Worms and Germs Blog : Animal Health & Diseases : University of Guelph : Ontario Veterinary College : Zoonotic Diseases : Guelph, Hamilton, Ontario

Norovirus sucks. It's been a while since I had it, but it doesn't conjure up fond memories.  A bunch of Canadian tourists returning from Cuba (and presumably all of the other people on their planes) can also attest to the unpleasant nature of this viral infection.

Norovirus in people is (logically) caused by human norovirus. There are some other types of norovirus that infect other species, but the human version predominantly infects people. Predominantly doesn't mean always, though, and other hosts of the virus need to be considered. A recent study published in the Journal of Clinical Virology (Summa et al 2012) looked at whether human norovirus could be found in dogs. Researchers collected fecal samples from 92 indoor pet dogs in Finnish households where people had vomiting and diarrhea or where the dog owner had had close contact with someone with norovirus. Fecal samples were tested for the presence of the virus using molecular tests.

Norovirus was detected in feces of 4 of the 92 (4.3%) canine fecal samples. All positive dogs were from households that had more than two sick people. Additionally, kids were present in all households with positive dogs. Two of the dogs had been sick, with nausea and loss of appetite. Illness in the dogs was pretty mild and only present for one day, and it's not clear whether norovirus was responsible. Fecal samples from owners were only available from one of the positive households, and there the same norovirus strain was found in the owner and the dog.

These results are interesting and indicate that a small percentage of dogs in contact with people with norovirus can shed the virus. The big question is, "what does this mean?" That's not so clear. Finding norovirus in the dogs' feces is one thing. Determining that it's relevant to human (or animal) health is another, and it's important not to over-interpret the results, because...

• The testing that was used detects norovirus RNA, i.e. genetic material from the virus. That means that the virus passed through the intestinal tract. It does not necessarily mean that live virus was present, since this type of testing detects both live and dead virus. Dead virus obviously poses no risk to anyone.
• Even if live virus was being passed in the dogs' feces, the amount of virus coming out the rear end of the dogs isn't known. It might be pretty low and therefore of less concern.
• The relative risk posed by the household dog is a big thing to consider. All dogs that were shedding the virus were from households with multiple sick people, therefore they were already in pretty biohazardous environments with lots of virus being tossed around (in many different ways). This suggests that it may take a lot of exposure for dogs to shed (potentially only a little) virus. Also, it minimizes the relative risk posed by the dog, since if only dogs from severely affected households shed the virus, the dog is only one of many possible sources and probably of lesser risk than exposure to sick people and environmental surfaces they contaminated. Dogs from households with active disease are probably not very likely to encounter lots of other people or dogs (probably less so than the people in the house), therefore limiting their potential role in transmission. There's no evidence that dogs are long-term carriers of norovirus.
  

Does this change what you should do if you have norovirus? Not really. It means you should try to limit contamination of the environment, wash your hands frequently, stay away from others as much as possible and avoid puking on your pets. Maybe we should add "keep your dog isolated along with you," just in case.

Another interesting finding was the association between sick kids and norovirus-shedding dogs. It's further evidence of the "kids are biohazardous" theory. We know that kids are at increased risk of various infectious diseases. At the same time, we have previously shown that contact with kids is a risk factor for dogs shedding Clostridium difficile and MRSA. Whether that's because kids are more likely to be shedding these bugs, they have closer contact with pets, they pay less attention to hygiene or a combination of these isn't clear, but this result isn't particularly surprising. (No, I'm not recommending banning kids from pet-owning households. As parents, we know our kids are effective disease vectors... that's just part of having kids.)

This study doesn't tell us whether pets are sources of human norovirus, and we really shouldn't expect it to. A single study rarely answers all the questions, and good studies sometimes raise more questions than they answer. This is an interesting study and it shows that more work is indicated to clarify the answers to the questions raised above, and to determine whether there is any real concern about dogs and this nasty virus.

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Following reports of a veterinarian warning colleagues and horse owners about West Nile infection in a British Columbia horse, Dr Brian Radke, a Public Health Veterinarian at the BC Ministry of Agriculture, has clarified the situation.

"The BCCDC co-ordinates WNV surveillance for the province of BC including monitoring of mosquitoes, birds, horses and humans. The BC Ministry of Agriculture supplies information to BCCDC on horse cases. In Canada, equine cases of WNV are reportable the Canadian Food Inspection Agency (CFIA).

The CFIA has no reports of WNV consistent with the Prince George horse. Discussions with the veterinary practitioner have clarified that the horse's illness, which occurred in November, was not due to WNV.

The testing discussed in the article was not conducted at the provincial government animal health laboratory. The BC Ministry of Agriculture is following up to determine the nature of the WNV testing and the appropriate interpretation of the test results.

