H5N1 cases in a Washington cat and Dutch cows sharpen vigilance

H5N1’s reach into mammals keeps widening, and two recent developments, one involving a dead cat in Washington state and the other involving dairy cattle in the Netherlands, underscore how often veterinarians may be the first to spot the problem. In a February 2, 2026, update, Worms & Germs author Scott Weese pointed to a Washington outdoor cat that tested positive for H5N1 and to new reports from a Dutch dairy farm where five cows ultimately tested positive for H5N1 antibodies after an infected farm cat prompted the investigation. (wormsandgermsblog.com)

The Dutch case builds on a sequence that started in late December 2025. The Netherlands Food and Consumer Product Safety Authority, or NVWA, reported that on December 24, 2025, it received a notification about two sick cats; one tested positive for avian influenza and died two days later. That tracing led investigators to a dairy farm in Noardeast-Fryslân, Friesland. Initial screening on January 15, 2026, found no active virus in milk samples, but one cow had antibodies indicating prior infection. Wageningen University & Research later said the cow had experienced mastitis and reduced milk production in mid-December, signs consistent with H5N1 infection, though no samples were collected during illness to confirm active infection at that time. (nvwa.nl)

What changed is that the Dutch story no longer appears limited to a single seropositive animal. Weese reported in February that five cows on the farm had now tested positive for H5N1 antibodies, strengthening the case that this was a real farm-level exposure event rather than a one-off false positive. That matters because Dutch authorities and WUR had already emphasized that no virus particles were found in the sampled cattle or milk, and that the situation was not comparable to the U.S. outbreak, where infected cows shed virus in milk. Still, WUR also noted that European H5N1 strains can infect bovine respiratory epithelial cells, and that milk splashing in the parlor could theoretically contribute to transmission if infected cows are shedding virus. (wormsandgermsblog.com)

The cat side of the story is just as important. Weese said the Washington case was believed to be associated with wild-bird exposure rather than contaminated food, a distinction worth noting after multiple raw food-linked feline H5N1 cases in the U.S. over the past year. International and U.S. guidance has increasingly stressed that cats are especially vulnerable to H5N1 through prey, raw poultry, and unpasteurized milk or dairy exposure. FDA guidance says cat and dog food manufacturers using uncooked or unpasteurized poultry or cattle ingredients must account for H5N1 in food safety plans, reflecting how firmly the raw-food risk has entered veterinary and regulatory thinking. (wormsandgermsblog.com)

Recent literature supports the concern that feline infections are both underrecognized and often severe. A 2025 systematic review in Open Forum Infectious Diseases identified 607 avian influenza infections in felines reported from 2004 to 2024 across 18 countries and found that the recent increase in domestic cat cases tracks the emergence of H5N1 clade 2.3.4.4b. The authors described an acute, often fatal disease pattern with respiratory and neurologic involvement, and suggested the apparent fatality rate may be inflated by detection bias because dead or severely ill cats are more likely to be tested than cats with mild infection. That aligns closely with Weese’s observation that milder feline cases may be missed. (academic.oup.com)

Why it matters: For veterinary professionals, these cases reinforce a practical surveillance lesson: unexplained illness or death in cats, especially outdoor cats, barn cats, or cats on dairies and poultry-adjacent properties, should trigger questions about H5N1 exposure and whether other animals on the premises need evaluation. The Dutch investigation is a strong example of cats functioning as sentinels for broader farm risk. It also suggests that if H5N1 reaches cattle in Europe, it may not always announce itself with dramatic herd-level illness. Mild mastitis, reduced production, or no obvious clinical signs at all could complicate detection. (wur.nl)

There’s also a One Health implication. WUR said the Dutch cow was not shedding virus when tested and that pasteurization mitigates food safety risk, but the appearance of antibodies in multiple cows still raises questions about how often brief or subclinical infections may be missed. For small animal and mixed-animal veterinarians, that means exposure history matters more than ever, including wild-bird contact, raw diets, raw milk access, and farm environment. It also means clinics may need lower thresholds for PPE, testing discussions, and coordination with animal and public health authorities when cats present with acute neurologic or respiratory disease in relevant exposure settings. (wur.nl)

What to watch: The next key signals are whether Dutch investigators publish the full serology from the affected herd, whether any viral sequencing or additional farm-to-farm surveillance data emerge, and whether more agencies formally position cats as early-warning indicators in H5N1 investigations on dairies and other mixed-species operations. (wur.nl)