Before 2019, the mosquito-borne disease, eastern equine encephalitis (EEE), only infected 10 people in the United States each year, and fatalities were virtually unheard of in Massachusetts. Unfortunately, this is no longer the case, as an Essex County man was recently declared the fourth EEE fatality in Massachusetts this year, and 11 other residents of the state have contracted the disease from the bites of infected mosquitoes. All four of these fatalities occurred within a one month timeframe, which is highly unusual and has prompted research into the cause of the sudden mosquito-borne disease epidemic in the northeast.

Public health authorities in Massachusetts and neighboring states have been conducting area-wide aerial spraying operations in order to reduce the number of EEE-infected mosquitoes, but the rate of infection has remained steady despite these efforts. Although October is only a few days away, and temperatures in Massachusetts are dropping, mosquitoes remain abundant in urban and suburban areas of the state. At the moment, 46 Massachusetts communities have been declared high risk areas for EEE infection, and 36 communities are at critical risk for EEE infection. Authorities in Massachusetts are enforcing an after dark curfew in order to protect residents from mosquito bites, as the urban mosquito species that can carry EEE become most active during and after dusk. This curfew will stay in effect until the first winter frost arrives and kills off the mosquitoes.

Researchers are not entirely sure why EEE-infected mosquitoes are so abundant in urban and residential areas of Massachusetts this year, but the state epidemiologist in Massachusetts believes that birds migrating to Massachusetts from Florida are the ultimate cause of the EEE outbreak. Typically, only rural-dwelling mosquito species contract EEE by feeding on the blood of infected birds in swampy areas of Massachusetts, but sometimes, urban species feed on the blood of EEE-carrying birds as well. In Florida, the EEE virus has been a major problem for years due to the abundance of EEE-infected birds, and these birds migrate to Massachusetts swamplands each year. Birds eventually develop an immunity to EEE, which prevents mosquitoes from contracting the virus while feeding on their blood. This year, however, a new batch of non-immune Florida birds arrived in Massachusetts, causing a large number of mosquitoes to contract the disease before spreading it to residents. This theory explains why EEE outbreaks tend to occur every 20 years in the northeast.

Are you concerned about contracting EEE from infected mosquitoes?