Avian Influenza Virus Detected in Dairy Cows in Nevada

A version of the avian influenza virus different from the one affecting herds since last spring has been detected in dairy cows in Nevada, according to the USDA.

This finding raises questions about previous assumptions that the outbreak in dairy cows began with a single event when the virus jumped from birds to cows in the Texas panhandle last year. It suggests that cows may be more susceptible to H5N1 than previously understood, and that officials still lack clarity on how the virus is spreading among cows. This uncertainty could increase the risk for farmworkers and others in close contact with the animals.

"It increases the risk of severe disease to dairy farm workers infected with exposure to infected animals," said Seema Lakdawala, a virologist at Emory University. She added that this version of the virus might cause more severe disease.

This second version has predominantly affected wild birds and other mammals and has spread to poultry. It has been implicated in two severe human bird flu cases in North America: a Louisiana man who died in January, marking the first bird flu death in the United States, and a Canadian teen who was hospitalized for over two months and nearly died after exposure.

Most of the more than five dozen individuals infected with avian flu in the ongoing outbreak in the U.S. and Canada experienced mild symptoms and recovered quickly. They were infected with the same version of the virus found in over 950 dairy herds across 16 states, according to the USDA.

The discovery of a second version infecting cows surprised Richard Webby, an influenza expert at St. Jude Children's Research Hospital, who noted, "I thought the bird-to-dairy-cow transmission was an exceedingly rare event. This suggests that's not the case, and we might expect it to occur more regularly. It shows how little we understand about how the H5 virus is spreading."

While there does not seem to be an immediate change in human risk, which federal health officials have stated remains low for the general public, experts caution that more information is needed.

The Animal and Plant Health Inspection Service confirmed the detection of this virus variant on January 31, after it was found in raw milk collected from a silo as part of a national milk testing strategy initiated by the USDA last year. Lakdawala emphasized the need for enhanced testing of raw milk from dairy farms and processors to determine if this second version of the virus is present in cattle in other states, given its widespread presence among birds.