What to know about the mosquito virus spreading through New England

A rare and dangerous mosquito-borne illness is spreading through New England, putting states on high alert with one death already confirmed following an infection. 

Cases of eastern equine encephalitis (EEE) have been detected in at least five states this year: Massachusetts, Vermont, Wisconsin, New Jersey and New Hampshire.  

The Massachusetts Department of Public Health warned last weekend that 10 communities in the state are at high or critical risk for the EEE virus. A New Hampshire resident was confirmed to have died this week after testing positive for EEE. 

EEE, or “triple E,” is spread through the bite of infected mosquitoes. There are no vaccines or treatments available for the virus. The mosquito-borne disease occurs rarely in the U.S., but it can be deadly. 

Here’s what we know.

It’s a rare coastal disease 

As can be expected for a disease spread through mosquitos, EEE largely occurs in coastal regions of the U.S. such as New England and New Orleans. 

“Definitely, I'd say New England and the Gulf Coast are the two areas in the U.S. where it's mainly occurred in the past,” said Dr. David Hamer, professor of global health and medicine at the Boston University School of Public Health. 

“Massachusetts has had hundreds of cases over a 70-year period,” Hamer added. “There may not be any for a couple years, and then there's another case or two, although we believe that it may be occurring a little more frequently.” 

Factors like increased travel and a warmer planet may potentially be contributing to higher incidences of mosquito-borne illnesses like EEE, Zika, dengue and malaria. 

The Centers for Disease Control and Prevention (CDC) said the U.S. usually sees somewhere between three and 15 EEE cases per year with an average of seven cases nationally per year. In 2023, seven cases were reported.

Cases tend to peak between July and September. 

“CDC is in touch with impacted states and has offered support. We encourage Americans to listen to the guidance of their state and local health officials,” the agency said in a statement. “While EEE infections are rare, this is not a new virus, and CDC has monitored the sporadic infections in the U.S. for years.” 

Most don’t know they’re infected 

According to Ruanne Barnabas, chief of the Division of Infectious Diseases at Massachusetts General Hospital, most people who get infected with EEE are unaware and asymptomatic. 

“In 95 percent of cases, the infection has no symptoms at all, and the person is really quite well and doesn't know they have the virus,” Barnabas said.  

“But in 5 percent of cases, people do have symptoms, including fever, chills. And then it can actually affect the central nervous system, and they can develop confusion, abnormal movements and encephalitis as well. And in those cases, about a third of cases do result in in death.” 

When reached for more information by The Hill, the CDC said it was currently unaware of any EEE deaths other than the one confirmed in New Hampshire this week. 

Infections can be severe and life altering 

The minority of people who develop severe symptoms of EEE can experience flu-like effects such as fever, aches, joint pain and chills. More severe effects include neurological symptoms such as meningitis and the namesake encephalitis, an inflammation of the brain. 

Most people will experience asymptomatic infections, but the disease kills about 30 percent of those who develop severe symptoms. According to the CDC, about half of those who survive a severe EEE infection experience long-term complications. 

Infections typically last one to two weeks but long-lasting side effects are possible. The CDC lists intellectual disability, personality disorders, seizures, paralysis and cranial nerve dysfunction among the potential long-term effects of an EEE infection. 

There are no vaccines or treatments for EEE and caring for an infection largely involves supportive care to reduce the severity of symptoms. 

“There's a lot of supportive medical care that can help reduce the sort of inflammation associated with encephalitis,” Hamer said. “So, there may be things that can be done in the hospital or the ICU that can reduce risk of dying, but also complications developing.” 

Risk factors unclear 

Unlike other diseases spread by mosquitoes, it’s unknown whether certain groups are at a higher risk of severe illness from EEE.  

The West Nile virus is believed to impact seniors and immunocompromised individuals more severely. Young children under 5 years of age; pregnant women; and people with HIV or AIDS are believed to be more severely impacted by malaria. 

But EEE seems to impact different groups the same. 

“If you look at the cases, it seems to hit, you know, young teenagers, 30-year-olds, 40-year-olds — I mean healthy people that don't have clear risk factors. And so, I think for Eastern equine, everybody needs to be cautious,” Hamer said. 

The New Hampshire man who died after contracting EEE was 41 and healthy with no underlying conditions, according to his family. 

Avoiding infections 

While rare, avoiding EEE infections is the same as avoiding other mosquito diseases. 

“Wear long sleeves. If you have any standing water and pots and things, turn those pots over and remove the standing water,” Barnabas said, adding that the first frost of the year should kill off any remaining mosquitos later this year. 

The CDC’s recommended insect repellants for preventing mosquito bites include DEET, picaridin, IR3535, oil of lemon eucalyptus, Para-menthane-diol and 2-undecanone.  

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