Public Health Officials Announce Season’s First EEE Positive Mosquito Samples

The Massachusetts Department of Public Health (DPH)  announced that Eastern equine encephalitis (EEE) virus has been detected in mosquitoes in Massachusetts for the first time this year. The presence of EEE was confirmed today by the Massachusetts State Public Health Laboratory in mosquito samples collected on August 30 in Douglas and Southbridge in Worcester County. No human or animal cases of EEE have been detected so far this year. 

The finding increases the risk level of EEE to moderate in the communities of Douglas, Dudley, Southbridge, Sturbridge, Uxbridge, and Webster in Worcester County. 

“After the EEE outbreak cycle that occurred in 2019 and 2020, there was no EEE activity in Massachusetts in 2021 or 2022,” said Public Health Commissioner Robert Goldstein, MD, PhD. “This is a late season emergence for EEE which should keep the risk level from rising too much or too quickly. However, some risk from mosquito-borne disease will continue until the first hard frost and people should take steps to prevent mosquito bites.”

EEE is a rare but serious and potentially fatal disease that can affect people of all ages. EEE is generally spread to humans through the bite of an infected mosquito. There were 12 human cases of EEE in Massachusetts in 2019 with six deaths and five human cases with one death in 2020. There were no human cases of EEE in Massachusetts in 2021 or 2022.

“Transmission of EEE to a person late in the season can happen,” said Dr. Catherine M. Brown, State Epidemiologist. “Mosquitoes will be more active during warm and humid weather as we are forecast to have this weekend. I encourage everyone to use mosquito repellent when they are outdoors enjoying the last unofficial weekend of summer; you can also use clothing to cover exposed skin and if you notice that you are getting bitten, you should consider moving indoors.”

 Avoid Mosquito Bites

• Apply Insect Repellent when Outdoors. Use a repellent with an EPA-registered ingredient (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.

• 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 at least once a week during the summer months 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 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 |, which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800.

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