CHICAGO, April 3 (Reuters) - Migratory waterfowl are to

blame for widening avian-flu outbreaks in Texas cows and

poultry, and wild birds carrying the virus should be heading

north soon, state Agriculture Commissioner Sid Miller said on

Tuesday.

The U.S. government since last week has reported cases of

the disease in seven dairy herds in Texas and one person who had

contact with cows, making it the state most affected by the

country's first-ever outbreaks in cattle. Texas is the biggest

U.S. cattle producer.

The cases in dairy cattle and the second human case in two

years in the United States renewed 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

Cal-Maine to cull 1.6 million laying hens, the company

said on Tuesday. Texas had never before suffered such a major

outbreak at a commercial poultry facility, Miller said.

"This is spread by waterfowl," he said in an interview.

"It's migratory season."

The U.S. Department of Agriculture (USDA) first reported on

March 25 that a cow and milk from two dairies in Texas tested

positive for bird flu, with along milk from two dairies in

Kansas. The agency later confirmed positive tests in additional

dairy herds in Texas, New Mexico, Michigan and Idaho.

The strain of the virus found in the subsequent states is

very similar to the strain confirmed in the initial cases in

Texas and Kansas that appear to have been introduced by wild

birds, the USDA said.

"We're ready for the ducks to head north to their nesting

grounds," Miller said. "We think within a week or a little

longer they'll all be out of Texas and we'll be out of the

woods."

USDA said that transmission of the disease between cattle

cannot be ruled out.

The U.S. Centers for Disease Control and Prevention

considers the risk of bird flu for humans to be low. The Texas

patient's only symptom was eye inflammation, according to the

state's health department.

Richard Webby, a virologist at St. Jude Children's Research

Hospital in Memphis, said testing for flu in cattle is not

routine and that it was important to establish the connection

between the sickness in cows, and ducks and cats on the farms.

"Some smart people made the link and actually tested them

for flu," he said.

With these cases, people will start looking for similar

events in Europe and Asia, said Webby, director of the WHO

Collaborating Center for Studies on the Ecology of Influenza in

Animals and Birds.

The Texas outbreak may have started about a month ago when a

mysterious illness affected about 40% of the state's dairy

herds, Miller said. He said he now suspects it was bird flu,

though officials did not know it at the time and can't confirm

it because the animals recovered.

"We were testing for every cattle disease we could think of

and then somebody said, 'What are all these dead birds doing

around the dairies?'" Miller said.