An outbreak of a deadly brain infection is raising questions about whether climate change has affected the spread of the mosquito species that carry the disease.

There have been 31 confirmed cases of Eastern equine encephalitis, including nine deaths, according to the Centers for Disease Control and Prevention, making it the worst outbreak in decades.

Numbers released yesterday show the majority of cases have come out of Massachusetts, with 12 reported cases and three deaths. Michigan follows close behind with nine reported cases and three deaths. The CDC normally reports an average of seven neuroinvasive cases a year.

While the cause of the large outbreak is uncertain, the disease, also known as EEE, is one of many mosquito-borne diseases that researchers say could spread as a result of climate change (Climatewire, March 7).

EEE is a rare cause of brain infections, and no vaccination or specific treatment exists. About 30% of people with EEE die, according to the CDC, and those who survive often deal with ongoing neurological problems.

CDC spokesman Thomas Skinner said the high number of cases this year is unusual. He attributed it to the distribution of mosquitoes that caused the disease and a number of environmental factors.

Transmission of the disease depends on mosquitoes that can act as a bridge between infected birds and non-infected humans.

Edward Walker, a professor of entomology at Michigan State University, said he believes the important bridge vector mosquito species for the EEE virus is the cattail mosquito. Normally, there is one generation of the species in his region that peaks in mid-July and trails off in numbers by late August. This year, “we are still catching them now,” he said Monday.

“This suggests to me that they are either living a very long time or there is a partial second generation,” he said.

Skinner said there will likely be fewer cases of EEE once states see a hard freeze. But given there are several weeks left in mosquito season, he says he hopes people will continue to protect themselves from bites and eliminate mosquito breeding sites from their homes.

“EEE is one of the more serious mosquito-borne diseases that we see as far as the consequences it can have on people’s health,” he said. “But it’s one that can be prevented if people adhere to the precautions we recommend.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news