A Rare Mosquito-Borne Illness Is On The Rise. Here’s What To Know.

Residents of several New England states are on high alert after officials urged folks to take extra precautions as cases of eastern equine encephalitis, a rare yet deadly mosquito-borne illness, are on the rise.

The number of reported infections overall is low, but it’s still concerning: Notably, a person in New Hampshire has died of the illness. One person in Vermont has also been infected, marking the first human case in the state since 2012, and one person in Massachusetts has been infected, which is the first case in a person in Massachusetts since 2020.

How worried do you need to be? Here’s what experts want you to know:

“Eastern equine encephalitis, or EEE as we often call it, is a mosquito-borne viral infection … that typically is found in bird populations, and it’s transmitted among birds by a particular mosquito that only feeds on birds,” explained Dr. Daniel R. Kuritzkes, the chief of the division of infectious diseases at Brigham and Women’s Hospital in Boston. “But, there are other mosquitoes that feed on both birds and humans and other mammals, and that’s how the infection occasionally spills into the human population.”

“If bitten by an infected mosquito, some people will become sick but others might not even notice,” said Dr. Matthew M. Ippolito, an assistant professor of medicine in the division of infectious diseases at Johns Hopkins School of Medicine in Baltimore.

“Usually about a week after getting bitten a person might start to have flu-like symptoms of fevers, headaches and nausea,” Ippolito added. For many people, this is where the virus stops, although it can sometimes cause lifelong physical and mental issues.

Ippolito said only a small percentage of individuals ― “about 2% of infected adults and 6% of infected children” ― will then go on to develop encephalitis, which is brain inflammation. Signs of encephalitis include a high fever, confusion and vomiting.

Encephalitis is ultimately what may cause a patient to die. Roughly 30% of people infected with EEE die, according to the Centers for Disease Control and Prevention. EEE is most severe in people over 50 and under 15, and it does not spread from person to person.

EEE tends to show up in certain parts of the country. It’s “a viral disease spread by a variety of different mosquitoes that peaks in August to September,” said Ippolito. “Cases have tended to cluster around the Gulf area and Atlantic seaboard but cases have always been known to occur in northern states.”

Currently, the known U.S. cases are clustered in the Northeast — Massachusetts, Vermont and New Hampshire — and Kuritzkes said EEE tends to be most common in this region.

First, don’t panic. This is a rare illness. The CDC says roughly 11 cases are reported throughout the country each year.

Plus, many local health departments track the number of mosquitoes and birds that test positive for EEE, along with horses that become infected and die, according to Kuritzkes.

“It’s usually apparent where the infection is being transmitted,” Kuritzkes explained. Affected counties then spray in order to reduce the mosquito population, which is currently happening in certain parts of Massachusetts.

Not every mosquito carries this virus, either. So the vast majority of bug bites are harmless.

“It will be a rare event for a person to encounter an infected mosquito in the first place, and if you are unlucky enough to get bitten by a virus-infected mosquito, there is still only about a 5% chance, or even less, that you would develop encephalitis,” Ippolito said.

Mosquitoes carry a range of dangerous illnesses in addition to EEE, like West Nile virus. That makes it important to reduce your likelihood of getting a bite ― whether EEE poses a current risk or not.

Kuritzkes said you should “reduce the opportunity for mosquitoes to breed” by eliminating areas in your home with standing water. For example, if you have water basins outside, make sure you regularly dump them.

“And then, in addition ― and somewhat more practically ― is to use personal protection in the way of insect repellents. So, DEET sprayed on the skin, wearing long pants and long-sleeved shirts,” Kuritzkes said.

You should also be mindful of the time of day that you’re outside.

“The mosquitoes that transmit EEE are principally active from dusk to dawn, so trying not to be outdoors unless you’re wearing long sleeves and using insect repellent during those hours will minimize the likelihood of your getting bitten by the mosquitoes,” Kuritzkes suggested.

“You can also avoid areas where the types of birds and mosquitoes that transmit EEE are known to inhabit — EEE typically occurs in and around freshwater hardwood swamps,” Ippolito added.

Experts say you should always be cautious about all mosquito-borne illnesses (and, for that matter, tick-borne illnesses, which also peak in the summer), but also don’t need to worry too much right now.

“There’s good reasons to protect yourself from mosquito bites and tick bites that go beyond EEE, but I don’t think the average person has to be overly concerned about EEE,” Kuritzkes said.