Worms & Germs Blog

Agritourism Infection Prevention

Posted in Other animals

Petting goatAgritourism is becoming a big industry. As our society gets more urbanized, there’s increasing interest in visiting farms and similar environments. Things like farm visits and petting zoos can be great, especially for kids. They’re also sometimes associated with infectious diseases, most often in kids.

Some agritourism events are well run and take a lot of measures to reduce the risk of disease transmission (and injury). Some… well… they aren’t living up to the increasing standards and expectations.

A few years ago, we did some studies looking at petting zoos and infection control practices. Various issues such as having high risk species (e.g. calves, young poultry), people eating in animal contact areas, limited handwashing facilities and lack of supervision were common (Weese et al. Clin Infect Dis 2007). A webcam- based observational study at one event showed that even with good design, handwashing rates amongst participants were relatively low (Anderson and Weese, Epidemiol Infect 2011).

I think things have improved a bit around here over the last few years, but it’s still not hard to find some pretty dodgy events. Further, it’s not hard to find reports of infectious diseases or outbreaks associated with events like these (for example, recent cases of E. coli infection associated with a county fair in Oregon). While these events can be rewarding, more needs to be done to reduce the risks associated with them.

An agritourism operator isn’t necessarily an infectious disease expert. As a result, information about how to reduce infectious disease risks is needed. Sometimes there’s just a basic “wash your hands” poster from the local public health unit. That’s a start, but is only part of the story. More comprehensive guidelines are becoming available to help facilities better design and operate their events, thus protecting the public and themselves (lawsuits are far from rare when it comes to farm-associated diseases, especially outbreaks).

The Upper Midwest Agricultural Safety and Health Center (UMASH) has launched a new website with some good information for agritourism operators and the general public. These types of resources should be mandatory reading for anyone operating an agritourism event.

Diagnostic Crotch Sniffing?

Posted in Dogs, Miscellaneous

Lab sittingDogs’ noses are used for a lot of things. Some are conventional (e.g. tracking, search and rescue, drug detection), some are a bit outside of the box (e.g. detection of Clostridium difficile, identifying floating whale poop). A recent paper in Open Forum Infectious Diseases (Maurer et al 2016) takes this to another level by investigating the use of dogs to detect bacteriuria – the presence of bacteria in a urine sample.

Five dogs (Labs and Golden retrievers) were trained to detect contaminated urine in scent detection boxes. When they came across a contaminated urine sample, they sat in front of the box. That’s a pretty standard training approach.

After the training phase, they took urine samples with fairly high levels of bacterial contamination and samples with no bacteria, and saw how good the dogs were at identifying the contaminated samples. They then tested urine samples that were diluted to 1% and 0.1% and did the same thing.

The results were pretty impressive:

  • For E. coli, the most common bug involved in urinary tract infections, the sensitivity of the “sniff test” was 99.6%. That means the dogs detected 99.6% of positive samples (and therefore had few false negatives, aka samples that were actually positive that they missed.) The specificity was 91.5%, so 8.5% of positives were false positives (aka negative samples that were mistakenly identified as positive). Overall, the results mean that if bacteria were present, the odds were very good that the dogs would detect it, with a relatively small percentage of additional positives being false alarms.
  • Results were similar with other bacteria.
  • Diluting samples to 1% or even 0.1% did not impact the sensitivity or specificity.

So, it seems that dogs can do a good job figuring out whether urine has bacteria in it.

Is having a dog that is able to detect bacteria in urine samples useful?

  • Probably not, at least in practical terms. I doubt someone’s going to keep a trained dog around to pre-screen urine samples.
  • Testing urine for bacteria only provides part of the needed information. The susceptibility of the bacterium to antibiotics is another key piece of information, something that even the best dog nose can’t sort out.

What if the dogs can detect bacteriuria directly in certain people, such as those with spinal cord injuries or other conditions that hide other signs of urinary tract infections?

