#18,369
The USDA has updated their mammals with H5N1 list (excludes livestock), adding 9 more cats (n=115), including 5 more from Hunterdon, NJ (see New Jersey: Hunterdon County DOH Reports 4 More Cats Test Positive for HPAI H5N1 (Ttl=6)).
While 29 new cases appear to have been added to the list, due to backfilling, it is difficult to determine everything that has been added since last week. Among them, however, appear to be:- 7 House Mouse reports (Indiana, Ohio & Missouri)
- 10 Deer Mouse reports (many from Clackamas County, OR in Nov/Dec 2024)
The USDA began tracking H5N1 in mammals in May of 2022, and over the first two years averaged about 100 additions to their list. In early April of last year, that number sat at 214, with only 7 entries during the first quarter of 2024.
Up until that time foxes, skunks, and harbor seals made up the bulk of reports. Cats, and rodents (deer mice, house mice, and black rats) had not made the list.
Fast forward less than a year, and 336 new animals have been added to the list, with 80% of them being either domestic cats (n=115) or rodents (155). The number of wild or captive big cats infected has surged as well.
Given the lack of reports from nearly 1/3rd of the country (see map above), and an understandable emphasis on testing of peridomestic mammals - particularly around poultry and dairy farms - we are undoubtedly only seeing a tiny fraction of the spread of the virus in mammals around the country.
While what happens on farms may take precedence due to its economic impact - and increased opportunities for spillover into humans - understanding what is happening in the wild is still important.
- Last September, in Pathogens: Susceptibility of Synanthropic Rodents to H5N1 Subtype HPAI Viruses, we saw a report that warned that rodents could potentially play a role it its evolution and spread of the virus.
- While last December - in Emerg. Microbes & Inf.: Marked Neurotropism and Potential Adaptation of H5N1 Clade 2.3.4.4.b Virus in Naturally Infected Domestic Cats - we saw isolates from two cats in South Dakota that showed worrisome signs of viral adaptation to a mammalian host.
- And just last week, in Nature Comms: Cross-species and mammal-to-mammal transmission of clade 2.3.4.4b HPAI A/H5N1 with PB2 adaptations, we saw even more evidence of adaptation - and potential mammal-to-mammal transmission - of the virus.
Not so very long ago, HPAI H5 was almost exclusively an avian virus, with only occasional spillovers to humans or other mammals. That is slowly, but perceptively, changing (see Nature Comms: Cross-species and mammal-to-mammal transmission of clade 2.3.4.4b HPAI A/H5N1 with PB2 adaptations).
While it remains unknown whether avian H5 viruses have the ability to adapt well enough to humans to spark a pandemic, they continue to spread - and evolve - at a furious rate.
And we underestimate them at our own peril.
