Pasteurisation inactivates avian flu in milk, research confirms

In March 2024, dairy cows in Texas were found to be infected with highly pathogenic avian flu, or H5N1 bird flu, in the first known case of the virus spreading to cattle. Since then, H5N1 has been found in about 200 animals — and three people — across 12 states in the US, according to the Centers for Disease Control and Prevention.

Soon after the discovery in cattle, diagnostic testing revealed that an infectious form of the virus was present in raw milk, suggesting the virus passes from cow to milk. This led researchers to investigate whether dairy products pose a risk to consumers.

Testing nearly 300 milk products from 132 processors, Dr Erica Spackman, a virologist at the U.S. Department of Agriculture (USDA) in Athens, GA, and her collaborators found no infectious virus in the samples — the details have now been reported in the Journal of Virology, a journal of the American Society for Microbiology.

“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.”

The milk processing pipeline includes multiple layers of protection, Spackman said. Microbiological surveillance of milk products can identify pathogens, and milk from cows with mastitis or other disease conditions does not enter the food supply. Finally, heating during the pasteurisation process can destroy H5N1 and other more common bacterial pathogens.

The U.S. Food and Drug Administration and the USDA investigated whether pasteurisation effectively eliminated risks posed to consumers. Between 18 and 22 April 2024, researchers used real-time PCR to analyse 297 samples of pasteurised 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 said the new findings “give us reassurance that what we have been doing — pasteurisation — is keeping us safe from what we don’t know about.”

More on bird flu and Australian cases

Bird flu primarily infects and spreads among migratory birds and can be transmitted to domestic poultry, but the virus has been detected in other animals as well. Recently, other than the cattle mentioned above these have included cats, dogs and juvenile goats, as well as a polar bear in Alaska and elephant and fur seals in the Antarctic.

While there have been cases of bird flu on farms in Australia, including locations in western Victoria, New South Wales and Canberra, the H5N1 strain has not been detected in birds in Australia. There has only been one human case of avian influenza A(H5N1) reported in Victoria — the child acquired the infection while overseas and has now recovered.

According to Food Standards Australia New Zealand (FSANZ), bird flu (avian influenza) is not a food safety concern and it is safe to eat properly handled and cooked chicken meat, eggs and egg products. There is no evidence to show the virus can be transmitted to people through properly prepared food, FSANZ stated.

Image credit: iStock.com/ naturalbox