  • That might be more interesting. However, asymptomatic bacteriuria (presence of bacteria in the absence of disease) is common in these same groups of patients and treatment is rarely needed, so it might not be a useful screening tool anyway. In fact, there’s a lot of effort being taken to reduce unnecessary cultures and unnecessary treatment of people with asymptomatic bacteriuria, so finding more of those individuals might be counterproductive.

How well would dogs do trying to detect bacteriuria directly in people?

  • That’s another good question.  I suspect there’d be a lot of other distracting smells when sniffing urine directly from a person or other animal.
  • However, an interesting anecdote is reported in the paper. One month after the study, one of the dogs alerted to a person at the training centre. That person wasn’t feeling well but didn’t suspect a urinary tract infection. However, based on the dog’s response, a urine culture was done and bacteria were present.

Regardless, it’s an interesting study and certainly not the last report of using dogs to detect a human health problem that we’ll see in the near future.

It also makes me wonder about owning or handling one of these dogs. It might be a bit awkward explaining to the person you meet walking down the street why your dog is sitting in front of them and staring at them. A little too much information perhaps.

In terms of my own dog, Merlin, well, he has a great nose and he’s great at the “staring at someone’s crotch” component that a dog like this would need. Unfortunately, the connection to his brain (what there is of that) is pretty weak. He’ll remain blissfully unemployed.

Guinea Worm in Dogs

Posted in Dogs

There are a lot of gross parasitic diseases. A prime example is dracunculiasis, otherwise known as Guinea worm (Dracunculus medinensis) infection. People get infected by drinking water or eating undercooked fish contaminated with “water fleas” that are infected with Guinea worm larvae. Over a year or so, the worm grows silently in the body, with females reaching 60-100 cm in length. Fertilized female worms work their way to the skin surface, usually in the lower leg, cause a small blister. There, they expel larvae into water, where they can then infect someone else. The adult worms continue to emerge over the course of a few weeks, a very painful and troubling process for the infected person (see life cycle diagram below).

Guinea worm PHIL8211The image (left) depicts the emergence of a female Guinea worm from the lower leg of a person.  Once the worm emerges from the wound, it can only be pulled out a few centimeters each day and wrapped around a small stick, or piece of gauze. Sometimes the worm can be pulled out completely within a few days, but the process often takes weeks.  (Image source: CDC Public Health Image Library #8211)

Significant efforts have been underway to eradicate Guinea worm, and they’ve made a lot of progress. Human cases had dropped dramatically, from millions to handfuls. In 2014, only 126 cases were identified (down from 3.5 million in 1986); cases were from Chad, Ethiopia, Mali and South Sudan. Guinea worm was thought to have one key property necessary for successful eradication of disease: a single definitive host species. It was believed that the parasite needed humans to complete its life cycle, so if the disease could be eradicated in people, the parasite would be eradicated completely.

Unfortunately, that doesn’t appear to be the case. Guinea worm is now being found in dogs. Guinea worm infections in dogs were first identified in Chad a couple years ago (Eberhard et alAm J Trop Med Hyg 2014), and the numbers seem to be increasing. 600 infected dogs have been identified in Chad so far this year, so canine cases have now surpassed human cases, and it’s logical to assume that this represents just a small fraction of the true number of infected dogs. This complicates matters greatly, since it’s now evident that eradicating Guinea worm not only requires elimination of the parasite in people, but also in dogs (and possibly other species). That’s challenging, since keeping infected dogs tied up and away from water sources (which they can contaminate with the parasite larvae) for a couple weeks as the worm makes its way out of the body isn’t easy to do. The Carter Foundation is actually paying people to do just that, which actually seems to be helping.dracunculiasis_lifecycle

Whether dogs are a source of Guinea worm outside of Chad, and how much they contribute to human infection needs to be studied. Methods to prevent and treat infections in dogs need to be investigated too. At best, this will complicate and delay eradication of Guinea worm. At worst, it will prevent eradication altogether. Efforts to reduce exposure of people through access to uncontaminated drinking water will still be effective, but the more infected individuals (canine or human), the more surface water contamination there is. Exposure to people via surface water is hard to completely eliminate, so if it remains in dogs, human infections will continue to occur.

