Four more cats die from H5N1 as new report calls evidence for efficient mammal-to-mammal transmission "unprecedented"

Cats are incredibly susceptible to HPAI (highly pathogenic avian flu) H5N1, and they are continuing to die from it. As of May 21, four more cats have died of H5N1 avian flu in the United States, bringing the number to 14 since early Spring 2024. At least 24 cats have died of H5N1 in the last two years

BNO News reports that two of the four most recent deaths include two pet cats in Campbell County, South Dakota who had no connections to poultry or dairy farms or farm animals. The two other cats, both from Michigan (Isabella County and Ionia County), were barn cats at commercial dairy farms and were around cows that were infected with H5N1. In addition to those cats, two opossums on the property also tested positive for H5N1. BNO News further explains:

"Cats are particularly susceptible to H5N1 viruses and the majority of sick cats have been reported at or near affected poultry facilities or dairies," Shilo Weir, a spokesperson for USDA's Animal and Plant Health Inspection Service, told BNO News.

At least 14 cats in the United States have died of H5N1 bird flu since the virus was confirmed in dairy cows in late March. The real number of infected cats is believed to be higher due to limited testing.

Earlier this month, officials confirmed that a domestic cat in Montana was also infected with H5N1 after exhibiting "neurologic signs" and the discovery of a dead skunk on the property. It's unclear if the skunk was also infected.

Scientists are increasingly concerned about H5N1 clade spillovers that have been detected in 30 mammalian species. Many infected mammals, including foxes, bears, cats, and harbor seals, have suffered from neurological issues due to developing encephalitis from the virus. Most recently, these spillovers have affected dairy cattle, which have been found at 51 farms in 9 states.

A group of veterinarians and animal scientists from the College of Veterinary Medicine at Cornell University, Texas A&M Veterinary Medical Diagnostic Laboratory, Ohio Department of Agriculture, and the Southeast Poultry Research Laboratory at the USDA Agricultural Research Service in Athens, GA, in a preprint study published today at bioRXiv ("The Preprint Server for Biology"), calls this spillover into dairy cattle and the evidence for efficient mammal-to-mammal transmission "unprecedented." These researchers analyzed genome sequences from dairy cows, birds, domestic cats, and a raccoon from 9 dairy farms affected by H5N1 this spring, including 5 in Texas, 2 in New Mexico, 1 in Kansas, and 1 in Ohio. They found evidence of an emerging "B3.13 genotype" in all 91 sequences. They also observed epidemiologically that raw milk was fed to cats at those farms. Their phylogenomic analysis coupled with their epidemiological evidence:

indicate cattle-to-cat and cattle-to-raccoon transmission. These observations indicate that complex pathways underlie the introduction and spread of HPAI H5N1 in dairy farms, highlighting the need for efficient biosecurity practices and surveillance efforts in affected and non-affected farms.

They end the paper with an urgent call for action:

This newly acquired viral property is concerning as it can lead to adaptation of the virus which may further enhance virus infectivity and transmissibility in other species, including humans. Therefore, it is imperative that robust and continuous surveillance and research efforts be established to monitor the circulation, spread, and adaptation of the HPAI H5N1 virus in this new host species.

Click here to read the entire study.

Previously: Raw milk lovers are spinning the government's H5N1 warnings into a conspiracy theory
Mysterious duck die-off in Idaho, new H5N1 worries
Here's the latest on H5N1—avian flu—and some resources tracking the virus