A Los Angeles County veterinary worker who treated a sick house cat has tested positive for antibodies to H5N1 bird flu, federal investigators report, marking the first serologic hint that a domestic cat may have passed the virus to a person. The worker never developed symptoms and initially had a negative PCR test, but later bloodwork turned up neutralizing antibodies. The case surfaced in the wake of a cluster of severely ill cats in Los Angeles that public health teams linked to commercially purchased raw milk and raw pet food.
Between November 2024 and January 2025, 19 domestic cats from five Los Angeles County households fell ill after consuming raw milk, raw meat, or raw pet food. Of the cats that were tested, nine were positive for influenza A(H5N1), and officials identified 139 people as potentially exposed. In April 2025, investigators invited those people to participate in antibody testing and collected blood samples from 25 volunteers. One asymptomatic veterinary professional, whose blood was drawn about 120 days after exposure, tested positive for neutralizing and hemagglutination-inhibition antibodies to two H5N1 clade variants, despite having a negative PCR test about a week after exposure. These results, investigators wrote, “provide evidence of zoonotic transmission of influenza A(H5N1) virus from domestic cats to humans,” according to CDC's MMWR.
What labs found on dairies
Follow-up sampling on multiple California dairy farms found infectious H5N1 virus in milking parlors, in milk, and in reclaimed farm wastewater. The findings suggest that unpasteurized milk and contaminated raw pet foods can carry infectious virus into homes and the broader food chain. Surveillance teams documented high viral loads in milk and evidence that aerosols and waste streams on farms could create additional exposure routes, prompting concern about downstream risks for pets and people, according to PLOS Biology.
Local response and recalls
In response, Los Angeles County public health officials urged residents not to feed pets raw diets and coordinated with state and federal partners after H5N1 turned up in some commercial raw pet products. Local coverage has followed a series of recalls and county advisories that tied several serious illnesses in strictly indoor cats to recalled products, as the Los Angeles Times reported.
Advice for pet owners and clinics
Investigators are urging pet owners to skip raw milk and other raw animal products for their cats, and they want veterinary staff to use eye protection, respiratory protection, and other PPE when handling animals that might be infected. Clinics are being asked to revisit infection-control protocols and promptly report suspected H5N1 cases to public health authorities to limit exposure, guidance summarized in CDC's MMWR.
National picture
The national situation summary from the CDC lists at least 71 human A(H5) cases in the United States since February 2024, including two deaths, with most infections linked to sick livestock or birds. The new cat-linked serologic finding adds household pets to the list of animal exposures that have preceded human infection and is one reason officials continue to monitor veterinarians, farm workers, and others who work closely with animals, per the CDC.
Bottom line for Angelenos
For most residents the immediate risk remains low, but this episode highlights how household pets and raw food products can create surprise exposure paths. Public health experts say veterinarians, pet owners, and dairy workers should stick to current guidance, use appropriate PPE when needed, and report suspicious animal illnesses quickly.
