Dairy Cow Specialist Veterinarian Shares Insights on Avian Influenza

In March 2024, the United States recorded its first instance of highly pathogenic avian influenza (HPAI) H5N1 spreading from birds to cattle. Experts suggest that the initial transmission occurred in the Texas Panhandle one to two months earlier before spreading to dairy farms in other regions through cattle movement.

 

According to the Centers for Disease Control and Prevention (CDC), dairy cows in 17 states have tested positive, affecting over 970 herds. Additional transmission events have been confirmed in Colorado and Arizona.

To date, 70 human cases of HPAI infection have been reported, with at least 40 linked to direct contact with dairy cattle. Most other cases have been associated with poultry farm exposure. The Louisiana Department of Health confirmed one fatality from avian influenza following exposure to wild birds and a backyard flock. 

However, no deaths have been linked to infections acquired from dairy cattle. The CDC also reported that since 2022, more than 200 mammal species, including seals, bears, and cats, have been affected by HPAI. 

In December 2024, a possible human case was investigated in a California child who had consumed raw milk, but follow-up testing was negative. While pasteurization eliminates the virus, raw milk remains a potential risk for transmission.

Dr. David Hernke, an assistant clinical professor at Tufts University’s Cummings School of Veterinary Medicine, specializes in dairy cow health and production medicine. He noted that the avian influenza outbreak is particularly concerning because it has adapted to a new host species and is actively spreading. 

According to Hernke, the American Association of Bovine Practitioners (AABP) provides regular updates on the outbreak, confirming that only three crossover events—from birds to cattle in Texas, Colorado, and Arizona—have led to all current dairy cow cases. Once infected, the virus spreads within herds rather than through direct bird-to-cow transmission.

One of the most unusual aspects of this outbreak is the virus’s ability to target the udder, resulting in significant shedding through milk. Testing for HPAI in dairy cattle primarily involves analyzing milk samples, as they provide the most accurate detection compared to nasal swabs. 

The virus’s presence in milk parlors and on dairy equipment increases the risk of transmission to other animals and potentially humans. Notably, veterinarians observed multiple cat deaths at affected dairies, and laboratory testing confirmed high concentrations of the virus in the deceased cats, likely due to consuming contaminated milk.