A rare, potentially deadly mosquito-borne disease has sparked concern in the Northeastern U.S.

Last week, a man from Hampstead, New Hampshire, died after testing positive for Eastern equine encephalitis (EEE).

The man “was hospitalized due to severe central nervous system disease, and has passed away due to [the] illness,” according to a statement from the New Hampshire Department of Health and Human Services (DHHS).

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Another New Hampshire man, Joe Casey, is currently in the ICU on a ventilator after contracting three mosquito-borne illnesses, including EEE, according to local reports.

In late August, four Massachusetts towns — Douglas, Oxford, Sutton and Webster — set a voluntary evening lockdown in an attempt to curb the spread of the virus.

That decision came after the Massachusetts Department of Public Health (DPH) confirmed the first human case of Eastern equine encephalitis (EEE) since 2020 in Worcester County, affecting an elderly man in Oxford.

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As of Aug. 27, the Centers for Disease Control and Prevention (CDC) has reported four total cases of the virus in 2024, although that data is subject to change.

There were seven cases reported in 2023, one case in 2022, five in 2021 and 13 in 2020.

The year 2019 saw a spike, with 38 cases reported.

What is Eastern equine encephalitis?

Eastern equine encephalitis is caused by a virus that is spread through the bite of an infected mosquito, according to the CDC, which describes EEE as a “rare but serious disease.”

Only a few cases are reported in the U.S. each year, most in the Eastern or Gulf Coast states.

Humans and other animals that contract the virus are considered “dead-end hosts,” the CDC states, which means they can’t spread it to mosquitoes that bite them.

“While EEE is widespread in the Western Hemisphere, it normally affects animals such as large mammals, birds, reptiles and amphibians, and rarely causes clinical infection in human beings,” Dr. Eyal Leshem, director of the Center for Travel Medicine and Tropical Diseases at Sheba Medical Center in Israel, told Fox News Digital.

What’s causing the uptick?

While EEE was previously “very uncommon” in the U.S., there is the potential for these types of viruses to become more prevalent across the country, according to Dr. Edward Liu, chief of infectious diseases at Hackensack Meridian Jersey Shore University Medical Center.

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“As warm seasons get longer, mosquitoes have more time to breed,” Liu told Fox News Digital. 

“If heavy rains cause standing pools of water, that will create an environment for larger mosquito populations.”

Dr. Marc Siegel, senior medical analyst for Fox News and clinical professor of medicine at NYU Langone Medical Center, confirmed that the virus has been “exceedingly rare, though “frequently disabling (neurologically) and deadly.”

He also told Fox News Digital, “I don’t think it will become a problem, as it is very rare, with just a few cases per year, but the fear of it is spreading.”

Symptoms of the virus

Common symptoms of EEE include fever, vomiting, diarrhea, headache, stiff neck, seizures, behavioral changes and drowsiness, per the CDC.

These usually appear five to 10 days after being bitten.

The disease can be deadly, resulting in fatalities for 30% of infected people.

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“Sometimes patients exhibit a change in mental status or other neurological symptoms, which are linked to inflammation in their meninges (membranes that protect the brain and spinal cord) or their brains,” said Leshem. 

“There is no specific drug or antiviral that has proven effective in treating EEE.”

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Older people and those who are immunocompromised are at the highest risk for mosquito-borne encephalitis.

The disease is also more dangerous if it occurs in tandem with other viral infections that cause encephalitis, according to Liu.

“We know ticks can carry more than one pathogen, so it would be concerning if mosquitoes carry more than one pathogen,” he said.

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The only treatment for EEE is supportive care to manage symptoms.

“There is no specific drug or antiviral that has proven effective in treating EEE,” Leshem said. 

There is also no vaccine available for Eastern equine encephalitis. 

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“Testing for encephalitis is still not very available outside of hospitals, and sometimes not accurate,” Liu warned.  

“It would not be surprising if its testing confused two similar viruses, as the antibody testing we use is not always accurate.”

Preventing infection

Protecting against mosquito bites is the best way to prevent infection, experts agree.

“We need to make sure that mosquito control programs stay strong,” said Liu.  

“We cannot rely on each homeowner to pay for mosquito control services. In New Jersey, mosquito control is county-based and therefore at the mercy of the county budget.”

“Testing for encephalitis is still not very available outside of hospitals, and sometimes not accurate.”

The CDC recommends using insect repellent, wearing long-sleeved shirts and pants, and treating clothing and gear with permethrin, which is an insecticide that kills or repels mosquitoes.

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Taking steps to control mosquitoes indoors and outdoors can also help prevent infection, the agency states on its website.

Some recommended strategies include using screens on windows and doors, using air conditioning when possible, and eliminating standing water where mosquitoes tend to lay their eggs.