cat-and-dogPerhaps unsurprisingly, canine H3N2 influenza has been found in a group of cats in the US. Canine H3N2 influenza is the strain that emerged in the US last year. It was likely imported (in a dog) from South Korea, and then spread through many parts of the country. As with H3N8 canine flu, we’ve been waiting for H3N2 to show up in Canada, but the border seems to be holding strong and neither canine flu virus appears to have established itself up here.

Cats are susceptible to influenza viruses from other species (including humans) and spread of canine H3N2 from dogs to a cat has previously been reported, and occasional feline infections were known to occur in South Korea. Most recently, the Wisconsin Veterinary Diagnostic Laboratory diagnosed H3N2 influenza in multiple cats at an animal shelter in northwest Indiana. Finding H3N2 in cats, particularly those in a high risk population like a shelter, isn’t really surprising. However, it is concerning, as it is yet another potential cause of disease in cats. It also creates the potential for cats to act as sources of infection of dogs, other cats or potentially other species. The risk of spread from cats (particularly to animals other than dogs) is probably pretty low, since infections in cats will presumably continue to be rare and (at least outside of shelters) cats tend to have limited contact with large numbers of other cats or other animals.

One good thing about influenza is that the virus is only shed for a short period of time. Infected animals (or people) don’t carry the virus for long after getting infected, so it’s easier to contain the pathogen in a shelter or elsewhere. That’s in comparison to other diseases with which some infected animals will become long-term, silent carriers that can spread the causative pathogen to others for a long time. With flu, we can concentrate efforts over a short period and have a good chance of containing it in a given population. The affected shelter has quarantined infected animals, to prevent them from taking flu with them when they are adopted. The article I read doesn’t mention if other adoptions have been suspended. Situations like this need to be handled on a case-by-case basis. If the virus is well contained to a group of known infected animals, life as normal (with some enhanced infection control practices) can go on in the rest of the shelter. If it’s not confidently contained, short term cessation of adoptions is often a good idea, to buy some time to get things under control.

While the fact that flu is shed only for a short time helps, the fact that infected animals often shed large amounts of the virus in the 24 hours before they become sick is a problem. That means that there can be apparently health but infected (and infectious) animals in a group. That’s why confidence in containment is crucial. You can’t just go in every day and say “that cat looks healthy so it can’t be shedding influenza.” You have to stop the cycle of transmission and contain the animals that were exposed, whether they look healthy or not.

What does this mean for the average cat owner?

Not much. The odds of most cats having a close encounter with an infected dog are very low. Cats in shelters are at highest risk. Cats in households are most at risk if a co-habitating dog develops influenza. Controlling canine flu in dogs is the best way to prevent it from infecting cats.

A few general tips, though:

  • Ideally, any cat adopted from a shelter should be quarantined for a short period of time at home after adoption. That’s not just a flu thing, but is useful for a variety of microbes the cat could bring home with it. If other animals are in the household, that’s tough, but limiting direct contact as much as possible for a few days is ideal.
  • I’m not a fan of cats getting outside at all, for many reasons, but if a cat is adopted from a shelter and is to be an indoor-outdoor cat, it should be kept as an indoor cat for the first week or two. That helps reduce the potential for transmitting any shelter-associated diseases to animals in the area.
  • Keep sick animals away from other animals… influenza or otherwise. Common sense, but not necessarily commonly done. If a dog has signs consistent with influenza, it should be keep at home to reduce transmission of the virus.
  • Vaccination of dogs should be considered in high risk situations. That would include dogs in areas where the virus is circulating, dogs whose lifestyles have them in frequent contact with other dogs, and dogs that are likely at higher risk of severe disease if they get influenza (e.g. dogs with underlying heart or lung disease). Vaccines for cats are not available and off-label use of the canine vaccine is not recommended.

H3N2 has established itself pretty well in the US dog population, so this will not likely be the last spillover infection in cats. It’s not a huge deal, but anytime we see influenza moving between species, we get a bit concerned.