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Image via Canva. Pictured are mosquito larvae in water, with an inset photo of an adult mosquito.
8-20-2026 10:30am
Massachusetts Reports Season’s First Human WNV Case, First EEE-Positive Sample
Darlene Cancell
Editor
On Thursday, August 20, the Massachusetts Department of Public Health (DPH) announced the state’s first human case of West Nile virus (WNV) this year and is urging residents to take necessary precautions to avoid mosquito bites. The announcement comes one day after DPH reported that Eastern equine encephalitis (EEE) virus had been detected in mosquitoes in Massachusetts for the first time this year.
WNV and EEE are generally spread to people through the bite of an infected mosquito. While some people infected with WNV or EEE may experience no symptoms, others can develop serious and potentially fatal illnesses.
“The mosquitoes will be with us until the first hard frost,” said State Epidemiologist Dr. Catherine M. Brown. “People should use mosquito repellent with an EPA-registered active ingredient, clothing to reduce exposed skin, and consider rescheduling outdoor activities that occur during the evening or early morning when mosquitoes are most active.”
West Nile Virus Detected in Middlesex County Resident and Westwood Area Mosquito Samples
The first human case of WNV in Massachusetts this year involves a man in his 90s who was exposed in Middlesex County.
Due to this finding, along with 180 WNV-positive samples detected in 13 counties, DPH has elevated WNV risk levels to moderate in 70 communities, including Westwood and surrounding communities.
According to DPH’s website, a moderate risk level means that infection with WNV is likely or has already occurred in the designated area. Norfolk County communities that have a moderate risk level as of the publication of this article are Avon, Bellingham, Brookline, Canton, Cohasset, Dedham, Dover, Franklin, Holbrook, Medfield, Needham, Norfolk, Norwood, Sharon, Stoughton, Walpole, Wellesley, Westwood, and Wrentham.
“West Nile virus can be a devastating disease, especially for those who are older or have compromised immune systems. This first case in Massachusetts should remind people across the state that risk remains high,” said Public Health Commissioner Robbie Goldstein, MD, PhD.
West Nile virus (WNV) was detected in Westwood, Dover, and Dedham in late July this year. Positive WNV samples were also found in the neighboring town of Dedham on June 24 and in nearby Brookline on July 15.
“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,” said Dr. Goldstein. “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,” he said.
Eastern Equine Encephalitis Detected in Mosquitoes
On August 19, DPH announced the presence of EEE in Massachusetts in mosquito samples collected on August 17 in the town of Kingston in Plymouth County. The finding has resulted in DPH elevating the risk level of EEE to moderate in the communities of Carver, Halifax, Kingston, and Plympton.
“EEE activity in Massachusetts tends to occur in outbreak cycles,” said State Epidemiologist Dr. Catherine M. Brown. “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. But anytime EEE virus is in mosquitoes, it can be spread to people.”
As of August 20, according to the health department's database and map of EEE risk levels, the risk of EEE remains low in Westwood and all areas of Massachusetts except for the four named communities.
There were 12 human cases of EEE in Massachusetts in 2019 resulting in six deaths. In 2020, there were five human cases and one death. In 2024, there were four human cases and one death. DPH notes that there were no human cases of EEE in Massachusetts in 2021, 2022, 2023, or 2025.
Tips to Protect Against WNV and EEE
State officials say residents have an important role to play in protecting themselves and their loved ones. Residents can take the following actions to avoid mosquito bites:
- Apply Insect Repellent when Outdoors. Use a repellent with an EPA-registered ingredient such as DEET (N,N-Diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus (p-menthane-3,8-diol (PMD) or IR3535), according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30 percent or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.
- Protection for Young Children. Use mosquito netting on baby carriages and playpens.
- Be Aware of Peak Mosquito Hours. The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during the evening or early morning in areas of high risk.
- Clothing Can Help Reduce Mosquito Bites. Wearing long sleeves, long pants, and socks when outdoors will help keep mosquitoes away from your skin.
- Mosquito-Proof Your Home.
- Drain Standing Water. Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by either draining or discarding items that hold water. Check rain gutters and drains. Empty any unused flowerpots and wading pools and change the water in birdbaths frequently.
- Install or Repair Screens. Keep mosquitoes outside by having tightly fitting screens on all your windows and doors.
- Protection for Animals.
- Eliminate breeding sites. Empty standing water in containers around your property. Buckets, tires, and wading pools should be emptied, especially after heavy rains. Troughs should be flushed out at least once a week during the summer months to reduce mosquitoes near paddocks.
- Keep horses in indoor stalls at night. Along with horses, llamas, alpacas, and some birds are known to be susceptible to EEE.
- Speak with your veterinarian. Ask about mosquito repellents approved for use on animals and vaccinations to prevent WNV and EEE.
- Report suspected cases. If an animal is suspected of having WNV or EEE, owners are required to report the suspected case to the Department of Agricultural Resources, Division of Animal Health by calling 617-626-1795, and to the Department of Public Health by calling 617-983-6800.
- While it is possible for dogs and cats to become infected by WNV or EEE, the health department says these infections are very rare. If infected, most dogs and cats fully recover from the viruses.
More information, including all WNV and EEE-positive results, can be found on the Arbovirus Surveillance Information web page, which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800.
"The Department of Public Health recommends that people use mosquito repellent when they are spending time outdoors so they can enjoy the rest of the summer and decrease their risk of being bitten," Dr. Goldstein said.
