Bird flu in cattle: 2nd type of strain detected in US dairy cows

A new type of bird flu has been detected in dairy cattle in Nevada, according to the U.S. Department of Agriculture – which noted how this strain is different from the version that has spread in U.S. herds since last year. 

Officials said this means distinct forms of the bird flu virus known as Type A H5N1 have spilled over from wild birds into cattle at least twice. 

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Here’s what to know:

Bird flu in cattle: Second type of strain found

What we know:

A version of the H5N1 bird flu virus known as B3.13 was confirmed in March after being introduced to cattle in late 2023, scientists said. It has infected more than 950 herds in 16 states. The new version, known as D1.1, was confirmed on Jan. 31 in Nevada cattle, according to the USDA. It was detected in milk collected as part of a surveillance program launched in December.

USDA officials said they would continue to work with the Nevada Department of Agriculture by conducting additional "on-farm investigation, testing, and gathering additional epidemiological information to better understand this detection and limit further disease spread."

What we don't know:

It’s unclear whether the spillover was a recent event or whether the new strain has been circulating for longer. Officials with the USDA’s Animal and Plant Health Inspection Service said they would post genetic sequences and other information about the new form of the virus to a public repository later this week for scientists to better understand that question. 

Why you should care:

At least 67 people in the U.S. have been infected with bird flu, mostly those who work closely with dairy or cattle, according to the U.S. Centers for Disease Control and Prevention.

Although bird flu viruses usually do not infect people, there have been some cases of human infection, which the CDC calls "rare." This can happen when the virus gets into a person's eyes, nose or mouth, or is inhaled as droplets in the air. 

The new D1.1 version of the virus was the type linked to the first U.S. death tied to bird flu and a severe illness in Canada, according to officials. A person in Louisiana died in January after developing severe respiratory symptoms following contact with wild and backyard birds. In British Columbia, a teen girl was hospitalized for months with a virus traced to poultry.

What they're saying:

Experts said the detection of the new strain raises more questions about wider spread and the difficulty of controlling infections in animals and the people who work closely with them.

"I always thought one bird-to-cow transmission was a very rare event. Seems that may not be the case," Richard Webby, an influenza expert at St. Jude Children’s Research Hospital, told the Associated Press. 

Angela Rasmussen, a virus expert at the University of Saskatchewan in Canada, who helped identify the first spillover, emphasized how the detection of the new strain underscores "why it's really important to test and continue testing."