage rate in veterinarians who work with horses. In addition to finding a high rate of MRSA carriage among these veterinarians (which was consistent with other reports indicating that equine vets are at higher than average risk for exposure to MRSA), the study looked at factors associated with MRSA carriage. Vets that reported routinely washing their hands between farms and those that reported washing their hands after contact with potentially infectious cases had a significantly lower rate of MRSA carriage. That should come as absolutely no surprise, but it's one more piece of evidence that we need to pay more attention to this routine infection control measure, in human hospitals, in veterinary environments and in households.

Remember, the 10 most important sources of infection are the fingers on your hands!

Click here for instructions on how to wash your hands properly.

What puts dogs at risk for MRSA?

It's clear that methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a problem in dogs, both in terms of dog health and in terms of dogs as a potential sources of infection for people. It is thought that MRSA in pets is often (if not usually) acquired from people. Until recently, it has been unclear what makes individual dogs more likely to infected by MRSA compared to other bacteria. A study by Dr. Meredith Faires from the University of Guelph has provided some important new information in this regard. The study compared dogs with MRSA infections to dogs with infections caused by methicillin-susceptible strains of S. aureus (also called MSSA), from three large veterinary hospitals. Here are some key findings from Dr. Faires study:

  • Animals that received fluoroquinolones were significantly more likely to develop an MRSA versus an MSSA infection.  Fluoroquinolones are a specific class of antibiotics that includes drugs such as enrofloxacin, orbifloxacin and marbofloxacin.
  • In both groups (MRSA and MSSA), most of the infections were skin and ear infections, with no significant difference in types of infection between the groups.
  • There was no difference in the proportion of animals that survived their infections between the two groups: in both groups, over 90% of the animals survived. However, it is important to bear in mind that the majority of the infections were skin and ear infections, which are not usually life-threatening.  Further study of more serious types of infection is needed to determine if MRSA is associated with a greater risk of death in dogs and cats.

This study provided more evidence that MRSA is an important problem in dogs and cats, and that the use of antibiotics is likely an important factor in the development of MRSA infections, compared to infections caused by MSSA. It also showed that the survival rate for common types of MRSA infections is high, if the infection is properly diagnosed and managed.  Hopefully the information provided by this study can be used in future studies to help evaluate more risk factors, and to identify things that can be done to reduce the impact of MRSA in dogs and cats.

More information about MRSA in pets can be found on the new MRSA information sheets posted on the Worms & Germs Resources page.

Picture: Gram stain of Staphylococcus aureus


If you are looking for an interesting website to play around with, you should try HealthMap. This is a website created by the Harvard-MIT Division of Health Sciences and Technology that maps infectious disease reports from various sources. You can search by region and see what disease problems have been reported recently, or select specific diseases and find out where they've been reported.   Some examples are shown below. The top image shows all disease reports worldwide (in the last 30 days), while the bottom image shows reports of Salmonella in North America during the same time period. The site relies on reports of diseases (many cases of various diseases occur but are never reported), so it focuses mainly on outbreaks or high profile cases , but it is still quite interesting.

Above: All reported disease outbreaks/cases worldwide in the last 30 days.
Below: Reported outbreaks/cases of Salmonella in North America in the last 30 days.
See the HealthMap site for more details.

Treatment of MRSA and MRSP: more than meets the eye

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant S. pseudintermedius (MRSP) are important causes of infection in pets, and are resistant to many different antibiotics. It's therefore very important that these bacteria are cultured and tested in a lab to determine what antibiotics may be effective.  Even then, choosing an effective medication can be difficult due to the limited number of potentially effective drugs.

Treatment selection is further complicated by problems that can occur when methicillin-resistant staphylococci are tested against certain drugs in the lab - problems that are not readily apparent unless extra testing is done.  One "problem" drug is the antibiotic clindamycin. Clindamycin can be an effective treatment for MRSA or MRSP infections, but some MRSA strains may be resistant to it despite appearing to be susceptible based on normal laboratory testing. This is because the bacteria can have "inducible resistance".  Inducible resistance can be detected by a special test called a D-test (see picture), but this test is not widely performed in veterinary laboratories.

