A pierce County man has been diagnosed with the first case of West Nile virus acquired in Washington state, and his wife also probably has...

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A Pierce County man has been diagnosed with the first case of West Nile virus acquired in Washington state, and his wife also probably has had the disease, state health officials said Wednesday.

The Gig Harbor residents, both in their 40s, had only relatively mild symptoms of fever and rash, which started in late July, and have recovered. They had not recently traveled out of state before becoming ill.

A confirmatory blood test for the man’s wife is pending at the Centers for Disease Control and Prevention (CDC).

West Nile virus infection can be deadly, but among people who get the mosquito-borne virus, only about 1 in 150 have severe effects such as brain swelling. About four of five never have any symptoms.

The first Washington state case of the disease, confirmed Wednesday, comes as Idaho has logged the most in the nation this year with at least 325 reported cases, including five deaths, according to the CDC. Idaho health authorities this summer even resorted to aerial spraying of insecticides. No such measures are planned in Washington, though active surveillance of the disease continues.

Disease experts have puzzled over why Washington has escaped with only one human case acquired in the state, especially with so many cases in Idaho. More than 21,000 cases, including more than 830 deaths, have been reported nationwide since the virus was first detected in the U.S. in 1999.

“I have no idea why. … It makes no sense to me,” said Dr. Jo Hofmann, state epidemiologist for communicable diseases.

How to avoid West Nile virus

The virus is carried by mosquitoes, which bite infected birds and spread it to humans. It does not spread by direct contact between humans or contact with horses. Avoid mosquitoes by staying indoors at dawn and dusk, when mosquitoes are most active, or wear repellent, if you must go out. Eliminate standing water to prevent mosquitoes from breeding.

West Nile virus symptoms

Only about 20 percent of those infected have symptoms, and only about 1 in 150 have severe symptoms that can lead to death. Symptoms begin three to 14 days after being bitten by an infected mosquito. People older than 50 are at higher risk of becoming severely ill.

Mild symptoms: fever, headache, body aches, nausea, vomiting, rash, swollen lymph glands. Can last from a few days to several weeks.

Severe symptoms: high fever, headache, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Can last several weeks and nervous-system damage can be permanent.

Sources: Centers for Disease Control and Prevention, Washington state Department of Health

For more information

Washington state Department of Health: www.doh.wa.gov/phepr/handbook/westnile.htm

Centers for Disease Control and Prevention: www.cdc.gov/ncidod/dvbid/westnile/wnv_factsheet.htm

Hofmann said there have probably been mild cases in Eastern Washington this summer, but those infected were never sick enough to see a doctor. The disease does not pass by direct contact between humans.

The Pierce County man, who lives in a rural area, felt ill in late July, but went traveling with his wife anyway. He had been bitten by mosquitoes in mid-July and probably was infected then, said Donn Moyer, a spokesman for the state Department of Health.

The man still felt bad when he returned in late August and blood tests confirmed that he had the disease, Moyer said. He was not identified for privacy reasons.

Hofmann said five to 10 human cases of the disease have been reported each year in Washington, but investigations showed the infections all occurred in other states.

Surveillance by health authorities, however, has shown that the virus has been in the state at least since 2002. Several horses and dead birds have been found to be infected, including a quarter horse in Yakima County this summer. The virus also was found in mosquitoes in two Eastern Washington ponds last summer.

Hofmann said the threat of the virus is decreasing as the days grow colder and mosquitoes are less active or become dormant.

West Nile virus is carried mainly by birds. Mosquitoes bite infected birds, then pass it to humans and to horses, which are more vulnerable than humans.

Crows, magpies and jays usually die from the virus, and state and local health officials have been tracking dead-bird reports and monitoring mosquito pools statewide.

Humans can avoid the disease by avoiding mosquitoes, health authorities say. That means wearing repellent and long sleeves and pants outside, and emptying standing water that can enable mosquitoes to breed.

Hofmann pointed out that some areas of the state are still warm.

“It’s possible we may see additional [West Nile] cases,” she said.

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

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