Press Release  State health officials announce third horse case of EEE in Massachusetts

Boston — The Massachusetts Department of Public Health (DPH) today announced a third confirmed case of Eastern equine encephalitis (EEE) in a horse this year. The horse was exposed to EEE in Carver, an area already at high risk for EEE.

There are no additional risk level changes associated with this finding. In addition to Carver, neighboring Middleborough and Plymouth also remain at high risk for EEE at this time.

"This latest animal case of EEE confirms that even this late in the season, the risk for spread of EEE virus from infected mosquitoes is still present," said Public Health Commissioner Robbie Goldstein, MD, PhD. "With more people going outside to enjoy the mild fall weather, we continue to recommend that residents take steps to protect themselves from mosquito bites until the first hard frost."

There have been 96 EEE-positive mosquito samples in Massachusetts this year. Infected mosquitoes have been found in Barnstable, Bristol, Essex, Norfolk, Middlesex, Plymouth, and Worcester counties. There have been four human cases of EEE in Massachusetts this year, in addition to the three horse cases.

EEE is a rare but serious and potentially fatal disease that can affect people of all ages. EEE is transmitted to humans through the bite of an infected mosquito. The last outbreak of EEE in Massachusetts occurred in 2019-2020 and resulted in 17 human cases with seven deaths and nine animal cases (eight horses and one goat). There were no human or animal cases of EEE in Massachusetts in 2021, 2022, or 2023.

“Cooler temperatures will start to reduce mosquito activity, but people shouldn’t let their guard down yet,” said State Epidemiologist Dr. Catherine M. Brown. “We continue to strongly advise that everyone in areas at high and critical risk for EEE reschedule evening outdoor activities to avoid peak mosquito biting hours.”

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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