It’s that time of year again — mosquito-borne illnesses including West Nile virus and Eastern equine encephalitis (EEE) are on the rise in Massachusetts, putting a damper on end-of-the-summer picnics and BBQs. Lexington is currently categorized as having a “medium” level of risk for West Nile virus (WNV). Nearby towns including Bedford and Newton have been elevated to “high” risk of the West Nile virus (WNV), state health officials said in a statement on August 12th.
WNV-positive mosquitoes were first detected in Massachusetts on June 17th. Since then there have been 228 mosquito samples which tested positive in the state, including 84 in Middlesex County. None have been in Lexington. Additionally, there has been one confirmed animal case, a goat in Luneneberg, MA. No human contractions in the state have been reported this year.
“WNV findings in mosquitoes have accelerated rapidly over the last several weeks,” State Epidemiologist Catherine M. Brown said in a statement. “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.”
This year’s trend of West Nile virus has continued the trend of high levels from past years. In 2024, 19 human cases of WNV were reported, five of which were from people residing in Middlesex County. In 2023, there were six human cases throughout the state.
Most people who contract West Nile Virus (WNV) do not show any symptoms. When illness does occur, it is usually mild and may include fever, headache, nausea, vomiting, diarrhea, rash, or muscle aches. These symptoms often resolve on their own without medical treatment. However, adults over the age of 50 or immunocompromised are at greater risk of developing severe life-threatening complications from WNV.
Along with West Nile virus, the risk of Eastern equine encephalitis (EEE) has also been detected in southern and western Massachusetts. Lexington is currently classified as “remote” risk for EEE. Last year, eleven positive mosquito samples—including two in Concord—and two human cases were reported in Middlesex Although EEE is less prevalent than WNV, it has a higher fatality rate of about 30%, and many survivors experience long-term neurological damage.
“Both West Nile virus and EEE pose risk to the people in Massachusetts,” Public Health Commissioner Robbie Goldstein said in a statement. “The weather remains warm and somewhat humid, which increases mosquito activity. I encourage everyone to take measures to protect themselves: use mosquito repellent when outdoors, wear long sleeves and pants, and be aware of peak mosquito hours.”
State health officials also emphasized the importance of reducing mosquito habitats around homes and neighborhoods. Draining standing water from containers, cleaning gutters, and repairing screens can significantly cut down mosquito populations. Residents are further urged to check the state’s daily Arbovirus Surveillance Information updates, which track positive findings of WNV and EEE across Massachusetts.
Horse owners and other animal caretakers are reminded to consult their veterinarians about mosquito repellents and vaccinations, and to report any suspected cases of mosquito-borne illness in animals to the appropriate state agencies. If an animal is suspected of having WNV or EEE, owners are required to report to the Department of Agricultural Resources, Division of Animal Health, and the Department of Public Health.
If you or someone you know is experiencing symptoms of WNV or EEE, contact a health care provider immediately.