A Mendocino Coast woman is the first person to be diagnosed with West Nile virus on the North Coast this year.

She also is the first person known to have contracted the mosquito-borne disease within Mendocino County, said Jennifer Dutton, communicable disease program manager for the Mendocino County Health and Human Services Agency.

"This is our first resident who has had no known travel outside the county," she said.

The two other Mendocino County residents who have been diagnosed with West Nile virus, both in 2007, are believed to have been bitten by mosquitoes infected with the virus while they were elsewhere, she said.

The woman, diagnosed in August, did not suffer serious problems as a result of the disease, Dutton said. An estimated 80 percent of people who are infected are unaware of it because their symptoms are mild or nonexistent, she said.

The woman was diagnosed after her doctor ran a test, Dutton said. She would not give additional information about the woman or what made her doctor test for the virus, citing privacy concerns.

Neither Sonoma County nor Lake County has reported a human case of West Nile virus this year.

Lake County has reported a horse and a bird with the virus, and Sonoma County has reported four birds.

Mosquito traps in both counties have found insects that were infected with West Nile virus.

Mendocino County, which also has had several dead birds test positive for the virus, does not trap mosquitoes.

North Coast health officials say so far this has been a mild year for the disease. "This is our lightest year since West Nile was detected in the county in 2004," said Lake County Vector Control District Director Jamesina Scott.

The state Department of Public Health has reported 236 human cases of West Nile virus infections so far this year, but it does not include the Mendocino County case.

Most of the reported infections were found in Southern California. There were 77 cases reported in Los Angeles, 45 in Orange County, 40 in Riverside County and 10 in San Bernardino County, according to the state Department of Public Health.

Five people have died from the virus this year, all in Southern California, said Suanne Buggy, a spokeswoman for the department.

West Nile virus is spread through the bites of mosquitoes, which become carriers when they feed on the blood of infected birds.

Older people and those whose health already is compromised are at greatest risk, Dutton said.

Symptoms in more extreme cases include fever, headache, nausea, body aches, stiff neck, restlessness, stupor, delirium and convulsions.

The best way to avoid the disease is to avoid mosquitoes and prevent them from breeding, Scott said.

Officials recommend staying indoors at dawn and dusk, using insect repellent when outdoors during mosquito season and eliminating standing water, where the insects breed.

You can reach Staff Writer Glenda Anderson at 462-6473 or glenda.anderson@pressdemocrat