In recent study presented by Dr. Meredith Faires (University of Guelph) at a conference last week, 55% of MRSA from dogs and cats that were reported to be resistant to erythromycin and susceptible to clindamycin were actually inducibly resistant to clindamycin.  But no MRSA that were susceptible to erythromycin were inducibly resistant to clindamycin. In contrast, inducible resistance to clindamycin was not identified in any MRSP. Therefore, in the absence of specific testing for inducible resistance (i.e. a D-test), it is wise to consider all erythromycin resistant MRSA to be clindamycin resistant as well, regardless of the results of traditional antibiotic susceptibilty testing.

How did dogs get MRSA?

A common question from owners of pets infected with methicillin-resistant Staphylococcus aureus (MRSA) is "Where did it come from?" The answer is not completely clear, but evidence strongly suggests it probably came from humans. The MRSA strains found in pets are almost always teh same as those found in people (including people that don't have pets) in the same geographic area. This strongly suggests that the MRSA came from the same source. Considering the fact that S. aureus in general is much more common in humans than in pets, and how long MRSA has been around in people, and that MRSA can sometimes be found in both people and pets in the same household, it is very likely that MRSA can move between species and originally went from humans to animal.

Even though MRSA in pets probably originated from people, now that it is in the pet population, pets can spread it to other animals and back to people. It is unclear how frequently this occurs - most people are still more likely to encounter MRSA from another person than from an animal.

The emergence and spread of MRSA in humans was largely driven by extensive antibiotic use in people.  Once MRSA crossed over to pets, antibiotic use in these animals almost certainly played a role in helping MRSA spread in the pet population. Antibiotic treatment has been identified as a risk factor for development of MRSA infection in dogs, and for MRSA carriage in horses.

Prudent antibiotic use is likely the most important factor in reducing the risk of MRSA in individual pets.  Using antibiotics prudently means doing things like:
  • Only using antibiotics when they're really necessary
  • Using the most basic antibiotic possible (instead of the fanciest or most powerful antibiotic)
  • Finishing every prescription completely and as directed)

Hot spots

This time of year, hot spots (aka superficial pyoderma, moist pyoderma, pyotraumatic dermatitis) are a common problem in dogs. Hot spots are more common in males, and most often occur on the cheek (pictured), neck or outside of the thigh. Normal skin is covered with various bacteria but infections don't develop because healthy, intact skin is a natural protective barrier. Hot spots typically occur when the skin's normal barrier is compromised from scratching (e.g. from allergic skin disease, insect bites) or chronic moisture (e.g. under the ear or collar of dogs that swim a lot). Hot spots are typically red, with oozing serum or pus on the surface and a foul smell. They are often itchy, so affected dogs with repeatedly scratch the area, but they may also be very painful.

Various bacteria can cause hot spots. Most commonly, Staphylococcus pseudintermedius is involved. Hot spots are quite low risk for transmission to other animals or to people, although it is possible for concerning bacteria like methicillin-resistant S. aureus (MRSA) to be involved. Only a culture of the infected site can determine the bacterium that is involved.
  • Most hot spots are easily treated. This typically involves clipping the hair around the infected site and scrubbing the area with antibacterial soap. Sometimes, antibiotics and/or anti-inflammatories are also needed. The infected site should be kept as clean and dry as possible.
  • While most hot spots are not caused by bacteria that are a major concern for transmission to people or their animals, any infected site should be handled with care. Direct contact with the hot spot should be avoided.
    • If the infected site needs to be touched, gloves should be used if possible, and hands should always be thoroughly washed after touching the site.
    • Care should be taken when touching hot spots because they can be very painful, and touching them could make some dogs bite.
  • Prompt examination by your veterinarian will help ensure your pet gets the treatment it needs as soon as possible, and ultimately helps speed recovery.
  • Always follow your veterinarian's recommendations closely and completely. Stopping treatment too early can lead to recurrence of the infection, which may be more difficult to treat.
Image from

Is it a spider bite or MRSA?

