BOSTON — The Massachusetts Department of Public Health raised the risk level for West Nile Virus, or WNV, to high in many communities, urging residents to protect against the mosquito-borne disease.

“WNV findings in mosquitoes have accelerated rapidly over the last several weeks,” State Epidemiologist Catherine Brown said. “We are now in the peak time for transmission of mosquito-borne disease to people, and it is important for people to know that so they can take steps to protect themselves.”

Health officials raised the risk level for several municipalities, including Boston, due to “ongoing evidence of mosquito samples carrying the virus.” Since June 17, DPH said,168 WNV-positive mosquito samples have been detected across 12 Massachusetts counties.

One case of West Nile has also been confirmed in a goat in Lunenburg this year, DPH said. No human cases have been reported so far this summer.

The virus is the leading cause of mosquito-borne disease in the continental U.S., according to the CDC. There are no vaccines or medicines in use for the disease, the CDC states. Though many infected people do not feel sick, some develop symptoms like a fever and few become seriously or fatally ill.

In addition to Boston, the WNV risk level was raised in Acton, Bedford, Billerica, Brookline, Carlisle, Chelmsford, Dracut, Lowell, and Newton.

DPH also raised risk levels to moderate for another mosquito-borne disease, Eastern equine encephalitis, in several communities. There have been seven EEE-positive mosquito samples detected in the state this year.

“Both West Nile virus and EEE pose risk to the people in Massachusetts,” Public Health Commissioner Robbie Goldstein said. “The weather remains warm and somewhat humid, which increases mosquito activity.”

In 2024, there were 19 human cases of West Nile reported in Massachusetts, and four human cases of EEE, one of which was fatal.

The Boston Public Health Commission warned that people who are over the age of 50 or immunocompromised have a higher risk of developing serious illness from West Nile. Symptoms may include high fever, severe headache, confusion, lack of coordination, and muscle weakness, and residents suffering should “contact a health care provider immediately.”

Health officials urge residents to consider precautions like wearing insect repellant outdoors, being wary of peak mosquito hours from dusk to dawn, covering skin while outdoors, draining standing water where mosquitos may breed, and installing screens in windows and doors.

More information about mosquito-borne diseases and safety measures can be found at mass.gov/mosquito-borne-diseases.

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