Editor's note: This story was updated Oct. 15, Oct. 2 and Sept. 26, 2019 with changes to the number of deaths.
Sept. 25, 2019 -- This is a particularly bad season for the potentially fatal Eastern equine encephalitis -- the rare mosquito-borne EEE that has infected almost 30 people from seven states this year. Twelve of them have died. In the United States, an average of seven EEE cases are reported each year, according to the CDC.
Even though the number of confirmed cases is still very low compared to, for instance, West Nile virus, many governments are urging people to stay indoors or are increasing their mosquito spraying programs. One reason for the concern is that an estimated 30% of people who get EEE die from it.
WebMD talked to William Schaffner, MD, an infectious diseases specialist at Vanderbilt University Medical Center, about the infection, its effect on the body, and how to avoid it:
WebMD: What makes EEE so dangerous?
Schaffner: This is a virus that does not normally infect humans. When it gets into people, it is a very nasty infection. It has an attraction to the central nervous system, especially the brain. When it gets to the brain, it destroys brain cells. It creates an inflammatory response, which causes fluid to get around the brain. The brain is encased by the skull, so it can't expand, causing increased pressure, which compromises brain function.
WebMD: Why are there more cases this year?
Schaffner: We're not entirely sure. Let's put it into context: This is a pretty unusual infection in humans. The virus circulates among wild birds and is transmitted by mosquitoes. It lives in that ecologic niche, particularly swampy water. That's its habitat. It's been an infection largely on the Gulf Coast and East Coast. Occasionally, a different mosquito species gets in the middle of this -- one species that will bite both horses and humans, so infections can occur in those species.
It has raised speculation about climate change. One of the things that will happen, if you get a wetter and warmer climate and more prolonged seasonal warmth, you get more mosquitoes. That's an increased opportunity to exploit this ecologic niche. The military calls it collateral damage -- you get infection in horses, and in people -- species that are not usually part of the virus ecology.
WebMD: Why does it generate more fear than, say, West Nile, which is more common?
Schaffner: Unusual things that crop up get more attention. Of people who survive, they almost invariably have some permanent disability. It destroys brain tissue and does so very aggressively.
WebMD: How do people usually come to realize they have EEE?
Schaffner: They get sick very quickly. It has to be within the differential diagnosis of doctors taking care of them. The onset is usually quite abrupt. You have high fever, vomiting, and you suddenly get very sleepy. That can turn into stupor and coma. The brain doesn't work as well -- you can have convulsions. You can quickly have difficulty breathing. Diagnosis relies on serologic tests, which look for antibodies in the blood.
WebMD: What can doctors do for patients with EEE?
Schaffner: The important thing is to stabilize the patient while the body fights the infection. There’s no specific antiviral medication.
WebMD: What can people do to avoid it?
Schaffner: You need to do everything you can to avoid mosquito bites. People need to be using a lot of insect repellent when they go out, particularly in the morning and evening. Long sleeves and long trousers help avoid mosquito bites. It's helpful to police the area -- go around your home and look for any standing water, even birdbaths. Standing water, even small amounts, can be mosquito breeding sites.
Our preventive measures are simple, but you have to remember to do them all the time. Because one mosquito bite can get you.