Two recent papers have raised concerns about cats in households with cystic fibrosis (CF) patients. People with CF are at high risk for a range of complications because of their condition and the treatments that are required. Some complications can be life-threatening, so there’s lots of research into factors associated with disease in people with CF.
One of the recent studies (Morrow et al. Journal of Pediatrics 2014) looked at 703 kids with CF. As is fairly consistent with the general population, 47% lived with one or more dogs and 28% with one or more cats. Dog ownership was not associated with problems, but cat owners had an increased risk of developing nasal polyps. Nasal polyps are a common problem in people with CF, thought to be caused by allergy, infection and/or chronic nasal congestion. If there’s truly a link with cats, it’s logical that allergies would play a role. When analysis combined dogs and cats, pet owners were twice as likely to report wheezing compared to non-dog/cat owners; again, likely an allergic, not infectious, issue.
Fortunately, wheezing and polyps aren’t typically severe complications. A different situation is presented in a separate case report in Pediatric Respiratory Reviews (Pabary 2014). It describes a child with CF who had difficult-to-control symptoms that were thought to be exacerbated by a cat allergy. The child only improved when the cat was removed from the household.
Does this mean that pets should be removed from households with CF patients?
No, but it means that the cost-benefit balance needs to be considered. As the Morrow et al. paper states "Prospective studies are needed to confirm these associations and the potential psychosocial benefits of cat and/or dog ownership." Figuring out whether these relationships are real (i.e. causative) and determining what the risk of these complications means for an individual person compared to the potential benefits is the key. It’s not easy, and the cost-benefit will vary between households. That’s why there needs to be conversations between patients and their families, their healthcare provider(s) and their veterinarian. The Pabary case report indicates that pet removal is sometimes required, although that’s a rare situation - pet removal/surender needs to be very carefully considered and should not be a knee-jerk reaction (as it all too often is).
Photo credit: Tracy (click image for source)
West Nile virus (WNV) infection has been identified in a horse in Colorado. It's not really a surprise. West Nile virus is one of those pathogens that we know is coming back every year, we just don't know exactly when. The date of return varies a bit from year to year, but tends to be fairly consistent within a region (e.g. if West Nile cases started to crop up in a certain state in mid-August last year, they are likely to start again at roughly the same time this year).
The timing of onset of WNV cases depends on a few things, including WNV circulation in birds, climate and mosquito populations. The latter is quite important since only certain mosquitoes like to bite both birds and mammals. These particular mosquitoes species (called bridging vectors) are the concern, since they are more likely to bite an infected bird, and then possibly transmit the virus to a horse (or human) if they bite them next. Mosquito populations aren't the same all year and in all regions, which explains in part why WNV cases don't start earlier in the year, and why there are some major regional variations in disease despite the widespread presence of mosquitoes.
In Ontario, I suspect we have a few more weeks before we get the first reports of cases for 2014, but the WNV season is approaching here as well.
Photo credit: Rennett Stowe (click image for source)
MERS-CoV, the Middle Eastern Respiratory Syndrome coronavirus, continues to cause infections (often fatal) and confusion. For a while now, there's been speculation that camels are the source of this virus, based in part on how commonly antibodies against the virus (or a related virus) are found in healthy camels. It always seemed strange, though, for camels to be the ultimate source, leaving lingering questions about whether there is another source or where camels got exposed to the virus in the first place.
Some have focused their attention on bats (which were ultimately the source of the related SARS-coronavirus). A recent paper in the Journal of Virology (Corman et al 2014) helps answer some of those lingering questions questions. The researchers found a coronavirus in the feces of a South African Neoromicia capensis bat. When they looked at the sequence of the virus' genome, it was quite similar to that of MERS-CoV - close enough that the two viruses would be considered the same species. There were some differences, though, indicating there appears to be a "bat type" and a type that infects people and camels.
Relatedness is one thing, but figuring out how viruses are different and when they diverged is important (i.e. did the camels get the virus from the bats, or did the bats get it from the camels?). From an evolutionary standpoint, the bat virus "roots" the phylogenetic tree of human and camel MERS-CoV, meaning that when the different viruses are shown in their "family tree" based on their genetic makeup, the bat coronavirus is the one that comes up at the common ancestor. So, it appears that MERS-CoV originated from this bat virus.
