Health authorities have warned residents to protect themselves against bites from mosquitoes that can transmit a rare virus that has killed at least five people in three states this year.

An increase in cases of the disease, called Eastern Equine Encephalitis, has prompted authorities in Michigan, Massachusetts, Connecticut, Rhode Island and New Jersey to issue the warnings: Remove standing water. Use repellent. Seal windows and doors.

The five deaths were in Michigan, Massachusetts and Rhode Island, according to state officials.

In Michigan, three people have died from the disease, for which there is no known vaccine, in a total of seven confirmed cases this year, state officials said this week.

The state is experiencing its worst outbreak of the disease in more than a decade, Joneigh Khaldun, the state’s chief medical executive, said in a statement on Tuesday.

In Massachusetts, there was one fatality in the nine confirmed cases so far this year, state authorities said Wednesday. One person died from the disease out of the three cases in Rhode Island, health authorities in that state reported Tuesday.

“We strongly encourage residents to take precautions such as using insect repellent with DEET, wearing long-sleeved shirts and long pants when outdoors during the peak mosquito-biting hours, which are dusk and dawn,” James Rutherford, a health officer for Kalamazoo County’s Health and Community Services in Michigan, said in a statement earlier this month.

In Michigan, the fatal case was in Kalamazoo County, which is south of Grand Rapids, the statement said. The man who died was identified by his family as Gregg McChesney, 64, a local television station reported.

He was a “perfectly healthy, happy human being and within a matter of nine days he went from perfectly healthy to brain dead,” Mark McChesney, a brother, told News 8 on Tuesday.

On Monday, the authorities in Connecticut announced their first human case of EEE for this season.

The commissioner of the Department of Public Health, Renée D. Coleman-Mitchell, on Monday said an adult in East Lyme has tested positive for the disease after falling ill during the last week of August with encephalitis, and is in the hospital, said the Connecticut Department of Public Health statement.

“Other states throughout the Northeast are also experiencing an active season for EEE,” the statement said.

New Jersey’s Department of Health reported last month it had one diagnosis this season, but on Thursday it said there were two more: in Atlanta and Union counties.

The disease is one of the most dangerous mosquito-borne diseases in the United States, with a fatality rate of 33% in humans, according to the Centers for Disease Control and Prevention. About 90% of the horses that are stricken with the disease die, it said.

Infections are seasonal, mostly from late spring through early fall, but cases rarely occur in winter.

Transmission of the virus is most common in and around swamps in the Atlantic and Gulf Coast states and in the Great Lakes region, the CDC said.

The virus is transmitted to people and animals through a mosquito bite. It cannot be transmitted from one person to another, or from an animal to a person. In the United States, an average of seven human cases are reported annually, the agency said.

Early symptoms usually appear about 4 to 10 days after exposure to the virus. They include headache, high fever, chills and aches. Symptoms can develop into brain swelling, which can result in headache, disorientation, tremors, seizures and paralysis, the Michigan statement said.

There is no human vaccine or specific anti-viral treatment, the CDC said. It said people with symptoms should consult a health care provider for a diagnosis.