Mosquito season is tightening its grip on western Massachusetts as state health officials have raised the West Nile virus risk to moderate in 10 more Berkshire County communities, leaving only six towns in the county below that level.
The change follows Massachusetts' sixth confirmed human case of the virus and adds urgency for residents spending time outdoors as seasonal transmission typically peaks in late August and early September, according to The Berkshire Eagle.
Here's what to know
The Massachusetts Department of Public Health has moved Sandisfield, Otis, Monterey, Tyringham and Lee, along with Stockbridge, West Stockbridge, Richmond, Alford, and Egremont into the moderate-risk category.
In practical terms, that means human infection is considered likely to occur or may already have occurred in those areas.
The state's sixth human case was identified in a Suffolk County man in his 70s.
His symptoms began Aug. 26, and the Department of Public Health disclosed that he developed encephalitis, an inflammation of the brain.
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The Centers for Disease Control and Prevention describes West Nile virus as the most common mosquito-borne illness in the United States.
No vaccine or treatment for it exists, and while many infections are mild or go unnoticed, about 1 in 150 cases can become severe and potentially life-threatening.
People older than 50 face a higher risk of serious illness.
More background
Despite the elevated warning level, Berkshire County still has not recorded a human case of West Nile virus.
The county has, however, reported three more positive mosquito samples: one collected in Lanesborough on Aug. 25 and two taken in Otis and Richmond on Aug. 27.
Only parts of Middlesex and Suffolk counties are classified as high risk for West Nile virus.
Berkshire County, meanwhile, and most of the state remain at low risk for Eastern Equine Encephalitis, another mosquito-borne illness.
State officials have detected EEE in 13 mosquito samples statewide, but no human infections have been reported.
What can be done?
The Department of Public Health recommends eliminating standing water twice a week, as even small amounts in buckets, flowerpots, gutters, and toys can become breeding sites.
Officials also advise fixing window and door screens, wearing long sleeves from dusk to dawn, and applying mosquito repellent outdoors.
Families with infants are being told to cover baby carriages and playpens with mosquito netting.
In a prepared statement, Public Health Commissioner Robbie Goldstein addressed people in the affected areas ahead of Labor Day weekend.
"As we go into the holiday weekend, it is easy to think of backyards, barbecues, and fun. I also want people to think about mosquitoes. This is the time of year when people get exposed to the West Nile virus and Eastern Equine Encephalitis," Goldstein cautioned.
Where can I learn more?
Massachusetts' updated risk map is one piece of a wider stretch of West Nile activity showing up in both mosquito testing and human cases far beyond Berkshire County. It's a reminder of how quickly late-summer detections can turn into broader public health warnings.
• Massachusetts detected its first West Nile-positive mosquitoes as seasonal surveillance ramped up.
• By June, the CDC warned that West Nile cases hit 48, with Arizona leading the nation.
• In Ohio, health officials reported that the rate of illness was climbing among residents.
• In Colorado, officials tied the first case of 2026 to backyard mosquito risks.
• The CDC says greater public awareness is still needed as mosquito threats spread.
Those reports help explain why Berkshire County residents are being told not to shrug off the latest risk change. The local uptick happens regularly, and early precautions still matter.
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