• Avian flu infections in cats are increasing, particularly with the H5N1 clade 2.3.4.4b strain, raising concerns about potential human spillover.
• The virus has infected over 1,000 dairy herds across 17 states in the U.S., and has also been detected in raw milk samples and aged raw cheese.
• Experts are calling for increased surveillance and testing in both animals and humans to better understand transmission events and potential mutations of the virus.

Avian influenza, commonly known as bird flu, continues to spread among animal populations in the United States. The recent increase in avian flu cases in domestic cats, particularly the H5N1 clade 2.3.4.4b strain, has raised concerns among scientists about the potential for zoonotic spillover to humans. The virus has been found in dairy cows across multiple states, raw milk samples, and even aged raw cheese. While human cases remain relatively low and there is no evidence of human-to-human transmission, experts emphasize the need for increased surveillance, testing, and biosecurity measures to mitigate the risk of further spread and potential mutations of the virus.

• What: Avian influenza is spreading among animals in the U.S., with a notable increase in infections among domestic cats. The H5N1 clade 2.3.4.4b strain is of particular concern due to its high case-fatality rate in felines and potential for human spillover.
• Who: Key entities include the CDC, USDA, World Health Organization, University of Maryland scientists, dairy farmers, poultry farm workers, veterinarians, and cat owners.
• When: The current outbreak has been ongoing since March 2024, with a significant increase in feline infections observed in 2023 and 2024. The first human case was confirmed in April 2024.
• Where: The virus has been detected in dairy cows across 17 states in the U.S., as well as in various countries worldwide. Infections in cats have been reported in zoos, animal shelters, farms, and private rural land.

The spread of avian flu is concerning due to its potential to mutate and adapt, increasing its transmissibility to humans. The rise in feline infections, particularly the H5N1 clade 2.3.4.4b strain, highlights the need for increased surveillance and biosecurity measures. Experts emphasize the importance of coordinated testing and data sharing between different departments and agencies. The potential for the virus to enter animal shelters and cause large outbreaks is a significant concern.

"I think the real question comes down to: how much do we want to test animals and people in order to be able to nail down transmission events and really understand how frequently this is happening?"

"As feline-to-human transmission of AIV has been documented, and potential airborne and fomite-mediated transmission implicated, farm and free-roaming cat owners, veterinarians, zoo keepers, and animal shelter volunteers may have a heightened risk of AIV infection during epizootics among birds and mammals."

Avian flu continues to pose a threat to both animal and human health. The increasing number of feline infections, coupled with the virus's ability to mutate, underscores the need for heightened vigilance and proactive measures. Ongoing research, increased surveillance, and coordinated efforts are crucial to mitigate the risks and prevent potential human spillover.