A California veterinary professional showed serologic evidence of H5N1 avian influenza infection after exposure to an ill cat, highlighting new risks for zoonotic transmission.
RT’s Three Key Takeaways:
- Zoonotic Transmission Evidence: Researchers identified serologic evidence of influenza A(H5N1) infection in an asymptomatic veterinary professional, suggesting possible transmission from a domestic cat to a human.
- Asymptomatic Infection Risk: The infected individual remained asymptomatic and initially tested negative via reverse transcription–polymerase chain reaction (RT-PCR), highlighting that some zoonotic infections may go undetected without serologic surveillance.
- Infection Control Necessity: The findings underscore the importance of using personal protective equipment and adhering to infection control practices when handling animals with respiratory, hepatic, or neurologic symptoms.
The CDC and the Los Angeles County Department of Public Health (LACDPH) identified serologic evidence of highly pathogenic avian influenza A(H5N1) in a veterinary professional, according to the CDC’s Morbidity and Mortality Weekly Report.
The case involves a veterinary professional who was occupationally exposed to an infected domestic cat in Los Angeles County between December 2024 and January 2025. This finding represents the first documented evidence of possible transmission of the H5N1 clade 2.3.4.4b virus from a domestic cat to a human.
“These findings provide evidence of zoonotic transmission of influenza A(H5N1) virus from domestic cats to humans,” the report stated.
The investigation began after 19 domestic cats in Los Angeles County became ill with severe respiratory, hepatic, or neurologic symptoms after consuming raw animal products, including raw milk and raw meat. Among the 139 individuals identified as having contact with the infected cats, 25 participated in a serosurvey.
The seropositive veterinary professional was asymptomatic throughout the exposure period and initially received a negative influenza A reverse transcription–polymerase chain reaction (RT-PCR) test result seven days after exposure. However, a blood specimen collected 120 days later showed antibodies specific to the H5N1 virus isolated from the infected cats.
The individual reported performing various clinical duties, including animal restraint, assisting with surgery, and performing airway procedures, without using respiratory or eye protection. The report noted that staff at the facility routinely wore gloves but no other personal protective equipment (PPE).
Public healthcare officials noted that the cats involved had consumed commercially purchased raw poultry or raw milk, which have been documented as sources of H5N1 infection in pets. The CDC advised pet owners to avoid feeding raw animal products to cats and urged veterinary professionals to maintain high vigilance.
The report also highlighted that the exposure occurred during a seasonal influenza A(H3N2) outbreak, which increases the risk for co-infection and potential reassortment between seasonal and avian viruses. Such events could lead to the emergence of novel viral strains with pandemic potential.
“Veterinary professionals should be aware of infection risks, use appropriate personal protective equipment, and adhere to recommended infection control practices to reduce the risk for zoonotic transmission of influenza A(H5N1),” the report authors stated.
