Cat on bedEmerging problem, newly recognized issue or oddball infection? Recent identification of H7N2 in cats at a Manhattan animal shelter has raised recurring concerns about animal health, human health and the movement of influenza viruses.

As a quick recap, flu viruses are named (in part) based on the genes coding for two important viral proteins, hemagglutinin and neuraminidase. There are several variations of each each gene, and a number is given to each variation. The flu virus strain is then named accordingly: H5N1, H3N2 or, in this case, H7N2.

It’s interesting but not particularly surprising for a flu outbreak to occur at an animal shelter. We know that cats are susceptible to various human and avian influenza viruses. They don’t tend to spread very far since they’re not really designed to live in cats. The fact that this outbreak is caused by an H7N2 virus is interesting. H7N2 influenza is a rarely diagnosed strain, being of avian origin with only a handful of cases diagnosed in people.

Whatever the original source was, at least 45 cats became infected (unclear whether these were all confirmed or only suspected cases), with no cases in dogs or other species at the shelter. Fortunately, as is often the case, the cats didn’t get particularly sick.

People who have been in close contact with the affected cats are being tested. This is an unusual (but interesting) response, since in my experience most often the “wait and see” approach is used, whereby people are only tested if they developed signs consistent with flu. This isn’t often done because of the cost, effort and relatively low likelihood of an action in response to the results. It can provide some useful information, though, and is probably particularly important with a rare strain like this.

The facility is currently quarantined and is being disinfected. Disinfection isn’t a huge component of flu control since the virus doesn’t live too long on surfaces outside the body, and transmission directly from infected individuals (animal or humans) is the main risk. However, it’s an easy(-ish) thing to do, might be of some use in highly contaminated environments, and it also buys time to watch for further cases.

It’s assumed that November 12th was the earliest potential infection date, and health officials are contacting people who adopted cats after that time. The risk posed by a cat adopted a while ago is low to non-existent, since flu virus shedding tends to be very short term. Evaluation of whether people who adopted cats during this time were more likely to report flu-like illness compared to a control group (people who didn’t adopt cats or people who adopted cats outside of this period) would help determine if there was likely any subsequent transmission to household members.

As with most flu outbreaks, with reasonable containment, this should burn itself out. There is no longterm carrier state for influenza, so infected cats (and people) have to encounter a susceptible individual during their relatively short virus shedding period in order to pass on the infection. If that can be stopped, or when all susceptible individuals get infected (and therefore become no longer susceptible), flu should disappear from a closed population like this.