Silent Spread—Three Bovine Veterinarians Unknowingly Infected with H5N1
In the shadow of a growing H5N1 avian influenza outbreak among U.S. dairy cattle, a startling discovery has emerged: three bovine veterinarians were unknowingly infected with the virus. This revelation, uncovered through a recent serosurvey, underscores the silent spread of the disease and highlights the urgent need for systematic surveillance to protect those on the frontlines of animal care.
The H5N1 Outbreak: A Growing Crisis
Since its initial detection in March 2024, highly pathogenic avian influenza (HPAI) type A H5N1 has swept through U.S. dairy herds, infecting at least 968 herds across 16 states. The virus, which has also spilled over into wild birds, poultry, and even mammals, has now infected 68 people in the U.S., with cases linked to exposure to infected poultry, dairy cows, and other animals.
Amid this crisis, a serosurvey conducted in mid-September 2024 sought to understand the prevalence of H5N1 infections among bovine veterinarians—a group at high risk due to their close contact with cattle. The results, published in the Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report on February 13, 2025, revealed that three of 150 veterinarians tested had evidence of recent H5N1 infection.
The Silent Spread: Unseen Infections
What makes these findings particularly alarming is that none of the three veterinarians exhibited symptoms of H5N1 infection, such as respiratory issues, flu-like symptoms, or conjunctivitis. None had been tested for influenza since January 2024, and none had worked with dairy cattle confirmed or suspected to have H5N1 infections.
One of the veterinarians had worked with poultry confirmed to be infected with H5N1, while another practiced in multiple states, including those with known H5N1 infections in cattle. The third veterinarian, however, had only worked in Georgia and South Carolina—states with no reported H5N1 cases in cattle or humans—and reported no exposure to animals suspected of carrying the virus.
All three veterinarians reported wearing gloves or protective clothing when working with cattle, but none used respiratory or eye protection. This suggests that the virus may be spreading through less obvious routes, such as aerosolized particles or indirect contact with contaminated surfaces.
A Call for Systematic Surveillance
The study, a collaboration between the CDC, the American Association of Bovine Practitioners (AABP), and the Ohio Department of Health (ODH), highlights the need for enhanced surveillance among at-risk populations. “These data highlight the possible benefit of national seroprevalence assessments of recent HPAI A(H5) infection among practitioners at increased risk for exposure,” the study authors wrote. Such assessments could help identify undetected infections and inform hazard assessments in states without confirmed H5N1 cases.
The serosurvey involved 150 veterinarians who had worked with cattle in the previous three months. Participants, who practiced in 46 states and Canada, were asked about their exposure to various animal species, their use of personal protective equipment (PPE), and their thoughts on a potential H5N1 vaccine. Blood samples were collected to test for antibodies against the virus.
The Bigger Picture: A Virus on the Move
The H5N1 outbreak has continued to evolve since the serosurvey was conducted. Most human infections have been linked to the H5N1 clade 2.3.4.4b, genotype B3.13, but a new genotype, D1.1, has recently emerged. This genotype, identified in dairy cows and a dairy worker in Nevada, is now the dominant strain in North American wild birds and has spilled over into mammals and domestic poultry.
The U.S. Department of Agriculture (USDA) has emphasized the importance of rigorous biosecurity measures to curb the spread of H5N1. Financial assistance is available to herd owners for implementing enhanced biosecurity practices, and the USDA’s Animal and Plant Health Inspection Service (APHIS) is working closely with state partners on surveillance and control efforts.
What This Means for Veterinarians
For bovine veterinarians, the findings are a wake-up call. The silent spread of H5N1 underscores the importance of:
Enhanced PPE Use: While gloves and protective clothing are essential, respiratory and eye protection may be necessary to reduce the risk of infection.
Regular Testing: Veterinarians working with cattle, poultry, or other at-risk animals should consider regular testing for H5N1, even in the absence of symptoms.
Vaccination Advocacy: The development and distribution of an H5N1 vaccine for both animals and humans could play a critical role in controlling the outbreak.
Biosecurity Measures: Strict adherence to biosecurity protocols, including disinfection of equipment and limiting contact with potentially infected animals, is crucial.
A Path Forward
The discovery of asymptomatic H5N1 infections among veterinarians is a stark reminder of the virus’s ability to spread undetected. As the outbreak continues to expand, systematic surveillance, enhanced biosecurity, and increased awareness will be key to protecting both animal and human health.
For veterinarians on the frontlines, the message is clear: vigilance is essential. By staying informed, adopting rigorous safety measures, and advocating for systemic changes, the veterinary community can help curb the spread of H5N1 and safeguard the health of animals and humans alike.
For more information on H5N1 and biosecurity resources, visit the USDA and CDC websites.
