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, North Carolina 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 deaths occurred between mid-August and early September, according to the Michigan Department of Health and Human Services.
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. The state reported six cases in 2002, the last time it recorded a large number of people with the virus.
In Massachusetts, there was one fatality in nine confirmed cases so far this year, state authorities said on Wednesday. One person in West Warwick, R.I., died from the disease, out of three cases in the state, health authorities in that state reported on Tuesday. The Rhode Island Department of Health announced Thursday it was conducting a second round of aerial spraying across the state.
“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, one of the fatal cases was in Kalamazoo County, which is south of Grand Rapids, the statement said. The man who died there 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 E.E.E. for this season.
The commissioner of the Department of Public Health, Renée D. Coleman-Mitchell, said in a statement Monday that an adult in East Lyme had tested positive for the disease after falling ill during the last week of August with encephalitis, and was in the hospital.
“Other states throughout the Northeast are also experiencing an active season for E.E.E.,” 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 Atlantic and Union Counties. Kelly Conner, a press assistant in the communications office at the North Carolina Department of Health, said there had been one case in Catawba County.
The disease is one of the most dangerous mosquito-borne diseases in the United States, with a fatality rate of 33 percent in humans, according to the Centers for Disease Control and Prevention. About 90 percent of the horses that are stricken with the disease die, it said.
Mark Fischer, an epidemiologist in the C.D.C.’s Arboviral Diseases Branch, said this year’s increase in cases had not set off any alarms. “It’s normal to see spikes from year to year,” he said. “However, we are seeing a higher level of activity than in recent years.”
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 C.D.C. 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 four 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 antiviral treatment, the C.D.C. said. It said people with symptoms should consult a health care provider for a diagnosis.
Mr. Fischer also noted that E.E.E. is far less common than West Nile virus, which has had 20 times more cases this year.
“Eastern Equine Encephalitis can be scary; we understand the concern because it’s a serious disease,” Dr. Fischer said. “But it’s a rare disease. People should know that they can take action to protect themselves.”
Jaclyn Peiser contributed reporting.
An earlier version of this article misstated the name of a county where the New Jersey Department of Health reported an E.E.E. diagnosis on Thursday. It is Atlantic County, not Atlanta County.
Christine Hauser is a reporter, covering national and foreign news. Her previous jobs in the newsroom include stints in Business covering financial markets and on the Metro Desk in the police bureau. @ChristineNYT