Yellowstone County is leading the state in cases of West Nile virus so far this year, according to public health data.

As of Sept. 12 Yellowstone County has had eight cases the mosquito-borne virus, per the Montana Department of Public Health and Human Services. Since pools of mosquitos in Montana tested positive back in July, confirmed cases in humans and horses have spread across most of the eastern portion of the state. The latest information from DPHHS came as nationwide West Nile infections in 2025 are 40% higher than normal.

Of the eight cases confirmed in Yellowstone County four were instances of people hospitalized with severe symptoms, said Riverstone Health Communicable Disease Program Manager Stacie Pannell.

“It’s more of these cases that we see,” she said, “because those are

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