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Officials urge mosquito caution as recorded West Nile Virus cases rise

State and local health officials are urging Montanans to protect themselves from mosquito bites as the state health department identifies more cases of West Nile Virus in several counties.

Seven residents in McCone, Richland, Dawson, Rosebud and Yellowstone counties have tested positive for the virus this year, according to surveillance data from the Department of Public Health and Human Services last updated Friday. The virus has also been detected in mosquito pools and in horses, bringing the total number of counties with recorded West Nile Virus activity so far in 2023 to seventeen.

Three of the infected residents live in Yellowstone County, according to a Tuesday release from Riverstone Health communications coordinator Pat Zeller. Of those, two were hospitalized for severe brain and neurological symptoms. One person has since been discharged, Zeller said, while the other remains hospitalized in Billings.

Many people infected by the virus do not experience symptoms, state and local health officials say. But some, roughly 1 in 5, might experience a fever lasting between three and six days and other mild symptoms.

Although very rare, severe cases of West Nile Virus may lead to symptoms of encephalitis or meningitis, the swelling of the brain or protective membranes around the brain and spinal cord. Some of the resulting symptoms, including disorientation, coma, tremors, convulsions, vision loss, numbness and paralysis, can last several weeks and may be permanent, according to the state health department.

West Nile Virus is most commonly spread through bites from an infected mosquito. There is no vaccine to protect against the virus available for humans.

Health officials announced the year's first Montana detection of the virus in Blaine County in July. While no human cases of West Nile Virus were reported in 2022, the Montana state health department has tallied as many as 51 cases during a single summer in 2018. The first cases of West Nile Virus in Montana were identified in 2002.

"Mosquito surveillance this year has identified a large proportion of active Culex species mosquitoes, the type of mosquitoes that can carry and transmit WNV," Devon Cozart, a vectorborne disease epidemiologist with the state health department, said in the July announcement. "The best way to prevent mosquito-borne diseases, including WNV, is to protect yourself from mosquito bites."

In addition to using bug repellent that specifically wards against mosquitos with the ingredients of DEET or picaridin, health officials recommend avoiding the outdoors at dawn and dusk and wearing tightly woven, loose-fitting clothing to protect against mosquito bites. Draining standing water, which can give mosquitos more places to lay their eggs, is also commonly recommended as a preventative measure.

Protective clothing should cover arms, legs and feet. Infants and young children can be protected by mosquito netting that covers strollers and baby carriers.

No deaths from West Nile Virus have been recorded in the state so far this year. Two virus-related deaths were recorded in Montana in 2016 with another in 2018. Last year, the Centers for Disease Control and Prevention tallied 90 deaths attributed to West Nile Virus nationwide.

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