The Washington state Department of Health confirmed yesterday that a Spokane-area woman has preliminarily tested positive for the West Nile virus, the first case in a human in Washington state.

The case has been labeled as "probable" until further tests are done by the state Public Health Laboratories and the federal Centers for Disease Control and Prevention (CDC). It would make Washington the last state in the lower 48 where the virus spread to humans.

CDC results probably will come back in a couple of weeks, Donn Moyer, state health department spokesman, said last night.

He said the local health department in Spokane learned about the woman's "presumptive positive test" from a local laboratory and health-care provider; the local health department then notified the state, he said. It was unclear when each agency learned of the test.

Moyer said a Yakima man initially thought to have contracted the virus in August 2003 also preliminarily tested positive for the virus. Health officials later learned he instead suffered from a common intestinal virus.

"The preliminary tests have gotten a lot better since then," Moyer said.

The Spokane-area woman, who is in her 20s, had not traveled outside the state before getting sick. She had been briefly hospitalized, he said.

"The disease is not spread person-to-person, so the case does not represent a threat to public health," said state health officer Dr. Maxine Hayes. "We've been expecting West Nile virus to begin affecting people in our state as we've watched it move across the country. "

For the past six years, more than 17,000 people in the U.S. have suffered the withering fevers, aches and exhaustion of West Nile virus.

More than 650 of them died after developing severe neurological complications, including tremors, stupors and comas.

The mosquito-borne virus has marched westward across the country, spreading slowly into the Northwest. Three human cases each were diagnosed in 2004 in Oregon and Idaho. Another 771 were identified in California.

How it spreads

West Nile is spread long distance by birds, which are bitten by mosquitoes that then bite other birds, humans and animals. The sometimes-lethal virus can sicken humans, horses and certain birds, including corvids (such as crows, ravens, magpies and jays) and raptors (such as hawks, owls and eagles).

In 2002, the virus made its only appearance in Washington — in four dead birds found in Snohomish, Pend Oreille, Thurston and Pierce counties; and in two horses in Island and Whatcom counties. But the virus didn't get established, probably because not enough birds were infected.

"There must be enough birds infected for the mosquitoes to feed off," says Tom Gibbs, a West Nile expert with the state Department of Health.

Only one in five humans ever has any symptoms when infected with the virus. About 1 in 150 has severe neurological infections, which can lead to brain inflammation, paralysis and, rarely, death.

Surveillance, but no cure

Scientists have not yet developed either a vaccine or a cure for West Nile, though several experimental treatments and a vaccine are being explored. For now, doctors are able to treat only symptoms of the disease.

State and local health authorities are conducting a range of surveillance activities to provide early warning of the arrival of the virus. Blood banks also test donors' blood for the virus.

Public Health-Seattle & King County has 12 mosquito traps placed around the county. As the trapping program gets under way, the mosquitoes are being identified by species. But soon lab workers will begin testing catches for West Nile virus.

Health workers from 24 Washington counties are doing such trapping. Nineteen of the 60 mosquito species that can carry the virus have been found in the state. But only two species usually infect humans, said Gibbs, of the Department of Health.

Public Health and other government agencies also monitor bodies of water on their property for mosquito larvae to gauge how fast mosquitoes are breeding. The heart of the monitoring program, however, is with dead-bird reporting. Every county in the state has some type of program for residents to report the birds, Gibbs said. Typically, as in King County, the location of the bird is recorded, and if a pattern begins developing in one area, some are sent to a lab for testing. More than 1,000 birds already have been reported to health officials in King and Snohomish counties this year, but none has tested positive for the virus.

Health authorities are encouraging government and private-property owners to eliminate water that stands for more than seven days, so mosquitoes will not have time to hatch.

The city of Seattle, for example, will consider emptying catch basins that become breeding grounds or stocking them with larvae-eating fish.

Eva Constantaras: 206-464-2537 or econstantaras@seattletimes.com

Warren King: 206-464-2247 or wking@seattletimes.com