A few news articles have reported infection of two cats with the H1N1 flu virus. These are the first feline cases reported in Canada, but similar cases have been reported elsewhere, so it’s reasonable to assume that there have been previous undiagnosed feline cases in Canada. Nevertheless, it’s useful information.

Unfortunately, the new reports are very minimalistic in their details – not quite "cat-flu-dead" but pretty close. Information like what clinical signs the cats had, whether there were infected people in the household first, how infection was diagnosed and how the virus strain was confirmed would be useful.

Cases like this always raise a few questions:

What’s the risk to people in the household?

• Pretty limited. We don’t know if infected cats are able to spread the H1N1 virus (though we know that cats experimentally infected with the H5N1 flu shed enough virus that they could pose a risk).
• Nonetheless, it’s important to consider the household disease dynamics. From where did the cat get H1N1? From a person. With what people do most cats almost exclusively have contact? People in the household. So, if the cat was infected, it was probably infected by someone in the household or someone who visited the household, both of which pose a greater risk to other people in the household than the cat.

What’s the risk to the cat population?

• Pretty limited for a few reasons. Most cats don’t tend to have contact with that many cats outside of the household, and the flu virus is shed for a short period of time.
• Cats are also not very susceptible to the virus, so an infected cat would have to be shedding appreciable amounts of virus, have an encounter with a susceptible cat during the short time it’s shedding virus, and then this low-likelihood scenario would have to repeat itself in order for the virus to establish itself in the cat population.

Can cats be a source of new flu viruses?

• In the big picture, this is the main concern. Any species that can be a host for a human flu virus and other flu viruses is a concern because of the potential that infection with multiple viruses at the same time could lead to creation of a new virus – one that is still able to infect people, but is different enough that people don’t have any immunity and current vaccines don’t work (which means it could potentially make a lot of people sick very rapidly).
• However, the risk of this scenario is exceedingly low in cats since H1N1 infection in this species is very rare, and infection of cats by other flu viruses is ever more rare.  Therefore, the odds of concurrent infection AND reassortment of the viruses AND transmission to a susceptible host that can further spread the virus is are extremely remote.