Following on the heels of an H7N2 influenza outbreak in cats (and one person) in New York, H5N6 avian influenza has been found in two dead cats in Pocheon, Gyeonggi province, South Korea. This highly pathogenic avian influenza strain has been active in South Korea since November 2016, resulting in the death or euthanasia of more than 28 million chickens and ducks from 606 farms. The affected cats weren’t on a farm, but were found only about 2 km away, so may have visited the farm or potentially be exposed to the virus through wild birds in the area.
These infected cats are less surprising than the New York flu outbreak that has affected a large number of shelter cats. Rare spillover infections of avian flu in other species occur, particularly when large outbreaks are present and there are many opportunities for exposure. Cats are susceptible to a variety of flu viruses and can be exposed by eating infected birds (and sick or dead birds are easier to catch of course). The potential for avian flu to spread to other species, and in the worst case scenario to mutate or recombine with another flu virus to become more transmissible in people (while still causing severe disease), is why there’s such an aggressive response to avian flu outbreaks.
The risk infected cats pose to people is hard to determine. Usually, avian flu is not readily transmissible from aberrant hosts (including people), and close, prolonged contact is required for subsequent cases to develop. That’s like the New York outbreak where only one person has (so far) been identified as infected, and that person had very close contact with large numbers of infected cats.
To some degree, these infected cats should just be considered unsurprising but unfortunate collateral damage of the avian flu outbreak, and nothing to get too concerned about. However, roaming cats in areas where avian flu is present cause concern because they are a potential bridge between the bird population and humans. People who are working or living closely with birds are at highest risk of avian flu. If local cats become infected and roam to other areas, they could expose other people outside of these high-risk groups, and outside of standard outbreak containment and surveillance efforts. The two dead cats in this case may have been feral cats, but the potential for cats to act as a bridge is another reason that pet cats should be kept inside in areas where avian flu is actively circulating.