West Nile Virus found in Lewis and Clark County mosquitoes

Posted at 8:55 PM, Jul 25, 2018
and last updated 2018-07-26 00:19:15-04

HELENA – West Nile Virus (WNV) has been detected in mosquitoes in Lewis and Clark County, prompting local health officials to advise steps to prevent mosquito bites.

So far, health officials have confirmed no cases of illness in people or horses in Montana, but the virus has also been found in mosquitoes in Cascade County. Last year, there was a single human case of WNV in Lewis and Clark County.

“We have an unusually high number of mosquitoes this year due to all the flooding and moisture,” said Laurel Riek, environmental health specialist with Lewis and Clark Public Health. “Mosquito counts in the traps are around 4,000 this year, compared to about 100 last year.”

She also noted that the virus is showing up earlier than usual.

“These factors increase the risk of human exposure to the disease, which can be very serious,” Riek said. “So we urge people to take precautions to protect themselves. The virus is transmitted by mosquitoes. If you prevent the bite, you prevent the illness.”

The health department recommends the “four Ds” to reduce the chances of getting infected with WNV:

Dawn and dusk. When possible, avoid spending time outside at dawn and dusk when mosquitoes are most active.
Dress. Wear shoes, socks, long pants, and a long-sleeved shirt when outdoors for long periods of time or when mosquitoes are most active. Clothing should be light-colored and made of tightly woven materials to keep mosquitoes away from the skin.
Drain. Reduce the amount of standing water in or near your property by draining or removing it. Mosquitoes often lay eggs in areas with standing water.
DEET. Use an insect repellent that contains DEET or picaridin. Other insect repellents seem to be less effective. Be sure to follow the product guidelines when using insect repellant.

Most people who get West Nile Virus don’t develop any symptoms, but about 1 in 5 may experience fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Most recover, but the fatigue and weakness can last for weeks or months.

About 1 in 150 people who are infected with WNV develops a severe illness affecting the central nervous system, such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).

Symptoms of severe illness include high fever, headache, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis.

Severe illness can occur in people of any age, but people over 60 years old are at greater risk. People who have received organ transplants and people with certain medical conditions, like cancer, diabetes, hypertension, and kidney disease, are also at greater risk.

See your health-care provider if you develop symptoms.

More information about WNV is available at