First mosquitoes with West Nile virus in Oregon this year found in Malheur County

West Nile virus, which is spread by mosquitoes, has been detected in mosquitoes at a testing site in Malheur County, Ore., according to Oregon Public Health officials.

The mosquitoes, found in Vale, are the first to test positive for the disease in Oregon in 2021.

Health officials are advising people in Malheur County to take precautions against mosquitoes to avoid the risk of infection, including preventing mosquito bites. West Nile virus is spread to humans through the bite of an infected mosquito. Most infected people will show little or no signs of disease. 

About one in five people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with febrile illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months. It is important that you contact your health care provider if you experience any of these symptoms.

The incubation period is usually two to 14 days. Rarely, infected individuals may develop neuro-invasive disease (infection of the brain or spinal cord) that can be severe or may cause death. This is especially of concern to people 50 and older, people with immune-compromising conditions, and people with diabetes or high blood pressure. 

Communities and individuals living in or spending significant time outdoors, particularly near irrigated land, waterways, standing water, and used tires—including those working in agriculture, such as migrant and seasonal farm workers—may be at increased risk of mosquito bites and related diseases.

The number of mosquito pools—samples of about 50 mosquitoes—that test positive in any area may indicate the risk of human exposure and infection, said Emilio DeBess, D.V.M., public health veterinarian at the Oregon Health Authority’s Public Health Division. He recommends people and animals be protected against mosquito bites.

“Although mosquitoes are an inevitable part of summer, mosquito bites don’t have to be—they are preventable,” DeBess says. “You can take simple steps to protect yourself and reduce the risk of contracting West Nile disease.”

DeBess offers these tips for protecting yourself against mosquitoes:• Eliminate sources of standing water that are a breeding ground for mosquitoes, including watering troughs, bird baths, ornamental ponds, buckets, wading and swimming pools not in use, and old tires.• When engaged in outdoor activities at dusk and dawn when mosquitoes are most active, protect yourself by using mosquito repellants containing DEET, oil of lemon eucalyptus or Picardin, and follow the directions on the container.• Wear long-sleeved shirts and long pants in mosquito-infested areas.• Make sure screen doors and windows are in good repair and fit tightly.

While risk of West Nile disease is low, a handful of people get it each year in Oregon. The virus also affects wildlife and domesticated and farm animals.

In 2019, nine human cases of West Nile virus infection were reported in Oregon, with 85 mosquito pools and seven horses also found to be positive for the virus. In 2018, there were two human cases, with 57 mosquito pools and two horses testing positive. Last year was relatively mild for West Nile, with only three mosquito pools and one bird found to be positive for the virus.

People should consult their health care providers if they have these symptoms. Health care providers can contact the Malheur County for information on West Nile virus testing.

Additional information about West Nile virus: 

Oregon Health Authority website: http://public.health.oregon.gov/DiseasesConditions/DiseasesAZ/WestNileVirus/Pages/survey.aspx

U.S. Centers for Disease Control and Prevention: http://www.cdc.gov/ncidod/dvbid/westnile

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