Massachusetts Records Human Case of Eastern Equine Encephalitis


In total, 24 Massachusetts communities are now considered high risk for EEE virus and 18 communities have been designated to be at moderate risk.

Health officials with the Massachusetts Department of Public Health have announced a confirmed human case of eastern equine encephalitis (EEE).

EEE virus is transmitted to humans through the bite of an infected mosquito. According to the US Centers for Disease Control and Prevention (CDC), human cases of EEE virus occur infrequently and only 4-5% of human EEE virus infections actually lead to EEE disease.

Infection can result in either systemic or encephalitic illness. Systemic infections consist of an abrupt onset of chills, fever, malaise, arthralgia, and myalgia, which persists for approximately 1 to 2 weeks. In adults, encephalitis can manifest a few days following systemic illness. Encephalitic symptoms include fever, headache, irritability, restlessness, drowsiness, vomiting, diarrhea, convulsions, and coma.

The CDC notes that approximately one-third of patients who progress to the encephalitic stage die. For individuals who recover, many develop mental and physical sequelae which can be debilitating and also lead to death.

Massachusetts health officials indicate that this case—which was diagnosed in a male over the age of 60 years in southern Plymouth County—is the first human case of EEE in the state since 2013. According to the statement, EEE has historically occurred sporadically across the state. The most recent outbreaks of the disease occurred from 2004 through 2006 and 2010 through 2012. During these 2 outbreaks, 22 human cases of EEE were documented, with 14 cases recorded in Bristol and Plymouth counties.

In total, 24 Massachusetts communities are now regarded as high risk for EEE virus and 18 communities have been designated as moderate risk.

According to the CDC, an average of 7 human cases of EEE are documented annually across the United States, with the largest number of cases reported in Florida, Massachusetts, New York, and North Carolina. Transmission is most common in and around “freshwater hardwood swamps,” located in states along the Atlantic and Gulf Coasts and the Great Lakes region.

The Massachusetts Department of Agricultural Resources has announced that mosquito control and monitoring is ongoing in both Bristol and Plymouth counties. These efforts are designed to reduce the risk of EEE in the area, but residents should also use mosquito repellent and try to reduce exposure to mosquitoes. In 2019 alone, the department identified EEE virus in 227 mosquito samples from species that are capable of transmitting the virus to humans.

There is currently no human vaccine to protect against EEE or antiviral treatment available to treat the infection.

“Today’s news is evidence of the significant risk from EEE and we are asking residents to take this risk very seriously,” Monica Bharel, MD, MPH, public health commissioner of Massachusetts, said in the Department of Health’s statement. “We will continue to monitor this situation and the impacted communities.”

Contagion® will continue to provide updates on human EEE cases as they become available.

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