I’ve spent a lot of time talking to the press this week about H1N1 and pets. One question that has come up repeatedly involves concern about the potential for this virus to mutate because of its presence in pets. This largely relates to the general knowledge that pigs are potentially important "mixing vessels" for influenza viruses.
H1N1 infection of cats carries almost no risk of a significant mutation. For this to happen, the animal must be infected with two different influenza viruses, and those viruses must recombine so that a new virus containing parts of each of the parent viruses is produced. This virus must then be able to infect a new host and be transmitted. Pigs are a concern because they can be infected by various influenza viruses (from humans and birds, as well as swine-origin viruses), and they tend to live with many other pigs so that the transmission cycle can be started. This isn’t the case with cats.
Cats don’t have their own influenza virus that is in circulation. Therefore, it’s very unlikely that a cat exposed to H1N1 already has a different influenza virus in its system. Even if a cat was infected with a different flu virus (which is exceedingly unlikely) and this virus recombined with H1N1 (which is unlikely even if the two viruses were present), your average cat doesn’t have much contact with different individuals, human or animal, and it’s quite possible that the virus would just die-out in that animal.
While we don’t want to ignore some of the issues regarding H1N1 in pets, such as the potential for pet illness and the unproven possibility that they could transmit H1N1 to other people, we need to keep the concerns in perspective. The risk that pets pose to people is much lower than the already very low risk that people pose to pets, in terms of H1N1 influenza.