A-Z Index × Submit A-Z Index × Submit A-Z Index Search Dropdown × Submit Facebook Twitter LinkedIn Syndicate Emerging Infectious Disease journal ISSN: 1080-6059 Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.
We conducted a serologic study of domestic cats near the epicenter of the dairy cattle outbreaks of influenza A(H5N1) in California, USA. Three of the 12 cats sampled within 2 km of farms had neutralizing antibodies against H5N1 virus. Proximity to dairy farms was a statistically significant risk factor for seropositivity.
Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b is emerging in domestic cats ( Felis catus ), presenting urgent public health and animal welfare implications. Historically, cats have not been widely considered important hosts of influenza viruses. However, sporadic infections and outbreaks of avian influenza viruses in cats have occurred for >20 years ( 1 ). The emergence of H5N1 clade 2.3.4.4b virus has resulted in widespread mammalian infections ( 2 , 3 ), including an alarming increase in infections among domestic cats, in which the estimated case-fatality rate is 90% ( 1 ). Although most of those infections emerged from direct bird-to-cat transmission, several recent outbreaks among US cats have involved infected dairy farms ( 4 – 6 ) or links to workers in the dairy industry ( 7 ). Contaminated raw dairy milk ( 5 , 8 ) and raw meat–based diets ( 9 ) have been identified as sources of infection in cats.
Like swine, cats have α-2,6- and α-2,3-linked sialic acid receptors ( 10 ) and can be co-infected with avian and human influenza viruses. Thus, with widespread H5N1 virus infections, a growing potential exists for influenza virus co-infections in domestic cats that could result in viral reassortment and selection for novel human-adapted viruses. Infections resulting from cat-to-human transmission of avian influenza have been documented 3 times in the United States, including in a veterinarian and an animal shelter worker exposed to shelter cats infected with influenza A(H7N2) virus in New York, New York, in 2016 ( 11 , 12 ) and in a veterinary professional exposed to a domestic cat infected with H5N1 virus in Los Angeles, California, in 2024 ( 13 ). Suspected human-to-cat transmission of H5N1 virus also occurred in 2024 in Michigan, resulting in the deaths of 2 house cats ( 7 ). Ten additional cats died from another H5N1 outbreak in 2024 in South Dakota ( 14 ) in which cattle-to-bird-to-cat transmission was suspected.
Although several US dairy industry–related outbreaks of H5N1 among cats have been reported, the resulting seroprevalence of H5N1 virus among domestic cats near affected dairy farms is unknown. Therefore, we performed a serosurvey of domestic cats at the epicenter of the 2024–2025 dairy cattle outbreaks in California’s Central Valley.
An animal welfare organization in Tulare County, California, provided serum samples collected from cats during routine blood draws. Because serum samples from routine blood draws were provided, an ethics review was not required. We shipped aliquots to the University of Maryland (College Park, MD, USA) and the University of Texas Medical Branch (Galveston, TX, USA) and tested them using ELISA and H5 microneutralization assays ( Appendix ). We compared approximate age, sex, weight, and distance to nearest dairy farm between seropos…