The genetic relatedness of these viruses, the fact that the bat virus appears to be the ancestor, and the evidence for circulation of MERS-CoV in camels for at least 20 years suggests that:
- The virus jumped from bats to camels in the southern part of Africa a few decades ago,
- It was imported to the Arabian peninsula (since that is a common route of camel movement), and
- It recently started to infect people.
There was also the suggestion that camels may be a "mixing vessel" for different coronaviruses, like pigs are for influenza viruses, but I think that's pretty speculative.
For me, a few questions remain:
- Why is MERS not detected in southern Africa, if that's where the related virus is present in bats and where it presumably made the jump to camels?
- Why has MERS only recently been identified in people when its been present in camels for a few decades?
As is typically the case with infectious diseases, a few nice answers lead to many more questions. Presumably, lots of camels, bats and other species will continue to be tested in Africa and the Middle East to see what other information can be learmed.
Unfortunately, Naegleria fowleri, more popularly known as the "brain-eating amoeba," is in the news again. Sadly, the latest case is a 9-year-old Kansas girl that died recently from N. fowleri infection. It’s still an extremely rare disease but it’s still a significant concern because infection is almost always fatal.
Naegleria fowleri is a single-celled organism that lives in fresh water, and likes it warm. It grows fastest to 42C (~107F), but about 25C (77F) or higher is warm enough for the amoeba to reproduce. That’s why most cases have been identified in Florida and Texas, and there are concerns that climate change may help expand its range.
People are infected when water contaminated with the organism enters the nose. Not surprisingly, most people are infected while swimming or diving in lakes and rivers. After entering the nose, the amoeba makes its way to nerves and then migrates to the brain, where it essentially "eats" brain cells. Death usually occurs a few days after the onset of disease.
Since people aren’t the only ones exposed to water, a logical question is can other species be infected by Naegleria fowleri? More specifically, can dogs be infected? Many dogs spend a lot of time outdoors and in the water, and could therefore be exposed.
For example, a couple of weeks ago, we were at a cottage for vacation. Our dog Merlin is a pathetic excuse for a Labrador since he’s too chicken to swim, but he still likes to wade in the lake and stick his nose in the water. So, what’s the risk to him (ignoring the fact it’s still up in the air whether he has much of a brain to target)?
Can dogs be exposed?
Certainly, dogs can be exposed to the amoeba. If it’s in the water and people can be exposed, there’s no reason dogs would be any different in that respect. The risk of exposure varies greatly by geographical region. Around here, the risk would be exceptionally low given the water temperature. So, Merlin and his microscopic brain are presumably safe. Even in warmer waters, the risk of exposure would still likely be very low.
Can dogs get sick?
We don’t know. A few different animal species are known to be susceptible, but there are no reported canine cases (yet). The disease is very rare in people, and a person is much more likely to get diagnosed than a dog, in which testing would be less common. It’s also not an easy infection to diagnose and it would require testing of the brain after death. Most dogs that die of neurological disease don’t get tested for something like this. So, I don’t think we can rule it out, but I also don’t think it’s a high-risk situation.
Should anything be done?
It’s hard to say. It’s a rare to non-existent problem in dogs. My general line is that common sense must prevail, but you never want to be the first case of something. Thinking about the risk of disease, what can be done and whether those measures have a realistic chance of doing anything is the key.
Here’s what’s typically recommended for people:
- Use nose clips when in high-risk waters (not going to happen for dogs)
- Avoid putting your head under water in high-risk areas (ditto)
- Avoid stirring up sediment in the water (also probably not going to happen)
- Avoid going in the water during periods when water temperatures are high (this one’s practical)
Bottom line for me: life carries some degree of risk. We have to live with that and we can’t eliminate it all. The lack of evidence that this is a significant problem makes it hard to recommend any disruptive measures.
If Naegleria fowleri is known to be present in a water supply, stay away (for you, as much as the dog). Beyond that, enjoy the summer.
Plague… it’s a term that typically conjures up images of the devastating "Black Death", the pandemic that killed 75-200 million people in Europe back in the 14th century. Yet, it’s not just a historical disease. Plague is still present in a variety of small mammals in different regions worldwide (see map), including parts of the US, with periodic reports in Canada.
