A Rare, Brain-Swelling Virus Has Been Detected in East Coast Mosquitos 

"There is more activity than we typically see." 


In Freetown, Massachusetts, it’s the height of summer. Yet all public spaces in the town just 50 miles from Cape Cod will be closed from dusk until dawn because of a rare mosquito-borne virus that has local public health officials on alert.

In a statement released Wednesday by the Massachusetts Department of Public Health, officials are warning that 92 local mosquito samples have tested positive for a rare but dangerous virus called Eastern equine encephalitis virus (EEEV). In humans, it can cause a type of brain inflammation called Eastern equine encephalitis (EEE). The illness is extremely rare — the CDC notes that an average of only seven cases are reported in the US each year — but it is dangerous. In 30 percent of cases, it can be fatal.

The health risks are part of the reason local officials have put several Massachusetts towns on alert this week. But they’re also raising awareness about the strange behavior of these mosquitos. They’ve shown up a bit earlier than anyone expected them to.

“We’re raising the risk level because there is more activity than we typically see and it is happening early in the season,” said Dr. Monica Bharel, MPH, the Massachusetts public health commissioner.

Massachusetts public health officials are warning several locals towns about mosquitos carrying Eastern equine encephalitis virus.

The alert in Massachusetts comes within a week of a similar announcement in Florida, where public health officials are also warning of EEE infections in several chicken populations. It may seem like a scary coincidence, but EEV cases, as rare as they are, aren’t too out of character for both Massachusetts or Florida.

According to the CDC, between 2009 and 2018 two states had the highest recorded numbers of brain disease caused by EEV. Over nine years, Florida had 13 and Massachusetts had ten.

In rare cases throughout history, EEE has also been detected in New York (eight cases), North Carolina (seven cases) and Georgia (six cases).

As Bharel notes in the release, it is a bit suspect to see these mosquitos around so early in the year, even in Massachusetts. While Massachusetts Public Health doesn’t go into detail as to why that might be happening, there is evidence that the climate crisis is affecting the transmission of other mosquito-borne illnesses.

EEE cases in humans between 2009 and 2018, by state. 


A paper published in March in PLOS Neglected Tropical Diseases showed that dengue fever and other serious mosquito-borne illnesses may affect up to 1 billion more people in 2080 than they do right now due to warming temperatures.

In a previous interview with Inverse, study author Colin Carlson, Ph.D., a post-doc at Georgetown University, said his findings were “extremely concerning, and almost certainly means more people getting sick globally.”

His study, however, focused not on EEE but on malaria, zika, dengue, and yellow fever, which already cause millions of deaths per year in tropical climes.

It may not be too much of a stretch to suggest that it may also impact the spread of mosquitos carrying EEEV in the future (if it isn’t already.) — though importantly, neither public health department has made the connection. What they’re focused on is helping people prevent infection.

This comes down to preventing mosquito bites themselves, which people can do by wearing protective clothing, applying an EPA-approved mosquito repellant, and, like the town of Freeport, staying indoors during dusk and dawn hours, when the mosquitos tend to be most active. The Massachusetts Department of Public Health is also advising people to make sure that they install screens in their windows and drain pools of standing water, where mosquitos might congregate.

The extra precautions are absolutely worth taking in light of the risks that EEE can pose.

The EEE-bearing mosquitos are another summer public health concern Americans have to watch out for in 2019, in addition to the threat of flesh-eating bacteria. But fortunately, in both cases, there are straightforward things that can be done to help protect yourself.

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