The U.S. Centers for Disease Control and Prevention has confirmed what health officials describe as the first documented evidence of possible bird flu transmission from a domestic cat to a human, marking a significant development in the ongoing monitoring of H5N1 avian influenza in mammals. The finding emerged from a CDC-led investigation into a cluster of infected pet cats in Los Angeles County, California, between late 2024 and early 2025.
The case involved a veterinary professional who developed antibodies against the H5N1 virus after exposure to infected cats, despite never developing symptoms. According to the CDC, the findings do not suggest widespread cat-to-human transmission is occurring, and the agency continues to classify the overall public health risk as low. However, researchers say the case highlights how the virus is increasingly appearing in mammals — including pets — and reinforces concerns about the evolving behavior of H5N1.
The Investigation Began After Multiple Cats Became Critically Ill
According to the CDC’s Study published on May 7th in the agency’s Morbidity and Mortality Weekly Report (MMWR), Los Angeles County health officials investigated 19 domestic cats from five separate households that became severely ill between November 2024 and January 2025. The animals reportedly suffered respiratory, neurological, and liver-related symptoms after consuming commercially purchased raw milk, raw meat, or raw pet food products.
Of the 19 cats involved in the outbreak, 14 either died naturally or were euthanized because of the severity of their condition. Nine cats were formally tested, and every tested animal was confirmed positive for highly pathogenic avian influenza A(H5N1), specifically the clade 2.3.4.4b genotype B3.13 strain — the same strain that has circulated widely among birds and other mammals in the United States.
Health investigators later discovered that some of the raw food products consumed by the cats also tested positive for H5N1 contamination. Veterinary reports, laboratory testing, and epidemiological links between households helped officials trace the cluster and begin monitoring potentially exposed humans.
CDC Found Evidence Of Infection In One Veterinary Worker
As part of the public health investigation, Los Angeles County health officials identified 139 people who may have been exposed to the infected cats. Those individuals included pet owners, veterinary clinic employees, and animal control personnel involved in handling or treating the sick animals. All exposed individuals were monitored for symptoms over a 10-day period after exposure.
Although 30 people reported mild flu-like symptoms during monitoring, none initially tested positive through standard PCR testing. However, months later, health officials conducted a serologic survey — a blood antibody study — involving 25 exposed individuals. The testing revealed that one asymptomatic veterinary professional had antibodies specific to the H5N1 strain linked to the infected cats.
According to the CDC, the veterinary worker reported no other known exposure risks to H5N1, such as contact with infected poultry, dairy cattle, or wild birds. Investigators also noted that the individual did not consistently use respiratory or eye protection while treating the infected cats. While the CDC described the finding as “serologic evidence of possible transmission,” the agency emphasized that the worker never became visibly ill and tested PCR-negative shortly afterward.
Why Cats Have Become A Growing Concern In The Bird Flu Outbreak
Scientists have been closely monitoring cats during the H5N1 outbreak because felines appear unusually vulnerable to severe illness from the virus. Since 2022, the virus has increasingly spilled over from birds into mammals, including foxes, skunks, seals, dairy cattle, and domestic cats. The U.S. Department of Agriculture has documented numerous feline infections across multiple states.
Researchers believe cats may become infected after consuming contaminated raw meat or milk products, hunting infected birds, or being exposed to contaminated farm environments. Veterinary experts have repeatedly warned that raw pet food diets may pose an underrecognized risk during the current H5N1 outbreak.
Unlike dogs, which generally appear less susceptible to severe H5N1 disease, infected cats often develop rapidly worsening neurological and respiratory symptoms. Several veterinary researchers have described feline infections as particularly aggressive, with high mortality rates once symptoms appear. The CDC investigation has now intensified concerns because it demonstrates that close contact with infected cats may occasionally expose humans as well.
Health Officials Stress That The Public Risk Remains Low
Despite the historic nature of the finding, federal health agencies continue stressing that H5N1 does not currently spread easily between humans. The CDC states that most human H5N1 infections identified in the United States since 2024 have involved direct exposure to infected poultry or dairy cattle. As of the agency’s latest update, 71 human cases have been reported nationwide since February 2024.
The CDC also emphasized that the recent cat-associated case does not mean household pets are becoming major drivers of transmission. Instead, officials say the findings reinforce the importance of infection control practices in veterinary settings and highlight the risks associated with feeding pets unpasteurized milk or raw meat products.
Veterinary organizations, including the American Veterinary Medical Association, have urged veterinary staff to use appropriate personal protective equipment when handling animals suspected of carrying H5N1. The CDC also continues advising pet owners to prevent cats from consuming raw animal products and limit outdoor hunting exposure where possible.
Scientists Say The Case Highlights The Importance Of Vigilance
Public health experts say the significance of the case lies less in immediate danger and more in what it reveals about the evolving ecology of H5N1. The virus has now demonstrated the ability to infect an expanding list of mammal species, increasing opportunities for adaptation and mutation. Although sustained human-to-human spread has not been detected, scientists remain cautious because influenza viruses are known for their ability to evolve rapidly.
Researchers involved in the CDC investigation stressed that this appears to have been an isolated exposure involving prolonged close contact with infected cats under veterinary conditions. There is currently no evidence suggesting casual interaction with healthy household pets poses a meaningful threat to the general public.
Still, experts argue the case serves as an important reminder that diseases crossing between species often begin quietly. The increasing spread of H5N1 into mammals, including pets that live closely alongside humans, means surveillance and early detection remain essential.
Conclusion
The CDC’s confirmation of possible bird flu transmission from a domestic cat to a human marks a scientifically important moment in the ongoing H5N1 outbreak, even if the immediate public risk remains low. The infected veterinary worker never became sick, no wider chain of transmission was identified, and officials continue emphasizing that H5N1 is not spreading easily among people.
But the case also highlights how modern outbreaks are no longer confined to farms or wild bird populations alone. Pets, raw food supply chains, veterinary clinics, and household environments are increasingly becoming part of the broader conversation around zoonotic disease transmission. For now, health agencies are urging awareness rather than panic — especially among pet owners and veterinary professionals who work closely with animals every day.
