Rare but deadly mosquito virus worries US cities

A coastal town in Massachusetts is closing its parks, playgrounds and fields from dusk to dawn for fear of the mosquito-borne Eastern Equine Encephalomyelitis (EEE) virus.

Plymouth put the closures into effect on August 23 and advised the public to remain cautious and follow tips on the Massachusetts Department of Public Health (DPH) website. The news comes after state health officials announced on August 16 that a man in his 80s had become infected with electrical and electronic equipment after coming into contact with it in Worcester County – reportedly the first human case in Massachusetts since 2020.

“Now that Mass DPH has raised Plymouth's EEE risk status to high, it is important to take extra precautions when outdoors and follow state and local health guidelines to avoid unnecessary risks of exposure to EEE,” Plymouth Health and Human Services Commissioner Michelle Bratti said in a news release. “The health and safety of our community, residents and visitors remains our priority.”

Worcester County in Massachusetts is also concerned about the mosquito-borne virus. On Saturday, August 24, state officials announced that they would be spraying mosquito repellent in parts of Worcester and Plymouth counties due to electrical and electronic equipment.

Here's what you need to know.

What is Eastern Equine Encephalomyelitis?

According to the Massachusetts DPH, EEE is very rare but incredibly serious. Since the virus – which is transmitted through the bite of an infected mosquito – was first identified in Massachusetts in 1938, just over 115 cases have occurred. Additionally, EEE outbreaks in Massachusetts typically occur every 10 to 20 years.

The City of Plymouth's press release states that according to the Massachusetts Department of Environment and Safety, “the fatality rate for electrical and electronic equipment (EEE) in humans varies from 33% to 70%, with most deaths occurring two to ten days after the onset of symptoms.”

Symptoms may include fever, headache, vomiting, diarrhea, seizures, behavioral changes, and drowsiness. According to the Massachusetts DPH, inflammation and swelling of the brain, called encephalitis, is the most dangerous and most common serious complication of EEE.

EEE can worsen rapidly and some patients may fall into a coma within a week.

Humans and some mammals are so-called dead-end hosts, meaning they do not transmit the virus to mosquitoes that bite them, even if they become sick.

How is Eastern Equine Encephalomyelitis tested and treated?

Electrical and electronic equipment Diagnosis is made based on symptoms and a test of spinal fluid or blood, which can show whether the virus or viral antibodies are present in the body.

There are currently no human vaccines or targeted treatments for EEE. According to the Centers for Disease Control and Prevention (CDC), clinical treatment for the virus is recommended. Patients with EEE need to be closely monitored by their doctor, who may prescribe pain medication or other treatments to manage the specific symptoms of EEE.

Overall, prevention is key. In Plymouth's Aug. 23 notice, the city recommended certain strategies for citizens to avoid mosquito bites, including draining standing water, wearing long sleeves and pants during peak mosquito seasons, and installing screens in your home. They also recommended using insect repellent, specifically a repellent with an EPA-registered ingredient.

Pet owners should reduce potential mosquito breeding grounds on their property by removing standing water from containers such as buckets, tires and wading pools – especially after heavy rains.

Which US cities have raised their electrical and electronic equipment risk level to “critical” or “high”?

Four cities in Massachusetts have raised the risk level for electrical and electronic equipment to “critical”: Douglas, Oxford, Sutton and Webster.

According to the Massachusetts Department of Public Health, in addition to Plymouth, the cities of Carver, Dudley, Middleborough, Northbridge and Uxbridge have raised their risk levels for electrical and electronic equipment to “high.”

West Nile virus, which is transmitted primarily by mosquitoes, is also a growing concern. In July, several local health departments issued warnings to citizens after officials discovered mosquitoes carrying West Nile virus across the U.S. As of August 20, the CDC had recorded 216 cases in 33 states in 2024.

On August 24, it was confirmed that Dr. Anthony Fauci, who served as chief medical adviser to the president from 2021 to 2022, was hospitalized after being infected with the West Nile virus. He is currently recovering at home.