Skin reactions from spider bites are usually very mild, if they are even noticed.  However, bites from certain kinds of spiders can cause severe skin lesions that may develop into  deep open wounds.  These are sometimes called "volcano lesions". Deaths due to such bites have been reported, mainly in children. However, the relatively small brown recluse spiderLoxosceles reclusa (see picture), is the only one of approximately 20 000 different species of spiders in the Americas that can cause these severe lesions. This spider is native to the midwestern and southeastern US, and is rarely found elsewhere.

In many cases (particularly in people but also in pets), a variety of focal skin lesions, including volcano lesions, may be diagnosed as a "spider bite" without any further testing. This is even done in areas where  brown recluse spiders don't live!  Another possible cause of a volcano lesion that may be mistaken for a spider bite is methicillin-resistant Staphylococcus aureus (MRSA). It is clear that many MRSA infections in people are being misdiagnosed as spider bites, but I have also talked to various pet owners whose dogs had MRSA infections that were originally diagnosed as spider bites. Most of these were from areas where brown recluse spiders would never be found. If an MRSA infection is diagnosed initially as a spider bite, the delay in starting proper treatment can lead to more prolonged and potentially more serious disease.

In addition to MRSA, the related bacterium methicillin-resistant S. pseudintermedius (MRSP), which is more common in dogs and cats than in humans, could be involved in similar skin infections. This is just as serious for the pet, but less of a concern for people in contact with the pet.  For more information about MRSA versus MRSP, check out our blog on Methicillin-Resistant Staph: What's in a Name?
  • MRSA, MRSP and other infectious agents should be considered as potential causes for focal skin lesions, particularly if they form deep open wounds or an abscess containing pus.
  • Volcano lesions should not be assumed to be spider bites unless a bite from a brown recluse spider was observed.  Such lesions should definitely not be diagnosed as spider bites in regions where the brown recluse spider does not live.
  • Wash your hands if you touch any unusual skin lesion on a person or a pet.

EU Antibiotic Awareness Day

The European Union has announced that November 18 will be the EU's Antibiotic Awareness Day. Antibiotics are incredibly important drugs and save countless lives (human and animal) on a daily basis. Resistance to antibiotics is a major threat to human and veterinary medicine. While antibiotic resistance is a complex issue, overuse and improper use (in animals and people) undoubtedly contribute to the emergence and spread of resistant bacteria like MRSA. Awareness of these concerns is important for healthcare professionals (both human physicians and vets) and the general public. Here are some general points to remember with respect to pets and antibiotics:
  • Do not encourage your vet to prescribe antibiotics when they are not necessary. Vets (and physicians) often feel pressure to prescribe 'something', even though they have no clear evidence of a bacterial infection. Antibiotics do not work for viral infections.
  • Never give antibiotics to your pet without the direction of your vet.
  • Always give the full antibiotic course, as prescribed. Do not stop early. Your pet may look better but the infection could still be there.
  • Never save antibiotics for 'future use'. If your pet develops another infection, you need to have your pet evaluated by a vet to determine if antibiotics are needed, and what antibiotic would be best.

Methicillin-resistant staph: what's in a name?

There is a lot of concern and confusion about methicillin-resistant staphylococcal infections in pets. "Staphylococcus" is genus of bacteria which contains numerous different species. All these species can come in 'methicillin-resistant' forms that are resistant to many antibiotics, but some of these species are of greater concern than others. The main species of concern are discussed below.

Methicillin-resistant S. aureus (MRSA): This species is the big concern. MRSA is an important cause of disease in people and an increasing problem in pets. It can cause serious infections and be transmitted between animals and people (in both directions).

Methicillin-resistant S. intermedius (MRSI): Actually, what most laboratories still call S. intermedius appears to be a related species called S.  pseudintermedius. Regardless, MRSI (or MRSP) can cause a variety of infections in pets - usually skin and ear infections. While it can be spread from animals to people, this is likely rare and there is much less concern about MRSI compared to MRSA in terms of risk to humans from infected pets.

Methicillin-resistant S. schleiferi (MRSS): This species is closely related to (and often misidentified) as S. intermedius. It is most commonly found in skin and ear infections. There is no information about the risk of transmission to people from pets. It is probably possible but very unlikely.

Methicillin-resistant coagulase-negative staphylococci: This is a large group of staphylococcal species that are usually lumped together. They are commonly found in or on healthy dogs and cats as part of the body's normal bacterial population. They are less common causes of disease. There is currently minimal concern about transmission to humans.

