A mosquito sample collected in Yellowstone County tested positive Wednesday for West Nile virus, adding the county to a list of two others that tested positive for the virus.

Cascade, Sheridan, and Yellowstone counties have all had a positive mosquito sample for the virus, however, no human cases have been identified in Montana so far this year, according to the Montana Department of Public Health and Human Services.

“Late July and early August is when we typically see (West Nile virus) activity pick up here in Montana,” said Erika Baldry, a DPHHS communicable disease epidemiologist, in a press release. “Our season can begin as early as July and because it can take some time to become ill, we can receive reports of ill individuals as late as October.”

In 2018, 51 West Nile virus human cases and one related death were reported, along with 50 horse cases. Seven counties had positive mosquito pools. 

Most people who become infected with West Nile experience no symptoms, but 1 in 5 will develop mild symptoms like headaches and rashes. Fewer than 1 out of 150 may become severely ill with encephalitis, meningitis, or inflammation of the brain or surrounding tissues.

People who develop these symptoms should see their healthcare provider, the release said.

In Montana, the mosquito species Culex tarsalis is effective in transmitting the virus to people and horses.

DPHHS recommends using insect repellent with DEET or picaridin, draining standing water around a home to prevent mosquito breeding, staying inside during dusk and dawn when mosquitoes are active, and wearing long sleeved shirts and pants to protect from bites.

More information can be found on the DPHHS website.

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