A Massachusetts town is closing its public parks and fields at night after a horse tested positive for eastern equine encephalitis, a rare but lethal mosquito-borne disease.

Eastern equine encephalitis, or EEE, is a potentially fatal virus that is usually spread to humans through the bite of an infected mosquito. The disease is rare, with an average of 11 human cases reported annually, according to the Centers for Disease Control and Prevention.

New measures in the coastal town of Plymouth, about 40 miles southeast of Boston, come after mosquitoes in the area tested positive for EEE and the state reported its first human case of the virus since 2020.

“As (the Massachusetts Department of Public Health) has now elevated 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 risk to exposure to EEE,” said Michelle Bratti, Plymouth Commissioner of Health and Human Services.

While EEE is rare, roughly 30% of cases end in death, and many survivors have ongoing neurologic issues, according to the CDC, and the virus is most common around Eastern or Gulf Coast states. Researchers have also warned that climate change is giving rise to mosquitos as they thrive in warm, humid weather.

Massachusetts towns ring alarm bells on rare but lethal virus

In Plymouth, Massachusetts, where mosquitos have tested positive for EEE, officials announced on Friday it was closing public parks and fields from dusk to dawn when mosquitoes are most active. The town manager also noted public parks, fields, and schools will be sprayed in the coming days.

A wave of precautions against the mosquito-borne virus in Massachusetts comes five years after the state’s most recent outbreak began in 2019, which included 12 cases and six deaths. The state’s Department of Public Health said the outbreak continued into 2020 which saw five reported cases and one fatality. Massachusetts experiences an outbreak of EEE every 10 to 20 years, and it lasts two to three years, according to the agency.

Earlier this month, a man in his 80s tested positive for EEE — Massachusetts' first case since 2020 — causing the state's health department to raise risk levels for about a dozen nearby towns. Officials did not name the person but said he was infected in Worcester County.

In Oxford, a town in Worcester County, the local Board of Health unanimously voted to recommend that outdoor events end at 6 p.m. through September, and 5 p.m. starting in October through the first hard frost.

Rike Sterrett, Oxford's director of public health, stressed the move is a recommendation, not a mandate while adding that all town-sponsored activities will follow the curfew. She noted the recommendation has received some pushback from families with children who play school sports as games and practice times could be impacted.

Officials urge caution after non-human cases in other states

Officials in New York urge caution against the mosquito-borne disease after two horses in the state tested positive: one in Galen and another in Newburgh. The horse cases usually indicate mosquitoes in the area carry the virus.

Sample testing of mosquitoes in Rhode Island, Connecticut, and Massachusetts have also turned up positive for EEE, as officials urge residents to schedule outdoor activities outside of dusk to dawn. The CDC has tracked three human cases this year – one each in Massachusetts, Vermont, and New Jersey.

How to protect yourself from EEE

Eastern equine encephalitis is spread to humans through bites from infected mosquitos. The virus can cause a fever, headache, vomiting, diarrhea, seizures, behavioral changes, and drowsiness, according to the CDC.

Most people infected with easter equine encephalitis do not develop symptoms, the CDC said. People of all ages are susceptible to infection, but people over 50 and younger than 15 are at greatest risk.

There is no treatment or vaccine for EEE, but people in high-risk areas can protect themselves by preventing mosquito bites, which are most likely to happen from dusk to dawn. Take precautions to avoid mosquito bites and protect against potential exposure to the mosquito-borne illness:

• Use insect repellent
• Wear loose-fitting, long-sleeved shirts and pants
• Use air conditioning and window screens to prevent mosquito bites indoors
• Dump out containers of water near your home to eliminate breeding grounds

Contributing: Mike Murphy, Rochester Democrat and Chronicle, Henry Schwan, Telegram and Gazette