Mass. DPH raises risk level for West Nile virus

By Canton Citizen

The risk of contracting West Nile virus (WNV) is on the rise across Greater Boston and beyond following the announcement of the state’s first human cases of the virus this year along with a recent uptick in the number of WNV-positive mosquito samples reported by the state Department of Public Health.

Since the start of the seasonal testing program in June, a total of 184 mosquitoes have tested positive for West Nile, including one sample collected in the town of Canton on Monday, August 17. Positive samples have also been recorded in the towns of Dedham and Avon over the past few weeks. As a result, the risk level for WNV has been elevated from “low” to “moderate” in dozens of Massachusetts cities and towns, including Canton, and it was recently raised to “high” in the city of Boston and five other adjoining communities.

“West Nile virus can be a devasting disease, especially for those who are older or have compromised immune systems,” said Mass. Public Health Commissioner Dr. Robbie Goldstein. “The end of August is frequently a time for people to enjoy being outside before the start of the school year and the arrival of fall, but I want to remind everyone of the importance of taking steps to prevent mosquito bites.

“While most people exposed to WNV will not develop serious illness, some may develop very severe illness requiring hospitalization. In some cases, the disease can be fatal.”

The first human case of West Nile virus in the commonwealth this year was confirmed last week in a male patient in his 90s who was exposed in Middlesex County, and on Monday, another Middlesex County resident — a man in his 60s — also tested positive for WNV. Meanwhile, state health officials also recently announced that Eastern equine encephalitis (EEE) — another rare but serious and potentially fatal mosquito-borne illness — had been detected in mosquito samples for the first time this summer.

The samples were collected in the town of Kingston on August 17, and as a result, the risk level for EEE has been elevated to moderate in that community as well as the surrounding towns of Carver, Halifax and Plympton.

So far this year, there have been no documented human or animal cases of EEE, which tends to occur in outbreak cycles, according to State Epidemiologist Dr. Catherine Brown. The last outbreak was seen in 2024, with a total of four human cases and one death reported. There were no documented cases in any of the previous three summers (2021-23), but there was a notable spike in 2019-20, with a total of 17 human cases and seven deaths recorded in that span.

“When EEE is found in mosquitoes later in the season like this, there is less opportunity for the risk to increase to very high levels,” said Brown, “but anytime EEE virus is in mosquitoes, it can be spread to people. We rely on our mosquito surveillance program to monitor for the presence of virus to let people know when and where the risk is occurring so they can take steps to protect themselves.”

Brown said mosquitoes will remain a threat until the first hard frost and urged residents to take some basic precautions to protect themselves and their loved ones, including:

* Applying insect repellent with an EPA-registered ingredient (DEET, permethrin, picaridin, oil of lemon eucalyptus) when spending time outdoors.

* Wearing long sleeves, long pants and socks when outdoors to keep mosquitoes away from your skin and prevent them from biting.

* Being mindful of peak biting times for mosquitoes — dusk to dawn — and consider rescheduling outdoor activities that occur during evening or early morning in areas of high risk.

Homeowners should also take steps to mosquito-proof their home, such as:

* Draining or discarding items that hold water, as mosquitoes lay their eggs in standing water. Be sure to check rain gutters and drains; empty unused flowerpots and wading pools; and change the water in birdbaths frequently.

* Ensuring that window screens are tightly fitted and are free of holes.

Animal owners can also reduce potential mosquito breeding sites on their property by eliminating standing water from containers — especially after heavy rains — and flushing out water troughs at least once a week during the summer months. Horses should be kept in indoor stalls at night to reduce their risk of exposure, and owners should speak with their veterinarian about animal-safe mosquito repellents and vaccinations to prevent WNV and EEE. If an animal is suspected of having either illness, owners are required to report it to both DPH (617-983-6800) and the Division of Animal Health (617-626-1795).

For more information on mosquito-borne illnesses, including prevention tips and the latest WNV and EEE risk maps, visit mass.gov/dph/mosquito.

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