Press Release  State health officials announce additional human cases of EEE and West Nile Virus

Boston — The Massachusetts Department of Public Health (DPH) today announced one additional human case of Eastern equine encephalitis (EEE) and one additional human case of West Nile virus (WNV) in Massachusetts this year.

Both cases are men in their 70s. One man was exposed to EEE in central Middlesex County, bringing the total number of EEE cases in Massachusetts this year to three. The other man was exposed to WNV in southern Middlesex County in an area already at high risk for the disease. This is the seventh case of WNV in Massachusetts this year.

As a result, EEE risk levels are being raised to high in Acton, Ayer, Boxborough, Carlisle, and Littleton in Middlesex County; and Harvard in Worcester County. The following communities are being raised to moderate: Bedford, Billerica, Chelmsford, Concord, Framingham, Groton, Lincoln, Shirley, Stow, Tyngsborough, Wayland, and Westford in Middlesex County; and Berlin, Bolton, Clinton, and Lancaster in Worcester County.

WNV risk levels in the following communities are being raised to high: Stoneham and Wakefield in Middlesex County.

“Today’s announcement of additional West Nile virus and Eastern equine encephalitis cases makes it clear that mosquito season is not over,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “It is essential that residents continue to use mosquito repellent with an EPA-registered active ingredient every time they are outdoors. We also strongly recommend that residents and towns in areas at high risk for EEE reschedule their evening outdoor events to avoid peak mosquito biting hours.”

There have been 88 EEE-positive mosquito samples in Massachusetts this year. While most activity has been focused in Plymouth and Worcester counties, infected mosquitoes have also been found in Bristol, Essex, and Middlesex counties. There have been 299 WNV-positive mosquito samples so far this year detected from Barnstable, Berkshire, Bristol, Dukes, Essex, Franklin, Hampden, Middlesex, Norfolk, Plymouth, Suffolk, and Worcester counties.

EEE and WNV are transmitted to humans through the bite of an infected mosquito. The last outbreak of EEE occurred in 2019-2020 and resulted in 17 human cases with seven deaths. There were six human cases of WNV and no animal cases in 2023. No animal cases of WNV have been detected so far this year.

“Mosquito behavior starts to change in September,” said State Epidemiologist Dr. Catherine Brown. “They will be less active during cooler temperatures. However, during periods of warmer weather, such as are being forecast for the end of next week, mosquitoes will be out and looking for their next meal.”

People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes.

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), or 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.

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 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 draining or discarding items that hold water. Check rain gutters and drains. Empty 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 windows and doors.

Protect Your Animals

Animal owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools – especially after heavy rains. Water troughs provide excellent mosquito breeding habitats and should be flushed out to reduce mosquitoes near paddock areas. Horse owners should keep horses in indoor stalls at night to reduce their risk of exposure to mosquitoes. Owners should also speak with their veterinarian about mosquito repellents approved for use in animals and vaccinations to prevent West Nile virus (WNV) and EEE. 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 by calling 617-626-1795, and to the Department of Public Health by calling 617-983-6800.

More information, including all WNV and EEE positive results, can be found on the Arbovirus Surveillance Information web page at Mosquito-borne Diseases | Mass.gov, which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800.

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