This is just one more example of how parasites (like bacteria and viruses) often find ways to confound our thinking.

Why Do Zika and Other Mosquito-Borne Viruses Only Occur in Specific Areas?

Posted in Other animals

When I got into vet school, I didn’t imagine that I’d have to know much about mosquito biology. (I probably didn’t really imagine that when I graduated either, to tell the truth). However, as I focused on infectious diseases, it became apparent that understanding certain aspects of inner-workings of mosquitoes (and ticks, and various other annoying critters) was critical.

We have a lot of mosquitoes in Ontario (a few billion of which live in the “protected wetland” (aka swamp) part of our property). We also have people from Ontario traveling to Zika-affected areas. Infected people can bring Zika virus home, where they could be bitten by Ontario mosquitoes. Why are we not concerned about Zika transmission here? The same could be said about dengue, chikungunya and a multitude of other mosquito-borne viruses that we don’t see transmitted here.

For sustained transmission of a mosquito-borne virus, you basically need two things:

  • A “reservoir host”: a population of infected individuals that infect mosquitoes. For Zika, that’s people (and as far as we know). For West Nile virus, it’s a variety of bird species.
  • A “competent vector”: In this case, that’s a mosquito species that can be infected when it feeds on a reservoir host, and then pass the virus on to the next person (or animal) it bites.

As people with travel-associated infections come home, there are/will be people in the province with the virus circulating in their bloodstreams, just waiting for a competent mosquito vector to which they can pass it along (or a sexual partner, but that’s another story). While rare, we do have the “host” component here.

The vector component is our saving grace here, at least at the moment. While all mosquitoes may seem the same to us – buzzing, biting, annoying – there are many different mosquito species. Zika is mainly spread by Aedes aegypti, a mosquito species that doesn’t live this far north. Another species, Aedes albopictus, is also a potential vector, and it has a broader range. The map below is from CDC, and while it looks like A. albopictus is either here or knocking on the door, it’s very rarely identified in Ontario, so the risk of it causing Zika problems (for now, at least) is very low.

Mosquito map

The reason I said “for now, at least” is that vector ranges are changing over time, probably due to climate change. While it will presumably be a long time before A. aegypti makes it this far north, it probably won’t take A. albopictus as long. So, over time, the risk might increase, especially if Zika establishes itself in the US.

The other question that often comes up when dealing with vector-borne diseases is the fact that we say “no known competent vectors.” That means that we don’t know of any insects in a region are definitely able to transit the pathogen. Does that really mean that none can? While the risk is probably low, there’s always some concern that there may be competent vectors that we don’t know about (or don’t realize are competent) just waiting to be infected. In Ontario, some ongoing work is testing Ontario mosquito species to see if any can be infected with Zika virus. They probably can’t, but it would be nice to know for sure.

Fatal Horse-Associated Streptococcus zooepidemicus Infection

Posted in Horses

Two horses in fieldA recent report in MMWR describes a pair of Streptococcus equi subsp. zooepidemicus infections in people.  The cases are noteworthy because this bacterium doesn’t often cause human infections, and because one of the infected people died.

More commonly referred to simply as Strep zoo, this bacterium is very commonly found in perfectly healthy horses, although it can cause a variety of infections in this species as well. It can also be found in some other animal species. In dogs, we see it periodically as a cause of pneumonia, which tends to be very severe and often fatal. The same applies in cats.  However, it can also be found in healthy dogs and cats, so it’s usually thought of as an opportunist, i.e. a bug that causes disease in unusual situations and secondary to some other inciting cause such as a viral infection or trauma. Human infections also occur, but they are uncommon and usually aren’t severe.

The two cases in the MMWR report were from Washington state. The first individual was an otherwise healthy woman who operated a riding stable. She developed mild cough and pharyngitis (sore throat), and at the same time, a horse she was taking care of developed eye and nasal discharge, and lethargy. The horse received antibiotics, and both horse and caretaker recovered uneventfully.