MRSA is the main concern with regard to staph infections, and warrants particular attention when it causes infection in a pet. In these cases, important precautions to take include washing your hands frequently, avoiding contact with the infected part of the animal's body (plus the nose, where MRSA often hangs out), keeping the infected site(s) bandaged (if possible), keeping infected pets off the bed, and restricting contact with high risk people (e.g. young children, elderly, immunocompromised). For the other staph species, the risks to people are much lower, but it is still reasonable to implement these measures to further reduce the risks.

I've been diagnosed with MRSA....could my pet be the source?

Methicillin-resistant Staphylococcus aureus (MRSA) is a multidrug resistant bacterium that is often referred to as a 'superbug'. It is an important cause of disease in people, both in hospitals and in the general population. It can also infect various animal species, including dogs and cats. A small percentage of healthy people and animals (1-3%) carry MRSA without knowing it, and usually without ever having any problems. Unfortunately, increasing awareness of the potential for healthy pets to carry MRSA has led to excessive focus on pets in some situations. While transmission of MRSA between people and pets can happen, it is probably more common for it to go from people to pets, than pets to people. Pets should not be 'blamed' for human MRSA infections without good evidence, and there are only certain situations where evaluating pets is currently indicated.

Here are some important points from the Canadian guidelines for management of community-associated MRSA in people.
  • Testing of pets for MRSA carriage should only be considered when there is recurrent MRSA in the household and transmission is ongoing despite the implementation of household infection control measures.
  • Testing of pets should only be done as part of an overall investigation of the household. Testing of pets but not human household contacts is not indicated.
  • Removal of the pet should only be considered in exceptional circumstances, and removal should be temporary. Such circumstances could include households where controlling contact with the pet is not possible and/or when people in the household are being treated to eliminate MRSA carriage. The beneficial effects of pet contact should be considered in any discussion about removal of the pet from the household.
If you have MRSA, wash your hands frequently, limit contact with your pet's face and do not touch wounds on your pet. These should greatly reduce the risk of MRSA transmission.

Horses and MRSA

Many people in the horse world have heard the hype about methicillin-resistant Staphylococcus aureus (MRSA) in horses. MRSA can cause infection in horses, just like it can in people, dogs, cats and many other animals. It’s usually what we call an “opportunistic” pathogen, meaning it usually takes advantage of a person or an animal that is already sick or injured, like someone who’s in the hospital and has just had surgery. And because MRSA is resistant to many different antibiotics, the infection can be difficult to treat. The big concern with MRSA in recent years is that infections are now sometimes occurring in people who aren’t sick, and who don’t have wounds or incisions, which is where MRSA usually likes to move in. It’s very important to find out from the start if an infection is being caused by MRSA, so that it can be prevented from spreading to other people and animals, and so that it can (if necessary) be treated with the right kind of antibiotic.

Horses are a bit of a special case when it comes to animals and MRSA. When researchers look at the DNA of MRSA from a dog or a cat, it usually turns out to be one of the common human MRSA strains (usually called a “clone”) from the same area. This means that the dog or cat probably picked up the MRSA from a person somewhere.  When researchers look at the DNA of MRSA from horses, however, they often find a different clone, which seems to be more common in horses and people who work with horses than in people in general. A very similar situation has also been discovered in pigs. The worry is that this “horse MRSA clone” can survive in and be transmitted between horses better than the human MRSA clones. That means that in order to control MRSA, just controlling it in the people won't do the trick - we need to take steps to stop the spread of MRSA in horses specifically as well.

Here are some key points to help reduce the risk of your horse (and you!) getting MRSA

  • Always wash your hands with soap and water (or use an alcohol-based hand sanitizer) after handling a horse, and before handling another horse.
    • This is especially important if you have touched a horse’s nose, or any cuts or wounds that the horse may have.
    • Don’t go down the row of stalls in the barn and pet every horse on the nose! They love the attention, but this is a great way to spread MRSA if it’s there!
  • New horses coming into the barn, or animals coming back from a hospital, should be kept separate from all the other animals and only dealt with after all the other horses, for 3-4 weeks.
    • This is an important measure for controlling many infectious diseases, not just MRSA.
  • If your horse has a cut that looks infected, cover it with a bandage of some kind and contact your veterinarian. Your veterinarian can culture the wound to determine if it is an MRSA infection.

