H5N1 mutation on Calif. dairies raises transmission concerns

The Los Angeles Times has reported a potentially troubling genetic mutation in dairy cows infected with H5N1 bird flu in San Bernardino County, but federal agencies have yet to confirm the findings.

The mutation, known as PB2 E627K, has previously been linked to increased mammal-to-mammal transmission and higher disease severity, raising concerns among scientists.

This development comes nearly a year after the first cases of bird flu were detected in Texas dairy cattle. While official confirmation from the U.S. Department of Agriculture and Centers for Disease Control is still pending, researchers have identified the mutation in four herds, believed to be in San Bernardino County, based on genetic data uploaded to the Global Initiative on Sharing Avian Influenza Data.

The mutation was first seen in a Texas dairy worker last March, who reported mild symptoms. However, lab studies using ferrets indicate the strain can be highly lethal.

Experts remain divided on the implications. Some, like Yoshihiro Kawaoka of the University of Wisconsin-Madison, emphasize that this mutation has shown the ability to spread between mammals in controlled studies. Others, like Richard Webby of St. Jude Children’s Research Hospital, cautioned that while the mutation alone may not be alarming, its continued spread in cows could increase the risk of human infections.

Since January 2022, highly pathogenic avian influenza (HPAI) A(H5) viruses, specifically H5N1 from clade 2.3.4.4, have been detected in wild birds, commercial poultry, and backyard flocks across the U.S. These are the first confirmed cases since 2016.

Currently, outbreaks have been reported in all 50 states, affecting 666 counties and totaling 1,641 outbreaks. The USDA’s Animal and Plant Health Inspection Service provides regularly updated data on affected locations, including state, county, outbreak date, flock type, and size. Recent outbreaks include cases in Nebraska, New York, Iowa, Indiana, Colorado, and Kansas, affecting commercial duck breeders, live bird markets, and non-poultry flocks.

Nearly 1,000 dairy herds have been infected with H5N1 since the outbreak began, with over 750 of them in California. So far, 70 human infections have been reported, and one person has died. Public health experts are urging increased monitoring of dairy workers, given the potential for the virus to evolve further.