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At least one person in Texas has been diagnosed with bird flu after having contact with dairy cows presumed to be infected, state officials said on Monday.

The announcement adds a worrying dimension to an outbreak that has affected millions of birds and sea mammals worldwide and, most recently, cows in the United States.

So far, there are no signs that the virus has evolved in ways that would help it spread more easily among people, federal officials have said.

The patient worked directly with sick dairy cows, said Lara M. Anton, a spokeswoman for the Texas Department of State Health Services. “We have tested around a dozen symptomatic people who work at dairies, and only the one person has tested positive” for the virus, she said in an email.

The patient’s primary symptom was conjunctivitis; the individual is being treated with an antiviral drug and is recovering, according to the Centers for Disease Control and Prevention.

The Department of Agriculture announced the first cases in dairy cows last week. As of Monday night, the virus had been confirmed in 11 herds across four states: Texas, Kansas, Michigan and New Mexico, the agency said. Cows in Idaho may also be infected.