An initial analysis today from Poland’s National Veterinary Institute of nine viruses from cats infected with H5N1 avian influenza suggests they are related to viruses found in the country’s poultry and wild birds, according to a statement translated and posted by Avian Flu Diary, an infectious disease news blog. The sicknesses and deaths in cats have been reported from a wide geographic area, with some noted in indoor cats, making the source of the virus unclear.

The report said the viruses belong to the same genotype and are most closely related to a sample collected in June from a white stork. The genotype was seen during the peak of the 2022-23 season and was detected mainly in poultry in Wielkopolska province and in wild birds in multiple parts of Poland.

The report didn’t note any mutations that may make the virus more adapted to mammals. Scientists noted that the feline H5N1 viruses they have examined so far came from a single unidentified source and that more detailed genetic analysis is under way to better gauge the zoonotic potential.

CDC updates H5N1 technical report In other avian flu developments, the US Centers for Disease Control and Prevention (CDC) recently updated its technical information on H5N1, which covers the latest sporadic infections in humans and outbreaks in wild birds, poultry, and other animals. (The document, dated June 30, doesn’t include information on the H5N1 detections in Polish cats.)

The CDC said the H5N1 viruses currently circulating in wild birds and poultry don’t have the ability to easily bind to human upper-airway tract receptors. Though outbreaks in US poultry flocks have declined substantially over spring and summer, the H5N1 strain continues to circulate in wild birds, posing an ongoing transmission threat that requires close monitoring.

Regarding H5N1 in mammals, the CDC said data suggest the virus may evolve to replicate more efficiently in the respiratory tract, but so far the changes haven’t been linked to increased transmissibility in humans.