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Mosquito trap tests positive for West Nile Virus

The Three Rivers Mosquito Control District announced on August 27 that they had a mosquito surveillance trap that had tested positive for the West Nile Virus.

District officials are asking area residents to take extra precautions for themselves and their horses and llamas.

"While the number of adult mosquitoes is low, the risk of infection from mosquito bites has increased. We are still treating trying to further reduce the numbers, but please wear mosquito repellent and try to wear long sleeves and pants when doing activities where you might encounter mosquitoes," Dru Zeiger said.

According to the Montana DPHHS, several counties reported increased WNV activities in August, including the first three human cases. The cases have been identified in Dawson, Rosebud, and Yellowstone counties. Two horses tested positive in Hill and Pondera counties.

"With West Nile virus activity occurring in so many areas of the state right now, the best thing you can do to prevent infections is to protect yourself from mosquito bites," said DPHHS Vectorborne Disease Epidemiologist Devon Cozart. "All three human WNV cases reported this year were hospitalized, which shows just how serious this disease can be. If you are concerned you have a West Nile virus infection, please see your doctor."

West Nile Virus

(From the Montana DPHHS)

WNV infections can occur in humans or horses after a bite from an infected Culex mosquito. Increased risk of WNV transmission to humans and horses is expected to continue through October – or as long as mosquitoes are active in the state.

Preventing mosquito bites is especially important while spending time outdoors in the summer, and during peak feeding activity times for female Culex mosquitoes, which are dusk and dawn. Permethrin is an insect repellent that can be utilized to treat clothing and gear, including tents. The Environmental Protection Agency search tool offers EPA-registered insect repellents that can be applied to the skin.

Most people who become infected with WNV will not experience symptoms, but 1 in 5 do experience minor illness causing headache, rash, body aches, joint pains, fatigue, vomiting, and diarrhea. Fatigue and body aches from WNV may persist for months following infection.

Unfortunately, about 1 in 150 WNV infections result in severe WNV disease, referred to as neuroinvasive West Nile.

When neuroinvasive, WNV can cause severe neurological symptoms including disorientation, stupor, coma, paralysis, vision loss, and convulsions. WNV can be fatal or lead to long-term neurological complications. WNV can also cause severe neurological complications and death in horses.

Currently, there is no vaccine, treatment, or other targeted medication for WNV in humans, aside from supportive care for cases. A vaccine is available for horses. The vaccine is typically administered in the spring to provide optimum protection during mosquito season.

Horses cannot transmit the disease to people, but because of the severity of the disease in horses, the vaccine is a recommended core vaccine and should be given annually. Montanans are encouraged to contact their local veterinarian for questions about horses and WNV.

The mosquitoes that carry WNV rarely travel more than one mile from where they breed. So, to keep mosquitoes away from the home, it's important to empty standing water at least once per week. For items such as rain barrels, a screen can be applied to the opening to restrict mosquito access. For other mosquito bite prevention tips, check out the 4 D's of mosquito bite prevention below.

The 4 D's of Mosquito Bite Prevention:

1. DEET: Use insect repellent containing effective ingredients such as DEET or picaridin. To verify the effectiveness of insect repellent, go to the EPA's website.

2. Drain: Drain standing water around the house to prevent mosquito breeding.

3. Dawn/Dusk: Mosquitoes are most active during dawn and dusk. Stay inside or take extra precautions to prevent mosquito bites during these times.

If doors or windows are left open in the summer, make sure they're fitted with a screen to keep mosquitos out of the house.

4. Dress: When possible, wear long sleeved shirts and pants to protect against bites.

For more information about WNV protection and surveillance activities, contact the local health department or visit the DPHHS WNV website page.

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