Assessing avian influenza in dairy milk

NIH

Certain influenza viruses are found in wild and domestic birds, earning the disease they cause the name “bird flu.” Over the last two decades, about 900 people have been infected with an avian influenza virus called H5N1. Most of them have had close contact with infected birds.

Past H5N1 strains have proven deadly for people, killing about half of those they’ve infected. However, to date, these H5N1 viruses haven’t spread effectively from person to person, limiting their potential to cause a pandemic.

In the past few years, a highly pathogenic avian H5N1, called HPAI H5N1, has spread from birds to infect more than 50 other animal species, including many kinds of mammals. In late March of this year, the first outbreak of HPAI H5N1 virus in dairy cows in the U.S. was reported. Three infections of people working with dairy cows have been picked up by virus surveillance methods. So far, symptoms have been mild.

HPAI H5N1 hasn’t yet gained the ability to spread directly between people. But researchers are concerned that infections could happen through the consumption of raw milk. Dairy milk purchased in the grocery store has been pasteurized—heated to a level high enough and long enough to kill most viruses or bacteria in the milk. However, 30 states in the U.S. allow the sale of raw dairy milk in some form.

In a new NIH-funded study, researchers from the University of Wisconsin-Madison, Wisconsin Veterinary Diagnostic Laboratory, and Texas A&M Veterinary Medical Diagnostic Laboratory used mice to test whether HPAI H5N1 found in raw milk can cause infections. Results were published on May 24, 2024, in the New England Journal of Medicine.