Texas Agriculture Commissioner Sid Miller said migratory waterfowl are to blame for the expansion of avian influenza outbreaks in cattle and poultry in Texas, and wild birds carrying the virus will soon be migrating north.

Since last week, the U.S. government has reported cases of the disease on seven Texas dairy farms and one person who had contact with the cows, making it the worst-affected state in the country’s first cattle outbreak . Texas is the largest cattle producer in the United States.

The U.S. cow case and the second human case in two years have reignited concerns about the virus, which has been infecting poultry flocks and a growing number of other species globally since 2022.

A positive test at a Texas egg farm led egg producer Carle-Maine to cull 1.6 million laying hens, the company said Tuesday. Miller said commercial poultry facilities in Texas have never suffered an outbreak of this magnitude before.

“This is spread by waterfowl,” he said in an interview. “We’re ready for ducks to head north to their nesting grounds.”

The U.S. Department of Agriculture (USDA) first reported on March 25 that a cow and milk from two dairies in Texas and milk from two dairies in Kansas tested positive for avian influenza. The agency later confirmed cases at other dairy farms in Texas, New Mexico, Michigan and Idaho.

The U.S. Department of Agriculture said virus strains subsequently identified in states were very similar to those identified in the initial cases in Texas and Kansas and appeared to have been introduced by wild birds.

Experts say feces or other materials from infected wild birds may have contaminated feed or water sources consumed by dairy cows, although this has not been confirmed.

The USDA said it cannot rule out the possibility of the disease spreading among cattle. In Michigan, the herd that tested positive recently received cows from Texas, according to the agency.

After the outbreak, Mexico, a major market for U.S. beef and dairy products, said it was increasing monitoring and inspection of U.S. livestock imports.

The USDA said in an email that avian influenza primarily affects older cows on infected dairy farms, with “only a small percentage of each herd showing clinical signs.” The agency added that it has not received reports of clinical symptoms in beef cattle or of samples from beef cattle being tested for avian influenza.

“Why dairy cows and not beef cattle? Everyone is scratching their heads,” said Michael Kleinhenz, a veterinarian and clinical associate professor of dairy health at Texas A&M University.

“In the Texas Panhandle, we have dairy farms right next to feedlots and the cows are very close to pasture, but we’ve only seen this on dairy farms,” ​​Kleinhenz said.

“Dead birds around the dairy farm”

The U.S. Centers for Disease Control and Prevention considers the risk of human infection from avian influenza to be low. The patient’s only symptom was eye inflammation, according to the Texas Department of Health.

President Joe Biden has been informed of the avian flu situation, White House spokesperson Karine Jean-Pierre told reporters at a press briefing on Wednesday (local time).

Richard Webby, a virologist at St. Jude Children’s Research Hospital in Memphis, said testing cattle for influenza is not routine and it is important to establish links between the illnesses in cattle, ducks and cats.

“Some smart people discovered the link and actually tested them for influenza,” said Webby, director of the World Health Organization’s Collaborating Center for Ecological Research on Animal and Avian Influenza.

Miller said the Texas outbreak likely began about a month ago, when a mysterious disease affected about 40% of the state’s dairy herd. He said he now suspected it was bird flu, although officials didn’t know about it at the time and couldn’t confirm it because the animals had recovered.

“We were testing for every cattle disease we could think of, and then someone asked, ‘What are these dead birds doing around the dairy farm?’” Miller said.