At least 11 people have died from a rare mosquito-borne illness in the United States

A fourth person in Michigan has died of the rare Eastern Equine Encephalitis mosquito virus, raising the death toll to eleven nationwide.

Calhoun County officials received confirmation Wednesday that a Battle Creek resident died from EEE complications. With such a high concentration in Michigan, officials scheduled aerial pesticide treatments for Wednesday night for parts of the state. Residents were able to opt out of the pesticide spray.

This year has seen an unusual uptick in the number of reported cases and deaths. Typically, there are only five to 10 human cases reported in the US each year, with about 30% of all cases resulting in death, according to the US Centers for Disease Control and Prevention.

EEE is a rare virus spread through mosquitos. The illness can cause brain swelling preceded by flu-like symptoms, including a high fever, chills and nausea. Severe cases can result in seizures or a coma that can cause brain damage, the CDC said.

In addition to the Michigan deaths, three people have died in Massachusetts, three in Connecticut and one person has died in Rhode Island.

“Before this year, we have had only one human case of EEE in Connecticut, and that was in 2013,” Dr. Matthew Cartter with the Connecticut Health Department said.

A vaccine for EEE is on the market for horses, but not for humans.

There have been six confirmed cases among horses in Connecticut this year. Lt. Gov. Susan Bysiewicz has attributed the spread of the virus to climate change, citing the number of infections in nearby states and the number of cases that have happened so late in the year.

“We continue to emphasize the need for people to protect themselves from mosquito bites,” Massachusetts Public Health Commissioner Monica Bharel said in a news release last month. “It is absolutely essential that people take steps to avoid being bitten by a mosquito.”

The CDC recommends residents of impacted areas use insect repellant and avoid the outdoors after dark to lessen their risk.