#18,341
Over the past 2 weeks we've seen two reports from the Oregon Department of Agriculture (ODA) (see here, and here) on the H5N1 infections and deaths of 3 cats linked to eating raw commercial cat food.
The Oregon H5N1 dashboard - (see screenshot as of 10 am EST today) - lists only 6 cats infected in the state, and only one of those from Clackamas county.
But today the USDA updated their H5N1 listing, which adds 6 more cats from Clackamas County, along with 4 other cats from California, Kansas, New Mexico, and Colorado. This brings the official count to 99 domestic cats (11 from Oregon) along with more than 5 dozen captive and wild `big' cats (bobcats, mountain lions, tigers, etc.).
Combined, felines make up the largest percentage (31%) of the mammals on the list, followed by rodents (21%), and foxes (20%).
The latest additions to the list include 10 cats and 1 house mouse. All of these numbers, however, are expected to be substantially undercounted.
Three months ago, in Emerg. Microbes & Inf.: Marked Neurotropism and Potential Adaptation of H5N1 Clade 2.3.4.4.b Virus in Naturally Infected Domestic Cats, we looked at a report on the HPAI H5 infection of a house full of domestic cats (n=8) in South Dakota last April.
Isolates from the two cats that were tested showed signs of viral adaptation to a mammalian host. The authors wrote:
Cat H5N1 genomes had unique mutations, including T143A in haemagglutinin, known to affect infectivity and immune evasion, and two novel mutations in PA protein (F314L, L342Q) that may affect polymerase activity and virulence, suggesting potential virus adaptation.
Dead cats showed systemic infection with lesions and viral antigens in multiple organs. Higher viral RNA and antigen in the brain indicated pronounced neurotropism.
Until recently, HPAI H5 was pretty much just an avian virus, with only occasional spillovers to humans and a few cats unlucky enough to be fed a diet of raw chicken. But starting in 2021 we began to see reports of numerous spillovers into a much wider range of mammals.
As the HPAI H5 virus continues to find new mammalian hosts it is likely to become more deeply entrenched in our shared ecology, increasing the risks that it will find new evolutionary pathways that were unavailable to it when it was primarily a disease of birds.