Seropositive cats around HPAI Infected Dairy Farm
#19,268
We've known for more than 2 decades that cats - both large and small - are susceptible to HPAI H5 infection (see 2004 CIDRAP Report) and have seen scattered reports over the years (see 2015's HPAI H5: Catch As Cats Can).
Until relatively recently, those reports were fairly rare, and mainly came from zoo animals fed on a diet of raw chicken. But since the emergence of a new, more transmissible clade 2.3.4.4b H5N1 virus in 2021, the number of companion animals (and other mammals) reported to be infected has risen sharply.
While undoubtedly underreported, more than 20% of all of the mammalian wildlife detections reported in the United States (180 of 813 USDA reports) over the past 4 years have been among felines.
Many have been reported in and around dairy and poultry farms (see EID Journal: HPAI A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024).
While many cats infected with HPAI sicken and die, others - based on seroprevalence studies (see Eurosurveillance: (HPAI) H5 virus Exposure in Domestic & Rural Stray Cats, the Netherlands, October 2020 to June 2023) - are likely only mildly affected and survive.
Previously, we've seen evidence of cattle-to-bird-to-cat transmission of avian flu, large outbreaks in animal shelters suggesting cat-to-cat transmission (H7N2), and limited evidence of cat-to-human transmission (see here and here).
All of which brings us to a new dispatch, published yesterday in the EID Journal, which reports a 25% seropositivity rate among (n=12) cats sampled within 2 km of infected dairy farms, while no cats were seropositive further away (n=61).
While this is just one small, geographically limited, study the authors state: "Proximity to dairy farms in counties experiencing outbreaks may be a risk factor for H5N1 spillover to indoor and outdoor domestic cats."
I've only posted the highlights, follow the link to read the report in its entirety.Volume 32, Number 9—September 2026
Dispatch
Seroprevalence of Influenza A(H5N1) Virus in Domestic Cats at Epicenter of Dairy Cattle Outbreaks, California, USA, 2024–2026
Ian G. Bemis, Ismaila Shittu, Jacob F. Gomez, Esther A. Fadaka, Sofia Perez, Gregory C. Gray, and Kristen K. Coleman
Abstract
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.
(SNIP)
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.
(SNIP)
During December 2024–March 2026, we collected 73 serum samples from indoor and outdoor cats (Figure 1) within 9.7 km (6 miles) of >1 dairy farms (mean 4.7 km [2.9 miles]). Among the 73 cats, 3 tested positive for both influenza A virus nucleoprotein antibodies and neutralizing antibodies against H5 clade 2.3.4.4b. One indoor-only and 1 outdoor feral cat had neutralizing antibody titers of 1:160, and 1 indoor-only cat had a titer of 1:640, indicating strong positivity and 100% agreement between the ELISA and microneutralization assay. All negative samples had titers of <1:20.
Three (25%) of the 12 cats sampled within 2 km (1.24 miles) of dairy farms were seropositive for H5N1 virus (Figure 2), yielding an overall seropositivity rate of 4.1% for all surveyed cats. Seropositive cats had a mean distance to the nearest dairy farm of 1.34 km (0.8 miles), compared with 4.83 km (3 miles) for seronegative cats (p = 0.014) (Figure 3). Average age of surveyed cats was ≈1.6 years (range ≈3 months–4.9 years); 60% were female and 40% male. Age and sex were not significantly different for seropositive and seronegative cats. Of the 73 cats surveyed, 68 (93%) were in rural areas and 5 (7%) in urban areas. All seropositive cats were in rural areas. No indoor cats were fed raw meat or dairy.
(SNIP)
Conclusions
Avian influenza A(H5N1) clade 2.3.4.4b is an emerging threat to domestic cats and public health. We report a 25% seropositivity rate for the virus among domestic cats within 2 km (1.2 miles) of dairy farms in the epicenter of the H5N1 cattle outbreaks in California during 2024–2026. Proximity to dairy farms in counties experiencing outbreaks may be a risk factor for H5N1 spillover to indoor and outdoor domestic cats. Our research provides insight into potential H5N1 virus sources and transmission routes among domestic cats in the United States, for which data are scarce. Our results may help refine public health guidance on the prevention of avian influenza in cats and set the stage for future studies.
Although only 3 seropositive cats were identified in our study, their closer proximity to dairy farms compared with seronegative cats is an important epidemiologic finding.
(SNIP)
Our study highlights a critical gap in companion animal surveillance and might be helpful to health agencies as they seek approaches to mitigating this emerging infectious disease threat. Proximity to dairy farms was a risk factor for H5N1 spillover to cats in our study. However, cattle-to-cat transmission of H5N1 virus is a relatively new phenomenon, and most cat infections reported in the literature over the past 20 years have been from bird-to-cat transmission (1). To assess the in situ risk for human-adapted reassortant influenza viruses emerging in cats, future work is needed to characterize the seroprevalence of human influenza viruses in cats and avian influenza viruses in cats near outbreaks in poultry and wild birds. Cat surveillance studies also could provide insight into nearby H5N1 outbreaks that have yet to be discovered, fully investigated, or contained.