A recent case of plague in a Colorado man has attracted a lot of attention. The individual developed the pneumonic form of the infection after his dog died of the same disease. It’s suspected that he was infected from a flea that fed on the infected dog, and then bit the man. However, I don’t think you can really rule out the potential for direct transmission of the bacterium, Yersina pestis, from the dog. Fortunately, despite developing pneumonic plague (the form in which the bacterium infects the lungs, and the deadliest form of Y. pestis infection), it seems that he’s recovering. Plague is treatable with antibiotics, but it is critical that treatment be started as soon as possible or it can be fatal.
Transmission of plague from pets to people isn’t new. However, most often it involves cats that get infected while hunting rodents carrying infected fleas. Cats can develop plague, and then people caring for them (e.g. owners, veterinarians) can acquire the infection.
This case highlights a few important points:
- Plague is still around. People living in areas where plague is present need to be aware of the risk, even though it's very low.
- Pets get infected from contact with infected rodents, either directly or from their fleas. Keeping pets away from wildlife (e.g. keeping cats indoors, limiting free-roaming of dogs) can reduce the risk of exposure.
- Sometimes, knowing the cause of an animal’s illness is very important for human health. Knowing that a pet had plague would greatly speed up consideration of plague in anyone who became sick and had contact with the animal.
- Flea control can help reduce the risk of many diseases, including plague.
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.
Camels are getting a lot of bad press on the infectious disease front lately. There’s been the ongoing question of their role in the epidemiology of the very serious Middle Eastern Respiratory Syndrome coronavirus (MERS-CoV). This enigmatic virus (like the similarly deadly SARS coronavirus) is a tremendous public health concern, with high deaths rates in infected people, and its origins remain unclear. Recent studies have found the MERS-CoV virus in camels, and that, along with finding that a large percentage of healthy camels harbor antibodies against the virus, has lead to suggestions that camels might be the natural hosts for the virus. (They could still be innocent bystanders, infected from the same source(s) that infects people, but evidence implicating camels is increasing.)
On top of that, H3N8 equine influenza virus has recently been found in camels from Mongolia. The camels weren’t sick, but it raises some interesting questions. The H3N8 equine flu virus has been relatively stable for decades, with only minor changes compared to the degree of variability found in typical human influenza viruses. While there’s lots of concern about influenza viruses moving to humans, this particular one hasn’t raised much attention. It made the jump to dogs a few years back, resulting in emergence of H3N8 canine influenza, but not much remarkable has happened with it outside of horses. Presumably, the finding of H3N8 flu in camels is a result of transmission of the virus from infected horses. However, what remains to be seen if whether this virus can/will cause problems (e.g. illness) in camels, whether it frequently moves from horses to camels, and whether camels can then infect horses or other species.
Presumably, these two issues (particularly the MERS-CoV problem) will lead to more attention to various infectious diseases in camels. In general, the more you look, the more you find, so it’s likely that other potential infectious disease issues will be identified. Whether this means there are truly emerging issues in camels or whether some of these issues have been going on under the radar for some time remains to be seen.
Photo credit: S. Taheri (own work)(click image for source)
That’s a great title that I can’t take credit for. A colleague (and regular supplier of papers for blog posts) Dr. Stephen Page send me a paper from the Journal of Clinical Microbiology with a more convoluted title “The Capnocytophaga canimosus isolate that caused sepsis in an immunosufficient man was transmitted by the large pine weevil Hylobius abietis” (Tuuminen et al 2014).
I often talk about the bacterium C. canimorsus, and any mention of it is usually greeted with either blank stares or the "what the heck was that bacterium called?" look. It’s an obscure bacterium that’s found in the mouths of pretty much all dogs, as well as some other species. While it rarely causes disease, when it does, it can kill quickly.
This report is noteworthy from a few standpoints. One is the source of infection, as it was associated with a pine weevil, an insect. Insects have not been linked C. canimorsus infections in the past, although I’d wager that little is known about their normal mouth microbiotas. The affected person was a 44-year-old sawmill worker in Finland, with no remarkable health problems. That’s important because C. canimorsus infections almost always occur in people without a functional spleen, alcoholics or people with compromised immune systems. He seemed to have none of those risk factors. While this has been reported before, it’s quite rare.
