West Nile virus, a potentially fatal illness for humans, has been found in a dead bird in King County.

Tests last week of a dead crow that was found in Kirkland on Sept. 15 confirmed the presence of the virus in the bird, the Seattle-King County Public Health Department reported Tuesday. The findings mean county residents could become infected by the virus this year.

West Nile is spread to people by mosquitoes that have bitten infected birds.

“While the days are growing cooler and there may be fewer mosquitoes around, this West Nile-positive bird is a reminder that it’s still important to protect yourself against mosquito bites,” said Dr. David Fleming, director of the Health Department. “The risk of contracting the virus isn’t over for this season.”

West Nile can cause serious illness, especially in older adults. In 2008, more than 700 people in the United States have experienced symptoms of the virus, and 11 have died. In Washington alone, multiple birds, mosquitoes and horses have tested positive for West Nile this year. A King County resident is among two people statewide who are “probable” for West Nile virus, pending test results, officials said. In addition, another King County resident who donated blood was discovered to be infected by West Nile infection. Officials said it’s believed that all three individuals contracted the virus outside of King County, however.

Most people with West Nile virus don’t have any symptoms or feel sick. But about 20 percent of people who are infected will experience fever, headache, body aches and occasionally swollen lymph glands or a rash and be ill for several weeks. In fewer than 1 in 150 cases, West Nile may cause inflammation of the brain, which requires hospitalization.

There is no vaccine for the virus in humans.

The crow from Kirkland is the first bird to test positive for West Nile virus in King County in two years. It was discovered through the Health Department’s tracking of dead birds and the locations where they’re found, as well as trapping and testing mosquitoes. The crow was sent to the Washington Animal Disease Diagnostic Laboratory in Pullman for tests that confirmed the virus.

More than 1,300 dead birds have been reported this year to the Health Department, and 187 mosquito pools have been tested.

Birds – especially crows and jays – are an important indicator of West Nile because they die quickly from the disease, officials said.

Before the latest one, no birds in King County had tested positive for West Nile since October 2006, when the virus was found in six birds and one horse, officials said.

Horses are at high risk for West Nile, but a vaccine is available through veterinarians, according to the Health Department. Other animals, such as cats and dogs, are unlikely to become ill from the virus, officials said.

Testing of dead birds will end in late October, but dead ones can be reported year-round to the Health Department at (206) 205-4394 and www.metrokc.gov/health/westnile/deadbird.htm.

The department reports findings at www.metrokc.gov/health/westnile.