First cases of West Nile Virus reported in Montana

State and local public health officials are reminding Montanans to avoid mosquito bites as the state’s first cases of West Nile Virus were recently reported.

Four cases of WNV have been reported, three from Dawson County and one from Garfield have been identified. In addition to the human cases, one equine case in Petroleum County and mosquitoes in Lake, Prairie, Phillips and Valley counties have tested positive for the virus.

WNV is transmitted to humans by infected mosquitoes through bites. Most, about four out of five, people infected will experience no symptoms and develop immunity. About one in five infected people develop a low grade fever, headache and muscle aches that begin a week or two after becoming infected. Generally, no treatment is needed.

However, in less than one percent of infected people, serious, life-threatening symptoms develop including headache, rash, high fever, stiff neck, mental confusion and other symptoms. Individuals who develop any of these symptoms should see their health-care provider immediately.

Mid to late summer is prime time for transmission of WNV and public health officials encourage everyone to take steps to avoid mosquito bites and prevent infection with WNV. Public health officials want to remind the public that while WNV is a concern in Montana, Zika virus is not. In fact, the mosquitoes that carry Zika virus have not been found in Montana or neighboring states.

To minimize risk of WNV, experts recommend reducing mosquito populations by removing mosquito breeding areas in and around the home. Simple steps such as draining birdbaths, wading pools or any container with still water every few days will minimize breeding sites.

Because it is not possible to eliminate all breeding sites, people are reminded to follow specific recommendations to avoid being bitten. This includes wearing and safely using insect repellent when outdoors and wearing pants and long-sleeved shirts when possible.

The 4 Ds of West Nile Virus prevention should be followed to reduce the chance of mosquito bites.

Dusk/Dawn: Peak mosquitoes biting hours are dusk to dawn. Limit outdoor activity during those times. If you must be outside, be sure to protect yourself from bites.

Dress: Wear long-sleeved shirts and pants to reduce the amount of exposed skin.

DEET: Cover exposed skin with a repellant containing the chemical DEET, which is most effective against mosquito bites.

Drain: Empty any containers holding standing water because they can be excellent breeding grounds for virus-carrying mosquitoes.

The number of WNV human cases in Montana varies from year to year. Over 200 cases were reported in 2003 and 2007, but generally the average is about 10 reported human infections each year. Cases reported are more likely to be those that are severe and about one-third of Montana cases required hospitalization.

 “No one can predict the severity of WNV season,” said Christine Mulgrew, DPHHS WNV Program Manager. “But we can protect ourselves from mosquito bites and eliminate breeding sites around your home.”

For more information go to the DPHHS website at



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