Madison Reporter

Researchers at the University of Wisconsin–Madison are leading efforts to monitor avian influenza in dairy milk, following the emergence of H5N1 avian influenza in dairy cattle in early 2024. The spread of the virus into cattle raised concerns about herd health, risks to dairy workers, and the potential for consumer infection through milk and other dairy products.

A team led by virologists at UW–Madison’s Influenza Research Institute began investigating these issues with support from the National Institutes of Health and the U.S. Department of Agriculture. Their work has informed policymakers as they address ongoing threats to agriculture and public health.

In May 2024, research published in the New England Journal of Medicine showed that raw milk containing H5N1 can infect mammals. However, according to Yoshihiro Kawaoka, professor of pathobiological sciences and leader of the group, heat treatment methods similar to pasteurization are highly effective at neutralizing the virus. This demonstrated that pasteurized dairy products are safe for consumption, while raw milk remains a risk for H5N1 infection.

Subsequent experiments revealed that ferrets infected with H5N1 through raw milk generally did not transmit the virus to other animals via airborne routes. Since ferrets are commonly used as models for human influenza transmission, this finding suggests that while people exposed to raw milk may contract H5N1, broader community spread is unlikely under current conditions. These results were reported in Nature in July 2024.

The researchers also studied a strain of H5N1 isolated from an infected dairy worker in Texas. They found this strain was lethal in ferrets even at low doses but noted it is no longer circulating in nature. The team continues to investigate why this strain caused only mild illness in humans but severe disease in other mammals.

Federal funding continues to support UW–Madison’s research as H5N1 remains a concern for farms and public health officials. The findings have provided guidance for public health authorities, farmers, and consumers regarding operational decisions and food safety.

"First, in a set of experiments the team described in the New England Journal of Medicine in May 2024, the researchers demonstrated that raw milk containing H5N1 poses an infection risk to mammals. However, the group, led by Yoshihiro Kawaoka, professor of pathobiological sciences, also found that heat treatment methods roughly similar to pasteurization, are highly effective at inactivating the virus. The experiments were crucial in demonstrating that pasteurized dairy products are safe, while raw milk and products made from it pose an H5N1 infection risk in people."

"Building on these experiments, Kawaoka and his team next showed that while raw milk is risky, ferrets that became infected by the virus for the most part did not spread H5N1 to other animals through the air. Ferrets are an established animal model for studying how influenza viruses might act in humans, so the findings represented relatively good public health news. Namely, while people exposed to raw milk either through their work on dairy farms or by consuming raw milk products are at risk of catching H5N1, the virus — or at least a primary circulating on dairy farms at the time — was unlikely to easily spread beyond those initial infections. Those findings were reported in the journal Nature in July 2024."

"Most recently, the team was able to study a strain of H5N1 isolated from an infected dairy worker in Texas. Although they found that this strain was 100% lethal in ferrets with only 10 infectious virus particles — a concerning finding — the UW–Madison researchers noted that it is no longer circulating in nature and are working to better understand why a strain that caused a relatively mild infection in a dairy worker would be so deadly in other mammals."

"The federally supported research is continuing as H5N1 remains a risk to farms and public health. The ongoing research has provided public health officials, farmers and consumers with actionable insights so they can make informed decisions about how to run their operations and what to eat."