H5N1 cases in a Washington cat and Dutch cows widen concern

CURRENT FULL VERSION: A fatal H5N1 infection in an outdoor cat in Washington state and new antibody findings in Dutch dairy cows are adding to evidence that avian influenza surveillance can’t stop with birds. In Washington, state reporting described a Grant County cat that died after testing positive for H5N1 following exposure to a dead wild bird. In the Netherlands, investigators tracing a separate cat infection on a Friesland dairy farm found prior H5N1 infection in cattle on the premises, first in one cow and then, according to a later update cited by Scott Weese, in five cows. (reddit.com)

The Dutch case began with sick cats reported to authorities on December 24, 2025. The Netherlands later said one cat tested positive for avian influenza and died two days later, prompting source and contact tracing that linked the animal to a dairy farm. Initial testing of 20 cows and bulk tank milk found no active virus by PCR, but one cow had H5N1 antibodies, indicating past infection. That cow reportedly had mastitis and reduced milk production in mid-December, then recovered. Dutch officials said the milk from that clinically affected cow did not enter the human food chain, and milk from the farm was restricted to pasteurized products while the investigation was underway. (rijksoverheid.nl)

That finding mattered on its own because Wageningen University described it as the first detection of avian influenza antibodies in a cow in Europe. Researchers there also said experimental and in vitro work suggests the European H5N1 virus can infect bovine respiratory epithelial cells, making bovine susceptibility biologically plausible. Weese’s February update pushed the story further, reporting that five cows on the farm had now tested positive for H5N1 antibodies. He argued that five positives make a false signal less likely and raise the possibility of limited cow-to-cow spread, rather than multiple separate bird-to-cow events. That’s an inference, not a confirmed transmission chain, but it aligns with what has already been observed on US dairy farms. (wur.nl)

The cat side of the story is equally important. The European Centre for Disease Prevention and Control said the Dutch cat isolate, collected December 24, 2025, belonged to clade 2.3.4.4b, genotype EA-2024-DI, and clustered with bird strains detected in Europe in 2025. The agency also noted the isolate carried the PB2 E627K substitution, a mammalian-adaptation marker associated with replication in mammals. In Washington, state veterinary guidance issued in 2025 had already warned companion-animal veterinarians that cats are susceptible to H5N1 and that exposures may come not just from wild birds, but also from infected raw animal products such as raw pet food and raw milk. (ecdc.europa.eu)

Outside experts have been urging the profession to pay closer attention to feline H5N1 for months. A 2025 systematic review in Open Forum Infectious Diseases identified 607 avian influenza infections in felines across 18 countries from 2004 to 2024, with domestic cats accounting for 62.6% of cases and 71.3% of PCR-confirmed infections proving fatal. International Cat Care, responding to that review, said feline avian influenza reports, especially H5N1, have increased markedly since 2023 as the virus has expanded in birds and mammals, with cases reported most often in Asia, followed by Europe and North America. The group highlighted that common clinical signs include respiratory distress, neurologic disease, and even blindness, while some cats may be infected without obvious illness. It also emphasized that most reported feline infections appear to be bird-to-cat events, often after eating dead birds or contaminated raw chicken, but that raw, untreated milk from infected cattle has also been implicated. (academic.oup.com)

That broader feline picture matters because it sharpens both clinical suspicion and public-health relevance. International Cat Care noted that feline-to-human transmission has been discussed in connection with earlier outbreaks in tigers in Thailand and in a New York cat shelter where human infection was linked to sick felines. Those events do not mean cats are a common source of human infection, but they reinforce why barn cats, outdoor cats, and cats with raw-food or raw-milk exposure deserve careful attention as possible sentinels and, in some settings, bridging hosts at the animal-human interface. CIDRAP’s coverage of the review similarly highlighted calls for stronger surveillance in higher-risk cat populations, including dairy barn cats. (academic.oup.com)

Why it matters: For veterinary teams, these updates sharpen the case for exposure-based triage. Cats with acute neurologic disease, respiratory signs, sudden death, or a history of contact with dead birds, raw poultry diets, unpasteurized milk, or dairy environments should put H5N1 on the differential. On the production side, the Dutch findings are a reminder that cattle infections may be missed if surveillance relies only on active-virus detection, especially when animals are sampled after clinical recovery. Serology, milk monitoring, and careful review of recent mastitis or milk-drop events may be increasingly important tools, particularly if Europe begins to see more spillover into ruminants. (wur.nl)

For pet parents, the practical advice is becoming more consistent across jurisdictions: keep cats away from wild birds, avoid feeding raw poultry or unpasteurized milk, and seek veterinary evaluation quickly if exposed cats develop neurologic or respiratory signs. International Cat Care also specifically advised preventing farm cats from consuming on-farm milk and reducing bird predation where possible, including prompt safe disposal of dead birds. Public health agencies in the Netherlands said the animal-to-human risk from the circulating European H5N1 strain remains very low, but low risk isn’t the same as no risk when mammalian infections are broadening. (rijksoverheid.nl)

What to watch: The next signal will be whether additional European herds show serologic evidence of past H5N1 infection, and whether Washington or other US states publish more detail on recent feline cases, including exposure routes, sequencing, and any changes to testing recommendations. Just as important will be whether veterinary guidance becomes more explicit about managing higher-risk cats, especially barn cats and outdoor cats with access to birds, raw diets, or raw milk. (wur.nl)