The second individual was the mother of the first patient. She visited her daughter and stayed at her house during the time that the daughter and her horse were sick, and she had direct contact with the sick horse on at least two days. The mother soon developed signs of an upper respiratory tract infection. About a week later, she started vomiting and had diarrhea, and was found unconscious the next day. She died the following day.

Strep zoo was not surprisingly cultured from a nasal swab of the sick horse. Also unsurprisingly, it was isolated from two healthy horses on the farm. Strep zoo was also isolated from a throat swab of the first woman and blood samples from her mother. When these bacteria were tested, the isolates from the first horse, one healthy horse and the two people were all an identical strain of Strep zoo. (The isolate from the other healthy horse was a different strain).

  • Finding Strep zoo in the horses, sick and healthy, is unsurprising.
  • Finding Strep zoo as a cause of mild disease in someone caring for an infected horses is not particularly surprising, although we don’t recognize it very often.
  • Fatal infection is surprising, although the age of the woman probably contributed to the severity. Whether she was infected from the horse or her daughter is unknown, but ultimately this was an equine-associated infection.

What came up with this case, and with similar mild cases in the past, was the question of “what to do” with the farm and with sick horses in general. There are no clear recommendations. Rarely do people take any precautions when handling horses that have (or might have) Strep zoo infections. You can see why, because human infections are so rare despite the fact that exposure of horse personnel to the bacterium is presumably very common.

But, what level of precaution is indicated?

Do we need to rethink what we usually do?

Does that change with people that are at increased risk because of age or immunocompromise?

  • It probably should.

How far to go in order to prevent what is probably a very rare outcome is hard to define.

The article takes a pretty balanced and practical approach, saying “Consistently practicing thorough hand washing with soap and water after contact with horses and other animals or areas where animals are housed is recommended. This outbreak highlights the need for more research regarding risk factors for zoonotic transmission and spectrum of human illness associated with S. zooepidemicus.”

That’s probably all we can say with much confidence.

Raccoon Roundworm Infection

Posted in Other animals, Parasites

Backyard raccoonThe August edition of Emerging Infectious Diseases has an interesting case report of Baylisascaris procyonis infection in a California man (Langelier et al. 2016). Baylisascaris procyonis, commonly known as the raccoon roundworm, is a parasite that is very commonly found in the intestinal tracts of raccoons. Massive numbers of parasite eggs can be found in areas where raccoons congregate to defecate (raccoon latrines). When a person ingests these eggs and they hatch, the parasite larvae can migrate throughout the body, particularly the brain, and cause significant damage.

This report details infection of a previously healthy 63-year-old man. His course of disease included 2 weeks of progressive fatigue and neurological abnormalities (e.g. confusion, headache, trouble moving his arm and head). He was hospitalized and continued to deteriorate. A sample of CSF (the fluid that surrounds the spinal cord and brain) had a few abnormalities, including an increase in eosinophils, a cell type that is often found in allergic and parasitic diseases. This led the physicians to consider an additional range of possible causes, and to ask some important questions. This questioning led them to discover that, among other things, the patient had recently undertaken a project under his house, where raccoons had been observed. As a result, they considered the potential for B. procyonis and started treatment while awaiting test results. Results were ultimately positive for the parasite.

A few noteworthy points:

  • It’s impressive that they considered B. procyonis. It took until eosinophilia was identified in the CSF to ask the critical questions about exposure, but at least they were asked fairly early in the process. This is a rare infection that wouldn’t normally jump to mind. A good history that included potential direct and indirect animal contact was the key. If they hadn’t gotten information about potential exposure to raccoon feces, they probably wouldn’t have tested. A good history goes a long way, but history-taking sometimes seems like a lost art.
  • Disease from this parasite in an otherwise healthy adult is very rare. Most of the small number of infections of which I am aware have been in young kids or kids with behavioural issues that made them higher risk for ingesting strange things like raccoon feces. Inadvertent exposure of a relatively healthy adult is unusual.
  • The patient responded reasonably well to treatment, particularly when compared to the usual (devastating) outcome. Whether this was because he was an adult, the infective dose was low, treatment was started early or he was lucky is unknown. It’s encouraging though, and another reason that getting a good history early in disease is so important. Early diagnosis (or even early consideration of infection) can lead to early treatment and better outcome.

