UMATILLA — West Nile virus, a flu-like disease spread by mosquitoes, has been detected in mosquitoes at a testing site in Umatilla County.

Oregon Public Health officials say the the mosquitoes, found in Umatilla, are the first to test positive for the disease in Oregon in 2019. The mosquitoes were collected last week by the West Umatilla Mosquito Control District. The Oregon State University Veterinary Diagnostic Laboratory in Corvallis confirmed the discovery.

West Nile virus spreads to humans via the bite of an infected mosquito. About one in five infected people may show signs of the virus. People at risk of serious illness include individuals 50 and older, and people with immune-compromising conditions, such as diabetes and high blood pressure.

West Nile symptoms include fever above 100 degrees and severe headache, stiff neck, mental confusion, muscle weakness, shaking, paralysis and rash. People should contact their health care provider if experiencing any of these symptoms.

The incubation period is usually two to 14 days. Rarely, infected individuals may develop severe brain or spinal column infections that could cause death.

The number of mosquito pools — samples of about 50 mosquitoes — testing positive in any area could lead to infection. Dr. Emilio DeBess, veterinarian at the Oregon Health Authority’s Public Health Division, recommends people and animals guard against mosquito bites.

“It’s very easy for people to prevent bites from mosquitoes that may carry West Nile virus,” DeBess says. “Although the risk of contracting West Nile virus is low, people can take simple precautions to keep these insects at bay if they’re headed outdoors.”

DeBess recommends eliminating sources of standing water that are a breeding ground for mosquitoes, including watering troughs, bird baths, clogged gutters and old tires.

Use mosquito repellent when engaged in outdoor activities at dusk and dawn when mosquitoes are most active. Wear long-sleeved shirts and long pants in mosquito-infested areas.

Make sure screen doors and windows are in good repair and fit tightly.

During the 2018 mosquito season, there were two human cases of West Nile virus in Harney and Clackamas counties. The virus was found in one bird, 58 mosquito pools and two horses. In 2017, seven humans, 92 mosquito pools, five horses and one bird tested positive for West Nile. The virus also can be found in chickens, squirrels and dogs.

Health officials say climate change effects, such as increased temperature and changes in rainfall, mean longer mosquito seasons and are contributing to the spread of West Nile virus.

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Contact Kathy Aney at kaney@eastoregonian.com or 541-966-0810.