BCCDC WNV surveillance indicates the following:

• In 2011 no humans, mosquitoes, or birds were detected with WNV infection in BC. One horse in the Central Okanagan was reported as positive and that report is under review.
• There have been no positive WNV indicators in the Prince George area.
• In BC, WNV has been detected in southern parts of the province, all below N50 latitude. (By comparison, Prince George is N54 latitude.)
• Risk modelling by BCCDC suggests that Northern BC, including Prince George, experience insufficient sustained heat during the short summer for WNV to amplify and be transmissible by the low density of vector mosquito species.
• The risk modelling also suggests that even in the warmest (that is, southern interior) areas of the province, the risk of WNV infection decreases significantly in September as the vector typically ceases seeking blood meals.

The BC Ministry of Agriculture and BCCDC look forward to working with the province's equine practitioners to interpret WNV testing results and epidemiology to assess the risk of WNV to horses in the various regions of BC. The assessment of risk could then inform decisions about the appropriate interventions for WNV infection in horses in the various regions."

We thank Dr. Radke for the information.

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A Prince George, British Columbia veterinarian is warning other veterinarians and horse owners about West Nile in the province. Little information is available at this point, but the warning is in response to a diagnosis of West Nile infection in a horse from the area. The report calls it a "deadly disease" but it would be more appropriate to call it a "potentially deadly disease," since most horses that are exposed don't get sick, and many sick horses recover. I don't want to downplay the seriousness of West Nile, but it's important to keep it in perspective and make people panic.

The BC CDC has an ongoing West Nile surveillance program because of the obvious concern as this virus has worked its way across North America over the last decade. While it's taken it's time getting to BC, West Nile virus has been identified in the province, and only time will tell whether it becomes a serious health concern for horses or people. The latest update of the BC CDC surveillance data indicates one positive horse, but no positive humans (of 415 tested) or mosquito pools (2282 tested). The one equine case that was documented was from Central Okanagan. The horse had clinical signs consistent with infection, although the severity and outcome are not reported.

It's unclear to me whether this Prince George case is something that's happened just recently or whether the horse was sick. It's pretty late in the year for a mosquito-borne virus, but not impossible in some areas.

Does this report mean that horse owners in BC should be concerned?  Maybe. "Aware" might be a better term.

Horse owners and veterinarians always need to be aware of the infectious disease risks in their area, and areas to where a given horse may travel. Keeping apprised of ongoing West Nile virus surveillance can help determine the likelihood of exposure, but that doesn't mean you can wait until there's a case next door before you do anything. (Someone has to have the first case in an area, and you don't want that to be you.)

Whether or not to vaccinate against this virus depends on the likelihood of exposure and risk aversity. Available vaccines are rather safe and effective (not 100% on either account, like any vaccine, but quite good overall), and vaccination decisions should be made based on a well-reasoned discussion between veterinarian and owner, considering a variety of factors such as where the virus has been found and how much risk everyone is willing to take.

The news report has a quote recommending vaccination in the spring. That's the typical time people vaccinate against mosquito borne diseases, but that's not my recommendation. For me, the goal is to vaccinate so that peak immunity is present at the time when exposure is most likely. West Nile virus is classically a late summer/fall disease, based on mosquito types and their biting patterns. For that reason, I like to see horses vaccinated a little later in the year - closer to the high risk period. Again, it's important to know disease trends in each region to make the most informed decision.

So, horse owners in BC should be aware but not panic. A good discussion about vaccination and about general mosquito avoidance practices should be the first thing that happens.

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Case reports of infections acquired from pets are sporadically found in the human medical literature. A common problem with these reports is the failure to look for true evidence of zoonotic transmission. The typical thought process is "We found this bug in a person, it's most often found in animals, so this person must have gotten it from their pet." Often, this likely is actually the case (although some evidence would be nice). In other instances, like the Pasteurella bone infection described in the Orthopedics paper I wrote about recently, this assumption is probably completely off-base.

Something that is usually missing from these reports is any investigation of the suspected pet. Finding the bacterium in question in/on the pet, and showing that it's the same strain as was found in the person goes a long way to supporting the conclusion that the pet was the source. It's not a 100% guarantee, since you can't say whether it went from pet-to-person or person-to-pet, but with a typically pet-associated bacterium its much more likely to have come from the pet, so finding the same strain in both pet and person is pretty solid evidence. Most case reports don't bother even trying to get this much information (but they still get published...).

A case report in an upcoming edition of Zoonoses and Public Health (Register et al 2012) is another example of a study that provides some information about a potential pet-associated infection, but stops short of the type of proof that is needed. To their credit, the pet wasn't available for testing and they are clear that it's a "possible" case of zoonotic transmission, which puts them a step up on other studies, but it's still too bad the additional information couldn't be reported.

The case report describes an 11-year-old girl with cystic fibrosis (CF). People with CF are at greatly increased risk of respiratory infections, including infections caused by microorganisms that typically don't cause disease in other people. This child had a sputum sample collected during a routine doctor's visit, when she didn't have any signs of respiratory infection. Bordetella bronchiseptica, a bacterium most often found in dogs and cats (and one of the causes of kennel cough (aka canine infectious respiratory disease syndrome) in dogs), was isolated from the sample. When this was explored further, it was revealed that child's family had obtained a new kitten three weeks earlier, and the kitten had signs of respiratory disease.

