PROSSER, Wash. -- A Lower Valley resident may be the first human case of West Nile virus in the state this year.

A woman who lives in the Prosser area has tested with a presumptive positive for the virus, spread by mosquitoes, at a local laboratory.

The Benton-Franklin Health Department sent the tests to the state Department of Health for confirmation. Results will take a couple days, said Dr. Larry Jecha, health officer for Benton and Franklin counties.

The woman went to a local emergency room with encephalitus, a common illness often caused by West Nile, Jecha said.

She was treated and released and her condition is improving, Jecha added.

Jecha would not reveal the woman's age or if she lives near horses.

West Nile is transferred by mosquitoes and typically infects birds and horses.

So far this year, the virus has shown up in six birds, three horses and more than 160 mosquito samples in the state, most of them in Benton and Yakima counties. Jecha said a human case was only a matter of time.

"It's not unexpected," Jecha said.

Last year, health officials said three Washington residents may have been infected with the disease. One of them was a Yakima County woman who lives in the Lower Valley. Grandview and the Prosser area are commonly known as hot spots around the state for positive tests in birds and horses.

One in five infected people develop the symptoms of West Nile virus. Onset occurs from three to 14 days after the bite. Usually, the illness runs its course without medical intervention, but serious afflictions can cause neck stiffness, disorientation, coma, tremors, convulsions and paralysis, even death.

Those 50 and older are at the highest risk.

Jecha reminds people to use mosquito repellent, remove standing water and take other mosquito- prevention methods.

"A lot of times it takes this to make people aware," he said.