So, should pine weevil bites be added to the list of things that indicate a need for high-risk people to seek medical care? Well, that seems extreme but it shows the unpredictable nature infectious diseases.
Another question, though: where did the insect get the bacterium (i.e. where did the bug get the bug)? Does C. canimorus actually have a much broader host range? Did this insect recently bite a dog in the mouth? Or, did the person have some other form of exposure? The paper’s title is probably more definitive about the source of infection than it should be. He didn’t own a dog or report being bitten, but could C. canimorsus have been inoculated into the bug bite lesion from some other source?
Who knows? Sounds like a good excuse for a field trip to Finland to look at the microbiota of the pine weevil.
Photo credit: http://en.wikipedia.org/wiki/Hylobius_abietis
A couple days ago, I was talking to a vet who's trying to manage a strangles outbreak on a farm. In many outbreaks, the biggest hassles are dealing with horse owners, not the disease itself. Strangles, infection by the bacterium Streptococcus equi subsp. equi, is a highly contagious disease but one that is relatively easy to control if things are done right.
The critical variable is whether people will do things right.
There are many issues that result in prolonged outbreaks at single facilities or spread of strangles from farm to farms, but two are quite common, recurrent problems.
1. Unwillingness of people to skip shows during the outbreak. I understand the desire to go to shows, since the show season may be short and shows are what people look forward to all year. However, despite the fact that it's clearly unethical for people to take a horse to a show from a barn where a strangles outbreak is underway, it happens all the time. That's probably one of the most important ways strangles is spread during the show season.
2. People moving horses to other barns. It's not uncommon for there to have already been one or more people flee the barn by the time I'm involved in an outbreak investigation, and I've seen multiple situations where one-farm outbreaks have turned into regional outbreaks because of this. This response is sometimes because individuals want to try to avoid the outbreak (although their horse may have already been exposed, making it too late), or to avoid any restrictions that might be put on the barn and movement of horses therefrom.
Both situations are common, but ethically are unacceptable. If a person knows that his/her horse is on a farm where strangles is present, the animal is considered infectious until proven otherwise.
How can these problems be prevented?
1) Boarding contracts that stipulate owners will stay on the farm in the event of an outbreak (maybe not easy to enforce, but at least addresses the issue up front).
2) The carrot: Emphasizing that with a good infection control response, if a particular horse has not been exposed, it probably won't be, and if it has been exposed, it's a risk to others. Either way, keeping it on the farm is the best for it and for others.
3) The stick: Reminding owners that they know their horses might have been exposed to strangles. If they take a horse somewhere and infect other horses, they might be (or should be) liable for any costs and losses associated with those subsequent cases. Infectious diseases are an inherent risk of life and are not always preventable, but when someone knowingly creates a high risk situation (and that situation was avoidable), legal consequences may ensue.
A reader recently posed a question about the potential risk of rabies virus exposure from running over a rabid animal. I get the "can I get rabies from touching roadkill?" question regularly, but this person had a different concern.
“The other day I accidentally plowed right over an already-dead animal in the road. My air conditioning was blasting right on my face at the time. I am sure that something could have splattered under my car. Moreover, there could be a weakness or opening in my AC system that would allow the rabies virus to enter.”
We typically shy away from saying "never" with infectious diseases, but this would be as close to a "never" situation as you can get.
For this to be a concern:
- the animal would have to be rabid
- brain tissue and saliva containing rabies virus would have to be aerosolized
- virus particles would have to make it past the air filters...
- ...and then come into contact with mucous membranes (e.g. mouth, eyes) or open skin lesions.
That’s just not a realistic concern. Non-contact-associated transmission of rabies is very rare and concerns are mainly limited to labs where large quantities of virus are manipulated, and people entering highly-infected bat caves.
Rabies is not an airborne virus, and beyond direct contact concerns would only relate to aerosol/droplet transmission, something I describe as "splash zone" transmission. Even with poor or absent air filters in the car, droplets aren’t going to make it through the whole ventilation system to the driver's body.
The reader's final question: “Or are you laughing while reading this?”
Trust me, I get stranger questions on a daily basis.