Unfortunately, the kitten had been removed from the household by the time B. bronchiseptica was diagnosed in the girl, so it couldn't be tested. (They don't say why the family got rid of the cat.) However, the authors at least took it a step further and did some detailed molecular characterization of the bacterial strain they recovered from the sputum sample. Different genetic traits suggested that the strain was feline in origin, and, combined with the fact that the child had contact with the kitten, this provided a little more support to the hypothesis that the cat was the source. It's not proof, but still interesting. They also determined that the B. bronchiseptica strain was missing a gene that's associated with helping cause disease, suggesting it's not as able to make people sick. That might explain why the child was carrying the strain in the absence of disease, although people can carry lots of different bacteria that can potentially cause disease without being clinically ill.

In the end, it was an interesting little report and the authors conclude with a couple of good statements:

"Acquisition of detailed clinical and epidemiological data paired with discriminatory genetic comparison of case isolates and contact isolates is needed to more firmly establish transmission patterns and identify likely contact risks." (A fancier way to say what I said above.)

"...it seems advisable to counsel CF patients regarding adherence to practices that minimize opportunities for zoonotic transmission of B. bronchiseptica from family pets or other potentially infected animals."

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No, not gravy made from bearded dragons (a type of reptile), but foodborne Salmonella with a link to the reptile.

Reptiles are an important source of Salmonella, which is why standard guidelines recommend that high-risk people (e.g. children less than 5 years of age, elderly individuals, people with compromised immune systems, pregnant women) not have contact with reptiles or have them in the house. A report in Zoonoses and Public Health (Lowther et al 2011) highlights another possible risk.

The report describes a Salmonella outbreak that was traced back to a potluck dinner. Nineteen cases were identified, 17 primary cases (people that attended the dinner) and two secondary cases (household members of people that attended the dinner). Overall, 29% of people that attended the dinner got sick. A further 18 people had some intestinal disease but strictly speaking didn't fit the definition for a case (however it is suspected that they were part of the outbreak). Salmonella subspecies IV (a type mainly associated with reptiles) was isolated from the stool of five people, confirming the occurrence of an outbreak.

As is typical, food consumption history was evaluated. Sixteen of the 17 primary cases reported consuming turkey gravy, which was a statistically higher proportion than that of people who did not get sick. The gravy was made at the private home of a person who didn't attend the dinner. This was the only home of the people involved where reptiles were kept. Two healthy bearded dragons lived in the house, in a terrarium in the living room.

The investigation focused on the reptiles, since the Salmonella strain found is typically associated with reptiles, and the turkey (the source of the gravy) had no evidence of Salmonella contamination based on testing. Samples from the environment of the household where the gravy was made were collected, and two types of Salmonella were identified. One of these Salmonella types (Salmonella Labadi, which was different from the outbreak strain) was isolated from one of the bearded dragons, as well as the inside and outside of the terrarium glass, other terrarium surfaces, surfaces around the terrarium, the bathroom sink drain and kitchen sink drain.

A common question that comes up when people have reptiles and high risk people in the house is "If I don't take the critter out of the cage, I should be ok, right?" Unfortunately, that's not true. Human Salmonella infections have been clearly identified in situations where reptiles don't leave the terrarium because (as was the case here), while the reptile may not leave the terrarium, Salmonella often does.

The person who made the gravy said that the bearded dragons had not been out of the terrarium when food was being prepared. A child was responsible for feeding the reptiles and cleaning the terrarium, and was supposed to use the bathroom for terrarium cleaning. However, it was reported that the reptiles' dishes "might have" been cleaned in the kitchen sink during the the day period when food was being prepared for the party.

The overall conclusion was that this outbreak "probably resulted from environmental contamination from bearded dragon faeces." It's a reasonable conclusion. Even though the same Salmonella strain wasn't found in the reptile, it makes sense because the reptiles were the most likely source of environmental contamination in the household, and that was the most likely source of the foodborne contamination. Reptiles can shed various Salmonella strains and they can shed intermittently. It takes multiple samples over time to get a real idea of the scope of Salmonella shedding, and I assume that one or both of these reptiles were shedding the outbreak strain at some point.

How can something like this be prevented, since the standard recommendation of having high risk people avoid contact with reptiles doesn't apply to this type of situation?

• Good hygiene practices should be used when handling reptiles and their environments. In particular, there should be proper attention to hand hygiene after contact with reptiles or their cages.
• Reptiles should not be allowed in the kitchen. Ever.
• Food and water bowls should not be cleaned in kitchen sinks. Terrariums should not be cleaned in kitchen sinks. Ideally, they shouldn't be cleaned in bathroom sinks either. (If possible they should be cleaned outdoors with a hose.)
• Good food handling practices are critical. Here, gravy wasn't re-heated to a high enough temperature to kill the contaminating Salmonella. Adequate re-heating would have prevented this outbreak.

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