Veterinarians had undetected bird flu infections, but such cases are rare, CDC says
Key takeaways:
- Three bovine veterinarians had signs of prior bird flu infection without symptoms.
- The CDC said the results suggest that undetected infections are uncommon.
Three bovine veterinary practitioners had evidence prior infection with highly pathogenic H5N1 avian influenza despite having no apparent contact with infected cows, according to a study published in MMWR.
The results of the serosurvey of 150 bovine vets “suggest there could be U.S. states with A(H5)-positive people and animals that have not yet been identified,” the CDC wrote in a summary sent to reporters.
The findings also underscore the potential benefits of systematic surveillance for H5N1 in dairy cattle, milk and in humans who are exposed to cattle, the authors of the new report wrote.
“This survey represents a single point in time and aims to understand the spread of H5 infections among veterinary professionals who work with cattle,” the CDC told Healio.
“Like previous studies, this study underscores the potential for missed avian influenza A(H5) infections in people who work with animals, but the data suggest these undetected infections are uncommon.”
The CDC in December published data suggesting cases in humans were being missed because more people than previously thought had been exposed to and possibly infected with bird flu at dairy farms and while depopulating flocks where the virus had been detected.
Jerome Leonard, MD, MPH, of the CDC’s Epidemic Intelligence Service, and colleagues conducted the serosurvey in September 2024 among bovine veterinary practitioners at an annual conference who had been exposed to cattle in the previous 3 months.
Among the 150 participants, 143 practiced in the United States and 7 practiced in Canada. In all, 55% practiced in states with virus-positive dairy herds and 17% worked with cattle who were known or suspected to have been infected.
All participants were serologically tested for H5N1 antibodies, of whom three (2%; 95% CI = .7%-5.7%) had antibodies, suggesting that they had been infected with bird flu. All three veterinarians were based in the U.S. and none reported respiratory or influenza-like symptoms or conjunctivitis, according to the study.
Although all three veterinarians who tested positive had not worked with cattle known or suspected to be infected with bird flu, they all worked with multiple animals: all three worked with dairy cattle, two cared for nondairy cattle, one cared for poultry, and one worked at livestock markets. One veterinarian also worked with H5N1-positive poultry, according to the study.
In addition, all three veterinarians reported wearing gloves or some type of clothing cover when providing care to cattle, though none reported wearing respiratory or eye protection.
Forty-two states already participate in a national milk testing program, according to the USDA.
“Increased testing of herds and bulk milking tanks can help monitor for additional A(H5) positive herds and help better protect bovine veterinary practitioners and other animal workers,” the CDC said, also noting that “the current risk to the general public remains low.”
References:
- CDC. Avian influenza (bird flu): H5 bird flu: Current situation. https://www.cdc.gov/bird-flu/situation-summary/index.html. Updated Feb. 19, 2025. Accessed Feb. 19, 2025.
- Leonard J, et al. MMWR Morb Mortal Wkly Rep. 2024;doi:10.15585/mmwr.mm7404a2.
- USDA. Animal and Plant Health Inspection Service: National milk testing strategy. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/livestock/nmts. Updated Jan. 10, 2025. Accessed Feb. 19, 2025.
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