Study Shows Human Sickness Risk From Bird Flu-Tainted Raw Milk; Virus Is Infectious In Unpasteurized Milk For Five Weeks

The Yomiuri Shimbun

12:20 JST, August 1, 2024

A study using mice suggests that consuming raw milk from cows infected with avian influenza poses an infection risk for humans.

According to a team of researchers from the University of Tokyo and other institutions, milk from cows infected with the H5N1 strain of bird flu contained high levels of the virus, and mice that were fed the milk subsequently became infected. The team’s work was published in the U.S. medical journal The New England Journal of Medicine on May 24.

In the United States, cows infected with the virus have been reported in nine states since March; some cases of infection in humans have also been confirmed.

The research team examined milk from infected cows in the United States and found that the milk contained over 10 million particles of the virus per milliliter. Mice to which the milk was administered showed viral multiplication in organs throughout their bodies.

The team heated one set of samples of the infected milk at 63C for 30 minutes and another set at 72C for 15 seconds. In both sets, the virus declined to less than 1/30,000 of its previous level. In unpasteurized milk from infected cows, the virus was found to remain infectious for five weeks, according to the team.

“Humans could be infected with avian influenza after consuming unpasteurized milk,” said Yoshihiro Kawaoka, director of the University of Tokyo Pandemic Preparedness, Infection, and Advanced Research Center.

“This is important information that all those concerned have been paying attention to,” said Yoshihiro Sakoda, professor of virology at Hokkaido University. “Pasteurized milk poses virtually no infection risk to consumers. But dairy farmers and people dealing with unpasteurized milk products need to take precautions.”