Eastern Equine Encephalitis Season in Full Swing

Posted in Horses, Other diseases, Vaccination

‘Tis the season for mosquitoes, so ‘tis the season for some nasty vector-borne diseases. Few are worse that Eastern Equine Encephalitis (EEE), a viral infection that causes typically fatal disease in horses, and less commonly other species, including people. Cases tend to start mid-summer and peak late summer to fall, depending on the mosquito dynamics in the particular area.

This series of maps from WormsAndGermsMap (below) shows the progression of this disease in horses along the east coast of the US so far this year. Note that some flags represent multiple cases that occurred in the same area, so just counting flags doesn’t tell you the whole story.

I haven’t seen any reports of EEE in Canada in 2016 – yet. It’s a rare disease here but we often see a handful of equine cases each year.

Prevention

For horses, there is an effective vaccine. Vaccination is recommended in horses that live in (or travel to) typically affected areas. In areas where occurrence of EEE is rare but still plausible, it’s a good insurance policy, considering the safety of the vaccine and serious nature of disease, but it’s not considered a “core” vaccine.

The other important part of prevention is mosquito avoidance. That’s easier said than done, to some degree, but there are a number of things that can be done to reduce mosquito exposure, thereby reducing the risk of EEE as well as other mosquito-borne diseases (e.g. West Nile).

For people, the key is mosquito avoidance. A human vaccine is not available.

We haven’t heard the last of EEE this season, and we probably haven’t even neared the peak, unfortunately. The map is updated as cases come in so check WormsAndGermsMap for updates at any time.

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Move Over mcr-1. You’re Old News.

Posted in Other animals, Other diseases

Recent identification of mcr-1, a gene that makes bacteria resistant to colistin (an antibiotic of last resort) raised a lot of concern. Now, there’s another one to be worried about, as a related gene, mcr-2 has been identified (Xavier et al, Eurosurveillance, July 2016).

In this study, 105 colistin-resistant E. coli from calves and piglets in Belgium were studied. mcr-1 was found in 12% of these. They then looked at 10 of the bacterial isolates that were colistin-resistant but negative for mcr-1. They found a new resistance gene related to mcr-1 (and not surprisingly named it mcr-2) in 3 of the isolates.

That’s bad enough.

Of additional concern is that the gene was found on plasmids, which are  smaller pieces of DNA (separate from the bacteria’s chromosomal DNA) that can be transferred readily between bacteria. They found that mcr-2 had a 1200-fold higher transfer frequency compared to mcr-1 on its plasmid, meaning (under lab conditions, at least), that it’s much more adept at moving between bacteria. If it truly can more readily hop to other bacterial species (and therefore potentially more disease-causing bacteria), that’s even more concerning.

Does this mean that we’re seeing a rapid rise in colistin resistance genes?

Probably not. The bacteria from which mcr-2 was isolated were collected in 2011-2012. The increase in recent reports is most likely a factor of an exponential increase in people looking for colistin resistance in bacteria from animals and people. mcr-3 and 4 are probably lurking in the gut of a person or animal somewhere, they just haven’t been described yet.

Is this really a concern?

Yes. While the number of people that will be infected with bacteria possessing these genes will hopefully remain low, these raise the spectre of the “untreatable infections.” When your drug of last resort is gone, you’re in big trouble.

What do we need to do?

There’s no simple answer. A lot involves common sense, good infection control, infection prevention and prudent antibiotic use. These will help reduce the number of infections of any sort, and with fewer infections, along with less (and better) antibiotic use, the spread of resistance genes like this can likely be reduced. They’re not going to be eradicated, but if we can keep them contained, their impact can be lessened.

The authors’ conclusion: Taken together, these data call for immediate inclusion of mcr-2 screening in ongoing molecular epidemiological surveillance to gauge the worldwide dissemination of mcr-2 in both human and animal colistin-resistant Gram-negative bacteria of medical importance.

mcr range

Figure from Xavier et al, Eurosurveillance 2016