In March 2024, dairy cows in Texas were found to be infected with highly pathogenic avian flu, also known as H5N1 bird flu, marking the first known case of the virus spreading to cattle. Since then, H5N1 has been found in about 200 animals and 3 people across 12 states, according to the Centers for Disease Control and Prevention. The virus was soon detected in raw milk, prompting researchers to investigate whether dairy products pose a consumer risk. Their findings are published this week in the Journal of Virology, a publication of the American Society for Microbiology.
“How far is the virus getting through?” asked Erica Spackman, Ph.D., a virologist at the U.S. Department of Agriculture (USDA) in Athens, Georgia. She and her collaborators tested nearly 300 milk products from 132 processors to find out.
The researchers found no infectious virus in the samples. “Milk is safe,” Spackman said. “Just like bacterial pathogens that occur in milk, or other viruses that could occur in milk, the sanitation processes that are in place are getting rid of the pathogens.”
According to Spackman, the milk processing pipeline has several layers of protection. Microbiological surveillance of milk products can identify pathogens. Milk from cows with mastitis or other diseases does not enter the food supply. Additionally, heating during the pasteurization process can destroy H5N1 and other common bacterial pathogens.
Bird flu primarily infects and spreads among migratory birds and can be transmitted to domestic poultry. However, the virus has been detected in other animals, such as cats, dogs, juvenile goats, a polar bear in Alaska, and elephants and fur seals in the Antarctic. The discovery of H5N1 on dairy farms in March was surprising, as the virus had never been found in dairy cattle before.
Following the discovery, diagnostic testing found an infectious form of the virus present in raw milk, suggesting that the virus passes from cow to milk. This finding led the U.S. Food and Drug Administration and USDA to investigate whether pasteurization effectively eliminated risks for consumers. Between April 18 and April 22, 2024, researchers used real-time PCR to analyze 297 samples of pasteurized retail milk products, including 23 types of products, collected from 17 states.
“We did a viability assay to detect live virus and went as sensitive as we could to get even the least little bit of virus, but couldn’t detect anything,” Spackman said. Using PCR, the researchers did identify viral genetic material in 20% of samples. “It looks like the virus is just totally inactivated,” she said.
“Spackman stated that the new findings provide reassurance that our pasteurization processes are effectively protecting us from unknown risks. The American Society for Microbiology is a prominent organization dedicated to the life sciences, comprising 32,000 scientists and health practitioners. ASM’s mission is to promote and advance the microbial sciences.”
