Four towns in central Massachusetts are advising residents to stay indoors at night to avoid contracting a rare but potentially deadly mosquito-borne virus.

State officials didn’t report how the current patient, a man in his 80s in Worcester County, was exposed to the virus or the details of his current condition.

The disease, described by the public health department as “rare but serious,” is caused by a virus transmitted through mosquito bites. Symptoms typically appear five to 10 days after being bitten by an infected mosquito and include high fever, stiff neck, headache, and fatigue.

There are no vaccines to prevent or medicines to treat EEE. In 2019, 12 Massachusetts residents contracted EEE, resulting in six deaths.

“EEE is a rare but serious disease and a public health concern,” said Massachusetts Public Health Commissioner Dr. Robbie Goldstein. “We want to remind residents of the need to protect themselves from mosquito bites, especially in areas of the state where we are seeing EEE activity.”

Specifically, they advise finishing outdoor activities before 6 p.m. through September and 5 p.m. thereafter until the first hard frost. While outside, residents are recommended to use a repellent and wear clothing that reduces skin exposure, such as long sleeves and socks.

At home, residents are recommended to drain or discard items that collect water, such as buckets, tires, flowerpots, and birdbaths, to prevent mosquitoes from breeding in standing water. They are also reminded to install or repair window screens.

There is no enforcement for those who do not comply with the recommendations, according to town officials.

In Oxford, a 6 p.m. curfew is in place for outdoor activities on town property, and people must show proof of insurance and sign an indemnification form before they can use town fields during those hours.

Nationwide, an average of 11 cases of EEE infections are reported each year, mostly in Eastern or Gulf Coast states, according to the Centers for Disease Control and Prevention (CDC).

Humans and other animals that contract the virus are considered “dead-end hosts,” which means there is no subsequent human-to-human, animal-to-human, or human-to-animal transmission.

Many people who recover from EEE are left with long-term physical or mental problems, according to the CDC. These can range from mild to severe intellectual disability, personality disorders, seizures, paralysis, and cranial nerve dysfunction. Survivors with severe disease and ongoing disabilities often require long-term care and die within a few years.