An outbreak of a deadly brain infection in the US is raising questions about whether climate change has affected the spread of the mosquito species that carry the disease.
According to the Centers for Disease Control and Prevention, 31 cases of eastern equine encephalitis have been confirmed, including nine deaths, making it the worst outbreak in decades.
The published numbers show that most of the cases have come from Massachusetts, with 12 reported cases and three deaths. Michigan follows closely with nine reported cases and three deaths. The Centers for Disease Control and Prevention (CDC) typically report an average of seven neuroinvasive cases per 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 there is no specific vaccination or treatment. About 30% of people with Eastern Equine Encephalitis (EEE) die, according to the CDC, and those who survive often face 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 to a number of environmental factors.
Transmission of the disease is dependent on mosquitoes that can act as a bridge between infected birds and uninfected humans.
Edward Walker, a professor of entomology at Michigan State University, said he believes the most important bridge vector mosquito species for the EEE virus is the cattail mosquito. Typically, there is a generation of species in your region that peaks in mid-July and disappears in numbers in late August. This year, "we are still catching them now," he said.
"This suggests to me that they are living a long time or that there is a partial second generation," he added.
Skinner said there will likely be fewer EEE cases 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 remove mosquito breeding sites from their homes.
"EEE is one of the most serious diseases transmitted by mosquitoes that we see in terms of the consequences it can have on people's health," he said and closed. "But it is something that can be prevented if people adhere to the precautions that we recommend."