Study Finds Avian Influenza Exposure in Otherwise Healthy Veterinarians

Highly Pathogenic Avian Influenza (HPAI), also known as H5N1, has received significant media coverage recently, both from our team and many other experts closely monitoring this outbreak.  

The surveillance and depopulation of affected poultry flocks have been ongoing for the past couple of years, but have become increasingly common over the last few months as the virus spreads not only through the United States but also to other countries. According to the Centers for Disease Control and Prevention (CDC), there have been 69 confirmed human cases detected over the past year, identified either through national flu surveillance or targeted HPAI H5 surveillance.    

Infectious disease experts generally agree that H5N1 has high morbidity (the ability to cause illness) and high mortality (the ability to cause death), primarily in birds. However, some mammals, such as cats, appear more susceptible to this virus. Recent reports have linked the deaths of domestic cats to H5N1, which may be associated with uncooked diets or unpasteurized dairy products. Dairy cows also appear susceptible to H5N1, but only to the extent that the illness causes general symptoms such as decreased appetite and low milk production; however, the virus can be transmitted to other animals through unpasteurized milk from affected cows. 

Recently, the CDC published a surveillance study in collaboration with Ohio State University, the Ohio Department of Health, and the American Association of Bovine Practitioners (cattle veterinarians). Conducted in September 2024, the study involved 150 veterinarians who had worked with cattle in the previous three months and underwent blood draws to evaluate the presence of H5N1 antibodies through serology testing. This testing indicates whether a veterinarian has recently been exposed to the virus enough for their immune system to produce antibodies against it.   

As of September 2024, H5N1 had been detected in dairy cattle across 14 states. Among the 150 veterinarians who underwent serology testing for H5N1 antibodies, 82 practiced in states with H5N1-positive dairy herds, and 25 reported recently working with known or suspected dairy cattle infected with H5N1. Only three veterinarians tested positive for H5N1 antibodies, and none reported ever experiencing influenza or symptoms consistent with clinical influenza.  

 Of the three veterinarians who tested positive via serology, all worked with dairy cattle; however, none had worked with cattle confirmed to be positive for H5N1 or showing clinical symptoms associated with H5N1 infection. One of these veterinarians reported contact with H5N1-positive poultry. Two veterinarians stated they practiced in states where H5N1 cases in dairy cows had been documented, but one did not practice in a state with reported H5N1 in dairy cattle at the time of the survey. All veterinarians indicated that they wore protective rubber or latex gloves and sleeves while handling and working with dairy cattle, but they did not report using respiratory or eye protection during treatment and handling. 

So, What Does This Actually Mean? 

Although this is a relatively small sample size of veterinarians who had a higher chance of exposure to the H5N1 virus than most individuals, this study suggests that generally healthy humans are still at a low risk of illness when exposed to H5N1.   

This aligns with the virus's historical context. A study published in October 2024 stated that since 1997, there have been approximately 900 documented cases of H5N1 in people globally; however, the mortality rate among these individuals was close to 50%. This relatively high mortality rate, coupled with a comparatively low morbidity rate, is most likely due to predisposing health risks for those who died.   

Another key takeaway from the survey of veterinarian antibody presence is that it is highly likely that more veterinarians than the three from this group of 150 had exposure to H5N1 without sero-converting (producing antibodies against the virus), indicating a low potential for morbidity from this virus in humans at this time. This study also suggests that H5N1 may be more widespread than we initially thought, as it identified an individual veterinarian who had antibodies to H5N1 while in a state with no known cases in dairy cows at that time. 

Ultimately, H5N1 currently poses a low risk for causing illness in healthy individuals, even among those who routinely interact with infected animals. However, strict sanitation and conservative handling practices for poultry and dairy sources of H5N1 are key for veterinarians and others closely working in these sectors. The development of accurate, rapid, and affordable testing capabilities for all potential sources of exposure to animals and people will be one of the key methods to help ensure that the poultry and dairy industries possess the necessary tools to protect individuals associated with these sectors.  

The veterinary and food safety experts at BSM Partners are eager to answer any questions you or your customers may have about H5N1 and to assist your company in identifying the appropriate testing facility and protocols tailored to your specific needs. 

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About the Author

Dr. Bradley Quest, DVM, is the Principal Veterinarian at BSM Partners. He has practiced clinical veterinary medicine, developed and tested hundreds of pet food and health products, performs extensive animal health research, and helps navigate pet food ingredient approval for clients.