09:08 AM PDT on Friday, September 23, 2005

Associated Press

CENTRAL POINT, Ore. -- A Central Point woman has contracted the West Nile virus, the sixth human case in Oregon this year.

(kgw.com Graphic)

The unidentified woman reported experiencing symptoms, including a fever, headache and fatigue on Aug. 21, officials said. The Jackson County Health and Human Services Department took a sample of her blood and sent it for testing -- which takes several weeks -- to the U.S. Centers for Disease Control and Prevention in Atlanta.

Statewide, there have been five other human cases of the virus, two contracted in Malheur County and one in Lane County, said officials with the Oregon Department of Human Services.

Another two cases in Benton and Marion counties are believed to have been contracted in California, officials said.

But fewer cases of the virus were reported in humans than expected in Oregon, as the arrival of fall signaled the end of the mosquito season, officials said.

West Nile arrived in Oregon in 2004, sickening five people, and killing 19 birds and 22 horses.

Typically, the virus shows little activity the year it arrives in a region, as it did in Oregon in 2004. The following year, infections generally soar.

But for reasons that aren't clear, the virus does not seem to be following that pattern in Oregon and Washington state.

Dr. Emilio DeBess, state public health veterinarian and medical epidemiologist, said mosquito-control programs in Jackson and Klamath counties in southern Oregon are helping to keep the virus from moving north into more heavily populated areas.

The virus is transmitted by infected mosquitoes that feed on birds, giving the disease two different ways to spread -- by insect and by bird.

"We don't have any control over the birds," DeBess noted.

But he said county mosquito programs can dramatically reduce the speed with which the virus travels. DeBess said Jackson and Klamath counties seem to be serving as "gatekeepers," slowing the spread of the virus from California.

California had the most West Nile cases this year with 608 human infections and 13 deaths.

Eugene Papineau, manager of the Jackson County Vector Control District, said his crews spread larvicide and spray mosquito fog over 50,000 to 80,000 acres a season and answer 3,000 to 4,000 requests for spraying.

"I would like to think our program is making an impact locally," Papineau said.

Meanwhile, the virus seems to be making its way into Eastern Oregon by way of Idaho. It has established itself in Malheur County, where four of last year's five cases originated.

The northernmost Oregon county to report the virus is Umatilla, where a horse was reported infected last Thursday, DeBess said.

But he said he does not expect many more human cases this year.

"I usually say the season ends in the middle to the end of September," DeBess said. "We're pretty much at the end of it."