My dog has MRSA... what do I do?

This is a question that I get on a regular basis. Methicillin-resistant Staphylococcus aureus (MRSA) is an antibiotic resistant bacterium that is a major cause of disease in people and is also a cause of disease in various animals species, including dogs and cats. It can cause a wide range of infections, from mild skin infections to rapidly fatal disease. Most MRSA infections in animals are treatable if managed properly and most are treated in the home (as opposed to requiring a stay at a vet clinic). Because of this, there are concerns about transmission of MRSA from infected pets to people in the household. Transmission of MRSA between people and pets (in both directions) definitely happens, although we don't really know how often this occurs.

If your pet has MRSA:
  • Talk to your veterinarian about how to handle the infection
  • Avoid contact with the infected site. If you have to touch it, use gloves and wash your hands         immediately afterwards.
  • Wash your hands regularly after contact with your pet
  • Avoid contact with your pet's face...MRSA often lives in the nose, in addition to the site of infection
  • Try to limit overall contact with your pet until the infection has resolved. Close, prolonged contact such as letting the pet sit on your lap or sleep on your bed should be avoided
  • Follow your veterinarian's instructions closely. Always complete the full course of treatment, even if your pet looks better
  • Talk to your physician if you have concerns about your health, particularly if you or someone in the household has a compromised immune system
Should I be tested?
Current recommendations are that there is no indication to test people or pets for MRSA carriage when there is an infected pet (or person) in the household. Testing might be reasonable in some circumstances where uncontrolled transmission of MRSA appears to be occurring in a household, but there does not seem to  be a reason to test with single incidents of MRSA infection.

Studies are currently underway looking at transmission of MRSA in households where pets have an MRSA infection. Better information will likely be available in the future as a result of these studies.

More information on MRSA in pets will be available soon in our Resources section.  Another good source of information is the Bella Moss Foundation, a charitable foundation dedicated to MRSA in animals.

Horse visits hospital

Recently, a story about a man who brought a horse into a hospital to visit his father was widely reported. The horse apparently made it to the man’s room, which included a trip in an elevator. The son, who appeared intoxicated, was eventually asked to leave (and take the horse with him). Said a hospital spokesperson “We do have a pet visitation policy, but it does not include a horse”. Strangely, the horse that was brought to the hospital apparently wasn’t even the father’s horse (which supports suspicions of the son’s lack of sobriety).

There are guidelines about which animals are appropriate for hospital visits, although it shouldn’t take an expert to figure out that a horse is not an appropriate candidate. Kicks, bites, and trauma from being crushed or run over are among the most obvious concerns. Horses can also carry a variety of bacteria that are potentially dangerous, especially to people in hospitals. These include Salmonella and methicillin-resistant Staphylococcus aureus (MRSA). There also aren’t that many house-trained horses out there.

So, while I can easily see how someone in a hospital would like to see his or her horse, there’s no way this should even be considered.

Some closing thoughts
-    Would you like to ride in an elevator with a horse?
-    Would you like to be stuck in an elevator with a horse?
-    Do you think the horse was house trained?
-    Do you think any of the healthcare personnel washed their hands after touching the horse?

This isn't the first time a horse has been in hospital, and some even get invited. The picture is from a story in Veterinary Practice News that described a program where horses were brought into hospitals!

UK Chief Vet says no pets in bed

The UK’s Chief Veterinary Officer Fred Landeg recently declared that pets should not be allowed to sleep in peoples’ beds or even be allowed in the bedroom.  The reasoning behind this recommendation was the potential for transmission of bacteria such as Salmonella and Campylobacter. This was in response to a publication in the Veterinary Record describing animal-human interactions in households in the UK. It reported that 20% of participants let their dogs sleep in the bedroom and 14% let their dogs sleep in their bed.

