BAKER CITY — For the first time since 2017, the West Nile virus has been detected in mosquitoes trapped in Baker County.

The virus, which mosquitoes can transmit to people, was found in mosquitoes trapped earlier this summer in Keating Valley, about 15 miles east of Baker City, according to the Baker Valley Vector Control District.

Last year, for the first time in several years, there were no positive tests for West Nile virus in mosquitoes caught in Baker County. Matt Hutchinson, who manages the 200,000-acre Vector Control District, which includes most of Baker, Bowen and Keating valleys, sent more than 250 “pools” of mosquitoes to a lab in Corvallis for virus testing.

(Each pool consists of 10 to 50 adult mosquitoes.)

During the previous several years the first confirmation of West Nile virus in Baker County mosquitoes typically happened in July or early August.

The absence of a positive test during the 2018 mosquito season was “really surprising,” Hutchinson said.

So far this summer, West Nile virus has been detected in mosquitoes in Baker and Umatilla counties, according to the Oregon Health Authority. There have been no human cases of the virus this year in Oregon. Last year there were two, one in Harney County and one in Clackamas County.

Most people who are bitten by an infected mosquito never develop any symptoms, according to state health officials.

About 20 percent of people who are infected by a mosquito bite come down with a fever or other symptoms.

About 1 in 150 people become seriously ill. People at higher risk of serious complications are those 50 and older, and those with pre-existing conditions that affect their immune systems, such as diabetes and high blood pressure.

Officials advise Baker County residents to reduce the risk of being bitten by mosquitoes on their property by draining sources of standing water that can breed mosquitoes, such as watering troughs, bird baths, clogged gutters and old tires.

When outside, especially around dawn and dusk when mosquitoes are more active, use a repellent containing DEET, oil of lemon eucalyptus or Picardin, and wear long-sleeved shirts and long pants.

Hutchinson said the species of mosquitoes that hikers and campers in the mountains typically deal with are “snowmelt” mosquitoes that aren’t usually carriers of West Nile virus.

Between 2004 and 2018, there were 185 human cases of West Nile virus in Oregon, and three of those people died.

A majority of the human cases — 100 — happened in just two years, 2006 and 2007. There was one death in each of those years, one of those in Baker County.