A New Hampshire man has died of eastern equine encephalitis, also called EEE, prompting questions about the rare mosquito-borne disease.

The 41-year-old was hospitalized due to severe central nervous system disease and died within a week. He was healthy and had no underlying conditions.

Eastern equine encephalitis is “exceedingly rare,” Dr. Céline Gounder, CBS News medical contributor and editor-at-large for public health at KFF Health News, said on “CBS Mornings” Wednesday.

“I only saw one case, that was about 20 years ago in Massachusetts, and most providers will never see a case of ‘Triple E,’ as we call it,” she said.

The virus typically spreads in certain swamps, including red maple and white cedar swamps in Massachusetts, and experts think horses may be a host animal, hence the word “equine” in the name.

“This is something that we see with many infectious diseases — that the host might be another animal, maybe a bat, which is what we suspect with COVID, for example, or with Ebola,” Gounder said. “But in this case, what we think is happening is horses, perhaps other animals are the host. Mosquitoes are biting them and then transmitting that infection to humans.”

There have been three additional cases of eastern equine encephalitis in the U.S. this year, according to the U.S. Centers for Disease Control and Prevention, one each in New Jersey, Vermont and Wisconsin. 

CDC Director Mandy Cohen warned that a warming climate is also affecting these kinds of outbreaks. 

“The impact of heat on our health and climate change is not only impacting us as humans, but it’s changing where mosquitoes and ticks live, and thus what diseases are moving around in different regions. We’re just seeing more bugs, and some of those bugs are becoming resistant to our control methods resistant bugs,” Cohen told CBS News.

EEE symptoms

Most people infected with eastern equine encephalitis don’t develop symptoms, but some can come down with fever or swelling of the brain.

According to the CDC, symptoms can also include: 

• Headache
• Vomiting
• Diarrhea
• Seizures
• Behavioral changes
• Drowsiness

“Approximately 30% of people with eastern equine encephalitis die, and many survivors have ongoing neurologic problems,” the CDC notes.

How to protect against EEE

There are no vaccines to prevent eastern equine encephalitis and no medicines to treat it, so the best way to not get sick is avoiding bug bites.

To do this, experts suggest: 

• Using insect repellent
• Wearing long-sleeved clothing
• Staying indoors when mosquitoes are out
• Draining standing water

People in some areas of Massachusetts have been warned to stay indoors when mosquitoes are most active, typically at dusk and dawn. Authorities in the state are also using trucks and planes to spray vulnerable areas with insecticide.

Controlling mosquitoes is an important step, Gounder said.

“There are some newer technologies there to control mosquitoes that don’t involve pesticides. Some of those are being piloted in place like the Florida Keys, where you have lots of mosquitoes, but we still have a lot to go in terms of developing treatments or vaccines,” she said. 

The Associated Press contributed reporting.