US health investigators have reported the first serologic evidence of possible influenza A(H5N1) transmission from a domestic cat to a veterinary professional, adding an important new dimension to bird-flu surveillance in companion animals.
The finding comes from an investigation by the US Centers for Disease Control and Prevention (CDC) and the Los Angeles County Department of Public Health into a cluster of severely ill cats seen between November 2024 and January 2025.
The veterinary professional never developed symptoms and initially tested negative for active influenza infection. Months later, blood testing detected H5N1-specific antibodies, indicating that an infection had likely occurred after occupational exposure to an infected cat.
CDC investigators describe the case as evidence of possible cat-to-human transmission, rather than proof of sustained spread. The agency continues to assess the overall risk from H5 bird flu to the general public as low.
Nineteen cats became ill after consuming raw products
The investigation began after 19 domestic cats from five Los Angeles County households developed severe illness.
Owners reported feeding the cats commercially purchased raw milk, raw poultry, raw meat or raw pet food before illness began. Some of the implicated products had also tested positive for H5N1.
Nine cats were tested and all nine were positive for influenza A(H5N1) clade 2.3.4.4b, genotype B3.13.
The consequences for the animals were severe. Fourteen of the 19 cats died or were euthanized, with reported illness including respiratory, hepatic and neurological signs.
Fourteen cats were evaluated at 10 veterinary practices, meaning a substantial number of professionals came into close contact with infected or potentially infected animals before the public-health risk was fully understood.
Public health teams tracked 139 exposed people
Investigators identified 139 people with potential exposure to the affected cats.
The group included 126 staff members from 10 veterinary practices, 11 household members, one animal-control worker and one local public-health employee.
All were monitored for symptoms for 10 days after their last known exposure.
Thirty people reported influenza-like symptoms including cough, sore throat, runny nose, fatigue, muscle aches, headache and sneezing.
A total of 33 people underwent RT-PCR testing, including 18 symptomatic veterinary workers, 14 asymptomatic veterinary professionals and one asymptomatic pet owner.
None tested positive for H5N1.
April serology changed the investigation
The key discovery came several months later.
In April 2025, the CDC and Los Angeles County invited all 139 exposed individuals to participate in a serological survey designed to detect evidence of previous H5N1 infection.
Only 25 people participated, equivalent to about 18% of the exposure group.
Among them, one asymptomatic veterinary professional had antibodies against H5N1 viruses antigenically similar to the virus found in the cats.
The worker had been exposed in early December 2024 to an infected indoor cat that later tested positive for H5N1. The cat developed respiratory problems, neurological abnormalities and serious eye disease after consuming a commercial raw poultry-based pet food.
The veterinary professional had received a negative influenza test seven days after exposure and never reported illness.
Investigators also found no other recognised H5N1 risk factors. The worker reported no exposure to backyard poultry, wild birds or dairy cattle and no consumption of raw meat or raw dairy products.
Staff at the veterinary facility routinely used gloves but did not consistently wear respiratory or eye protection during examinations.
Taken together, the exposure history and antibody findings led researchers to describe the case as serologic evidence of likely occupational infection and possible transmission from the cat.
Why the earlier PCR test may have missed the infection
The finding also demonstrates the value of serology. RT-PCR looks for viral genetic material during active infection, while serology detects antibodies produced after exposure.
In this case, the veterinary professional’s later antibody result revealed evidence of an infection that would otherwise have remained undetected.
The investigators also acknowledged important limitations. Only 25 of 139 exposed people participated in the serosurvey, and paired acute and convalescent blood samples were not available.
That is why the CDC report uses careful wording around possible transmission rather than presenting the case as definitive proof of a broader cat-to-human transmission pattern.
Raw milk and raw pet food remain a major concern
The feline outbreak reinforces public-health warnings about feeding cats raw animal products.
CDC guidance advises owners to avoid giving cats raw milk, raw meat or raw pet food, all of which have been linked to H5N1 infections in companion animals.
Cats can develop severe disease after infection, including fever, loss of appetite, lethargy, eye and nasal discharge, breathing problems and neurological signs such as tremors, seizures, poor coordination or blindness.
Separate CDC-published research in 2026 has also detected H5N1 antibodies in domestic cats living close to dairy farms in California’s Central Valley, strengthening evidence that cats can be exposed in environments where the virus is circulating.
Veterinary clinics need stronger infection-control awareness
For veterinarians, the message is not that every cat with respiratory or neurological illness should be treated as an H5N1 case.
Instead, the CDC recommends considering bird flu when clinical signs are compatible and there is a relevant exposure history, including consumption of raw animal products or contact with infected birds, livestock or contaminated environments.
When H5N1 is suspected or confirmed, veterinary professionals should use appropriate personal protective equipment and minimise unnecessary close contact.
Respiratory and eye protection are especially important because influenza viruses can potentially enter through the nose, mouth or eyes during exposure to infected animals or contaminated secretions.
The Los Angeles case demonstrates why these precautions matter even before a laboratory diagnosis is confirmed.
Public risk remains low, but the veterinary finding matters
The investigation does not suggest that H5N1 is spreading efficiently from cats to humans.
CDC surveillance continues to report no evidence of sustained person-to-person spread, and the current risk to the general public remains low. People with close, prolonged or unprotected exposure to infected animals face greater risk.
What this case changes is the evidence surrounding companion animals.
Cats live in close contact with people, are routinely handled by veterinary professionals and can become infected through raw diets or exposure to infected wildlife and livestock environments.
For pet parents, the practical advice is straightforward: avoid raw animal products and seek veterinary care if a cat develops sudden respiratory, neurological or severe eye-related symptoms.
For veterinary teams, the case reinforces the need for consistent infection-control practices and a higher index of suspicion when exposure history points toward H5N1.
And for public-health agencies, it demonstrates why a One Health approach connecting animal health, human health and laboratory surveillance is critical for detecting infections that might otherwise remain invisible.
Pets News Network is India’s first dedicated media platform for the pet and animal industry. For breaking global pet news, brand coverage, and advertising enquiries, contact: info@petsnewsnetwork.com
