Health officials are waiting this week to learn whether two people in southern Maine have been infected with West Nile virus.

No confirmation is expected before Friday.

Blood tests done on the two people were sent to the Centers for Disease Control and Prevention in Atlanta and on to a CDC lab in Colorado for analysis.

“We’re clearly evaluating (the) cases right now,” said Dr. Stephen Sears, the state epidemiologist. “But these may turn out to be nothing. We need far more information before we’ll know.”

West Nile virus and eastern equine encephalitis are transmitted through the bite of an infected mosquito. Some birds — including songbirds and crows — can carry the viruses, spreading them into the mosquito population and, in turn, to other birds, some mammals and humans.

One mosquito surveillance pool in York County tested positive for West Nile virus last week, but no human cases have been diagnosed in the state.

“It’s a matter of concern,” Sears said. “We have identified it. We now know it’s here.”

State officials are urging residents to “be aware and use mosquito precautions.” Generally, that means using some type of mosquito repellent and staying indoors from dusk to dawn, when mosquitoes are most active.

“We Mainers take mosquitoes for granted,” Sears said, but the appearance of West Nile virus in the state should be a signal to take responsible — but not fearful — precautions.

“One thing we do want to encourage people to do, is that if they see dead birds, to let us know,” said Anne Lictenwalner, director of the Animal Health Lab at the University of Maine. “We can test them.”

West Nile virus has struck “pretty heavily in New Hampshire and Massachusetts,” said Sears. “And there has been some eastern equine encephalitis in the Canadian provinces in the past,” so Maine continues to test routinely for the two diseases.

Sears said he knows of no pesticide spraying programs in Maine to date. He said any decision to do so would be made on the local level.

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