State public health officials said Thursday that West Nile virus was detected in mosquitoes in Berkshire County, marking the first positive sample of the year.

The virus is transmitted to people through bites from infected mosquitoes, and Massachusetts last year logged nine human cases, the Department of Public Health said. The positive sample came from Clarksburg.

“WNV can cause serious illness, especially in those who are more vulnerable,” Public Health Commissioner Dr. Robbie Goldstein said. “Taking simple measures such as using a mosquito repellent with an EPA-registered ingredient, wearing clothing to reduce exposed skin, draining standing water, and repairing window screens can help reduce the risk of mosquito-borne illness throughout the summer.”

People over age 50 are at higher risk for severe disease and can experience symptoms such as a fever and flu-like illness, DPH said. Most infected people will not have symptoms.

No human or animal West Nile virus cases have been detected so far this year, health officials said. There’s also no evidence yet of Eastern Equine Encephalitis, another virus spread through infected mosquito bites.

In 2025, DPH announced its first positive sample on June 17.

“With warmer weather and summer officially beginning this week, it is the time of year when we typically begin detecting West Nile virus in mosquito populations,” Goldstein said.