West Nile virus found in Acton mosquito sample
The Massachusetts Department of Public Health listed Acton’s risk level as “moderate” as of Thursday.
State and local health officials are sounding the alarm about West Nile virus after experts detected the infection in a Acton mosquito sample.
West Nile is transmitted to humans through mosquito bites. The state tracks the virus annually and monitors when it shows up in local mosquito populations.
Officials collected nine Acton mosquito samples on July 23. The Massachusetts Department of Public Health announced the positive test in one group of insects on Thursday.
Most people with West Nile show no symptoms, according to the DPH. In rare cases, people can develop serious conditions, including encephalitis or meningitis.
The state listed Acton’s risk level as “moderate” as of Thursday. Experts urge people to use insect repellent, wear long sleeves and pants, and consider rescheduling outdoor activities in the evening or early morning.
People should also drain standing water to limit spots for mosquitoes to lay their eggs, and residents should install or repair window and door screens.
Beyond Acton, West Nile has been detected in 58 other samples throughout Massachusetts this year. There have been no reported human cases.
Eastern equine encephalitis, a rare but dangerous mosquito-borne disease, has appeared in two Massachusetts samples in 2025 — though neither was in Acton. There have been no human cases.
Positive EEE samples last year led to pesticide spraying in town and prompted Acton’s public schools to restrict outdoor athletics.
Acton’s EEE risk was still classified as “low” on Thursday afternoon.
While West Nile can be dangerous, the risk of death or severe brain damage from EEE infections is higher.
Acton Public Health Director Melanie Dineen said she wants people to know about West Nile and be diligent, “but it’s not the same level of where we’re going to implement spraying.”
“I just want people to be aware and just be careful,” she told The Acton Bridge.
Positive West Nile samples often happen in summer, but Dineen said it’s “not as common” for samples gathered outside Route 128. Often West Nile clusters closer to Boston, she said, while EEE appears in central and western Massachusetts. The Acton Health Department has more information about mosquito safety online at concordma.gov/3587/Mosquito-Information.
