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A farm worker in Barron, Wis., is recovering after being infected with bird flu. The woman is the first person identified with the illness in that state, and Wisconsin public health officials are monitoring another 17 people who have been exposed.

In California, cows at 645 farms have tested positive for bird flu, and the dairy industry has been hit so hard in that state that California has declared a state of emergency.

But Minnesota epidemiologist Michael Osterholm called it a “wait-and-see situation.”

”Influenza viruses naturally occur in bird populations,” said Osterholm, the director of the University of Minnesota Center for Infectious Disease Research and Policy.

“That’s the origin for all the human viruses that we ultimately pick up ourselves. And what’s happened over the course of the past several years is a new strain of this bird flu virus — a particular type of H5N1 virus — has emerged in wild birds.”

He said of the 62 cases known about in humans, all but two have resulted in mild illness, and there is no evidence of human-to-human transmission.

”The case in Barron County is an example of a mildly ill individual,” he said. For now, the focus is on eliminating the virus in farm animals. “We’d surely like to see the virus out of the animal population that we interface with.”