Widespread Bird Flu Infections Identified in Dairy Cows and Veterinarians, CDC Study Reveals

A recent study conducted by the U.S. Centers for Disease Control and Prevention (CDC) has revealed that the H5N1 bird flu virus may be circulating more widely among livestock than previously believed. This study also indicates that veterinarians could be unknowingly exposed to the virus.

Published in the CDC's Morbidity and Mortality Weekly Report, the research involved an analysis of blood samples from 150 veterinarians who specialize in bovine care across 46 states and Canada. The findings showed that three of these veterinarians tested positive for antibodies to the H5N1 virus. Notably, none of these individuals reported any symptoms commonly associated with the infection, such as conjunctivitis, which is frequently observed in human cases.

Interestingly, the three veterinarians who tested positive for the antibodies stated they had not worked with any cattle or poultry known to be infected with the virus. For instance, one veterinarian practiced exclusively in Georgia, dealing with dairy cows, and in South Carolina, where poultry is managed--all states that have yet to report any H5N1 infections.

Seema Lakdawala, a microbiologist at Emory University, expressed surprise at the low percentage of veterinarians (2%) testing positive for the antibodies, especially in light of another CDC study showing a 17% infection rate among dairy workers sampled. The unexpected results suggest that asymptomatic infections may go undiagnosed, highlighting the need for serum surveillance studies to better assess the risks to veterinarians and livestock workers. Lakdawala emphasized the importance of enhancing biosafety measures, including respiratory and eye protection, to mitigate exposure risks.

Jennifer Nuzzo, director of the Pandemic Center at Brown University, characterized the study as a mix of good and bad news. While it raises concerns about the possibility of unreported H5N1 outbreaks on farms, it is also reassuring that the infections among veterinarians are not widespread. This indicates that preventive measures can be improved to halt the virus's spread to more farms and workers.

The analysis took place in September 2024, during which only four human cases had been reported, and infections were believed to be limited to dairy cattle in 14 states. Since that time, the number of infected individuals has risen to 68, with 40 of those working closely with infected dairy cows. The virus has now been identified in herds across 16 states.

John Korslund, a retired USDA scientist, commented that while finding H5N1 antibodies in veterinarians is notable, it serves as an imprecise method for measuring the incidence of infections in cattle. He highlighted the significant risk that humans may be susceptible to subclinical infections, which could lead to the reassortment of the virus, a process where different strains mix and potentially create new, more virulent forms.

One strain of concern, known as D1.1, has been detected in dairy cattle in Nevada and in one human case in the state. Korslund warned that this evolving strain could alter the landscape of infection risks among both animals and humans.

In conclusion, the findings from this study underscore the necessity for ongoing monitoring and enhanced protective measures for those working in close contact with livestock to prevent further outbreaks of H5N1.