An interesting and frankly somewhat scary report in an upcoming issue of Veterinary Microbiology (Clegg et al 2012) provides further information suggesting that cats might be a source of canine parvovirus infection. This potentially fatal infection, which typically affects young unvaccinated (or inadequately vaccinated) puppies, is a major problem, and outbreaks occur (not uncommonly) in some high-risk populations like shelters.
In the 1970s, a new form of canine parvovirus, CPV-2, emerged and rapidly spread worldwide. That predates my veterinary career but I've heard stories of clinics where you couldn't turn a corner without stepping on a dog that was hospitalized for treatment of parvo, since it was a new disease and vaccines were not yet available. CPV-2 was shown to be able to grow in cat cells in the lab, but not in live cats, so it was generally assumed that dogs had CPV and cats had their own closely related virus, feline panleukopenia virus (FPLV). However, new variants of CPV-2 have emerged over time, and these seem to have a greater ability to infect cat cells in the lab, and disease caused by these strains has been reported in cats both experimentally and in limited real-world situations. However, it was still considered an uncommon event and the role of cats in parvovirus infection of dogs was largely thought to be inconsequential.
Or maybe not.
In this new study, researchers collected fecal samples from 50 cats in a cat-only shelter, and 180 samples from 74 cats at a shelter than housed both dogs and cats. Canine parvovirus shedding was identified in 33% of cats from the cat shelter and 34% of samples from the dog/cat shelter. A concern with a study like this is cross-reaction of tests for CPV and FPLV, but they went a few steps further to confirm that the virus was indeed CPV, not its feline relative. They also showed they could grow the CPV from fecal samples in cells in the lab, which means they were detecting live virus in the animals, not just dead viral bits working their way through the cats' intestinal tracts.
The results are interesting and concerning, since they showed that a pretty large percentage of cats in some situations could be shedding live CPV, making them a potential source of infection for dogs (and possibly other cats).
What makes this even more concerning is the duration of shedding that they identified when they collected samples from the dog/cat shelter over time: cats shed the virus for up to 6 weeks, despite appearing healthy.
This raises concerns about the potential role of cats in the spread of CPV. Cats and dogs don't tend to mix much in parks or outside, but CPV is a very tough virus that can survive for a long period of time in the environment. It's certainly plausible that cats could be depositing CPV-laden feces in the outdoor environment, and since the virus can survive the outdoor exposure and some dogs are notorious poop-eaters, it's a route of transmission that can't be dismissed. Cross-contamination within shelters is also a concern.
The true role of cats in canine parvovirus infection isn't known and it's probably quite limited compared to dog-to-dog spread. However, this study shows that we at least need to be thinking about it and considering cats when dealing with parvovirus problems in shelters and households.
Some things to think about:
- Young puppies should be kept away from cats, especially strays and cats from shelters, until they are properly vaccinated.
- Parvo is one more reason to have good physical and procedural separation between cats and dogs in shelters.
- If a parvo outbreak in underway in a facility, prevention of potential cross-contamination from cats is required.
- If a cat has been in contact with a dog with parvo, it should probably be considered potentially infectious and kept away from susceptible dogs for at least a few weeks.
- Canine parvovirus vaccination is highly effective in dogs. If a dog is properly vaccinated, the risk from cats (or other dogs for that matter) is minimal.