New tests confirm milk from flu-infected cows can make other animals sick —xa0and raise questions about flash pasteurization

New lab experiments with milk from cows infected by H5N1 influenza, known as bird flu, confirm that it is infectious, especially when left raw, or untreated, and potentially even when flash pasteurized.

The researchers, from a university’s School of Veterinary Medicine, are part of a federally funded program called the Centers of Excellence for Influenza Research and Response, or CEIRR. This network has been conducting rapid research to answer pressing questions in the H5N1 outbreak in dairy cattle.

In a research letter posted online, the researchers describe the results of experiments using milk from infected cows. They confirmed that raw milk was filled with H5N1 virus, and storing it at refrigerator temperature didn’t significantly decrease the viral levels over time.

The researchers also tested different types of pasteurization methods and found that vat pasteurization reduced the virus to undetectable levels. Flash pasteurization greatly reduced the virus but didn’t completely inactivate it.

Tests showed that milk samples heated through flash pasteurization were still able to infect incubated chicken eggs, indicating the virus remained infectious.

The researchers emphasized that their laboratory study conditions weren’t identical to large-scale industrial treatment of raw milk. Experts suggest that commercial flash pasteurization should include all necessary procedures to ensure full inactivation of the virus.

Recent FDA tests found traces of H5N1 genetic material in about 1 in 5 milk samples, but the viral fragments were inert and wouldn’t cause illness. The CDC advises against consuming raw milk or products made from it.

Research on mice demonstrated that the raw milk could infect them, suggesting a potential risk to humans. Officials from the US Department of Agriculture stated that raw milk from farms known to have H5N1 infections isn’t being sold to consumers.

Experts warn that raw milk is unsafe and consuming it won’t protect against H5N1 infection. Testing all cows and avoiding raw milk are safer alternatives.

The appearance of raw milk doesn’t necessarily indicate its safety, as filtering processes may remove debris. It is impossible to determine the safety of milk by its appearance alone.