A rare but serious illness spread by mosquitoes has led one town in Massachusetts to close its parks and fields each evening. Four other towns are also advising residents to stay indoors after dark.

The illness in question is eastern equine encephalitis (EEE). State health officials revealed last week that a man in his 80s had contracted the disease, marking the first reported human case in Massachusetts since 2020.

Plymouth, a town located about 40 miles (64 kilometers) southeast of Boston, announced on Friday that all public outdoor recreational areas will be closed from dusk until dawn. This decision comes after a horse in the town was found to be infected with EEE.

In addition, state health officials have issued warnings for a group of four towns south of Worcester—Douglas, Oxford, Sutton, and Webster—where there is a “critical risk” following the infection of a man from Oxford.

Health officials are advising residents in these areas to complete outdoor activities by 6 p.m. until September 30, and by 5 p.m. after that, until the first hard frost. They also recommend that everyone in Massachusetts use mosquito repellent when outside and eliminate any standing water around their homes, as this can breed mosquitoes.

Jennifer Callahan, the town manager of Oxford, shared in a memo that the family of the infected man reached out to her office seeking to raise awareness. “They want people to understand that this is a very serious disease with severe physical and emotional effects, regardless of whether the person survives,” Callahan stated.

The infected man had previously told his family that he rarely got bitten by mosquitoes. However, just before showing symptoms, he mentioned that he had been bitten. Currently, he remains in the hospital and is “courageously battling” the virus.

Callahan emphasized that the man’s family is urging everyone to take public health recommendations seriously and to do their best to protect themselves.

The presence of the EEE virus was confirmed last month in a sample taken from mosquitoes in Massachusetts, and additional cases have since been detected statewide. During a 2019 outbreak, there were six deaths among 12 confirmed cases in Massachusetts, with the outbreak continuing into the following year, resulting in five more cases and another death. Unfortunately, there are no vaccines or effective treatments available for EEE.

The U.S. Centers for Disease Control and Prevention (CDC) states that while EEE is rare, it is extremely serious, with approximately 30% of infected individuals dying from the disease. Symptoms may include fever, headache, vomiting, diarrhea, and seizures. Those who survive often face permanent disabilities, and full recovery is uncommon, according to Massachusetts health authorities. The disease primarily affects birds, and while humans and some mammals can contract EEE, they do not spread the virus.

The CDC reports that only a few cases of EEE are documented in the U.S. each year, with most infections occurring in the eastern and Gulf Coast states.