While it is certainly true that any healthy animal (and person) can carry infectious diseases, and that prudence is reasonable, there is simply no evidence supporting this recommendation for the average household. Any contact with pets carries a very slight risk of disease transmission, just like any contact between people. There is currently no evidence, however, that sleeping with a pet in the bed increases the risk of disease. For your average pet and average household, this is probably exceedingly low risk and the recommendation is very difficult to justify. It is a reasonable recommendation when the pet is known to be carrying something that is transmissible to people (such as MRSA or Salmonella) or when a person has a compromised immune system. Banning pets from the bedroom completely doesn’t make any sense.

Personally, my dog is not allowed in my bed. However, that’s not because of disease concerns, it’s because she’s a large dog that snores and certainly can be a bed-hog. I have no problems with my cat on the bed. Life is never completely free of risk. If you enjoy having your pet in the bed, and you’re both healthy, I don’t see a reason to stop.

Are cats the root of all evil?

A Letter was just published in the New England Journal of Medicine about a woman with recurrent methicillin-resistant Staphylococcus aureus (MRSA) infections and her cat. MRSA is a hot topic because it’s a big cause of disease in people and there are indications that it can be transmitted between people and pets (in both directions). She kept getting recurrent infections and they eventually cultured MRSA from her cat. The cat was not sick and was a carrier. That’s something that we’re seeing increasingly, although we don’t know whether the pets are actually involved in transmission or whether they are innocent bystanders that are infected by their owners. The concerns that I had with this Letter revolve around the fact that the cat was treated for MRSA (in my experience, carriage of MRSA by dogs and cats is transient and antibiotics aren’t needed), they never tested the cat after treatment but they declare that the woman’s infections only ceased after the cat was treated. The problem is, the cat may have gotten rid of MRSA despite the antibiotic treatment, the owner may have handled the cat differently after finding out it was MRSA positive and therefore decreased the risk of transmission, or it may never have played a role in her infections.

Unfortunately, this Letter may lead to unnecessary treatment of pets that carry MRSA or over-assumption of the role of pets in human infections. It also meant that I was stuck doing rounds and rounds of interviews with reporters wanting comments. The key take-home messages from this are:

- Pets are part of the household and should be considered if a household disease investigation is undertaken.
- While pets may sometimes be involved in transmission of MRSA, simply finding MRSA in a pet does not mean that it has infected anyone.
- There is currently no indication that we should be using antibiotics to get rid of MRSA colonization in pets because they almost invariably get rid of it on their own.

Information Sheets for Pet Owners

INFORMATION SHEETS specifically for KIDS, for VETERINARIANS, for PHYSICIANS and for PUBLIC HEALTH PERSONNEL are also available on the Worms & Germs RESOURCES page!

Click on the highlighted topics below for information sheets. Topics that are not highlighted are in development and coming soon. Sheets for other animal species and diseases are also under development and will be added when they are available.

Diseases Other
Dogs Rabies Litter Boxes
Cats Giardia Sandboxes
Turtles Toxoplasma Cat Bites
Hamsters Leptospira Raw Meat
Rabbits Clostridium difficile Petting Zoos
Pet Birds Cryptosporidium Needlestick Injuries
African Dwarf Frogs MRSA  
Reptiles MRSP  
  MRSP (Deutsch)  
  MRSP (Francais)  
  Rat Bite Fever  
  Cat Scratch Disease  
  Lyme Disease & Ticks  


Please Remember:

  • Your veterinarian and physician are your ultimate resource for information about the health of your pets or your family.
  • Information provided here is accurate to the best of our knowledge, but infectious diseases can be unpredictable and these sheets are for general information purposes only.
  • There can be great variation in disease risks in different geographic areas. The information provided was developed for Ontario, Canada, but most of the information is relevant for other regions as well.

Research Posters

2012 International Clostridium difficile Symposium

2012 International Conference on Equine Infectious Diseases IX

2011 ASM-ESCMID Conference on Methicillin-resistant staphylococci in animals

2011 University of Guelph Centre for Public Health and Zoonoses Symposium

2011 Canadian Animal Health Laboratorians Conference

2011 Canadian Association of Clinical Microbiology and Infectious Diseases

Coming soon

  • 2011 American College of Veterinary Internal Medicine Forum, June
  • 2011 ASM-ESCMID conference on methicillin-resistant staphylococci in animals, Sept