Eastern Equine Encephalitis

Eastern Equine Encephalitis - Montgomery Alabama

Eastern Equine Encephalitis Virus, or EEEV for short, is a disease spread by mosquitoes.

It’s fairly rare in humans, with only a few people coming down with it every year. Most have very few symptoms, although EEEV can lead to brain inflammation and serious health problems.

History and Origin

EEEV is a virus that is found in mostly swampy areas where few people live.

That’s why there aren’t that many reported cases of EEEV. It’s carried by birds and by a strain of mosquito that doesn’t bite humans, although it can be passed to mosquitoes that do bite both horses and humans. ¹

This virus was first discovered in 1831 in Massachusetts following the unknown cause of the death of 75 horses. After the bodies were examined, the virus was identified.

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Today, EEEV can be found in the eastern part of the U.S.

The first human cases of EEEV occurred in 1938 when a number of children died from the disease in conjunction with an outbreak among horses in the area. ³

EEEV is similar to the Western equine encephalitis virus and the Venezuelan equine encephalitis virus.

Eastern Equine Encephalitis Incidence Map - CDC
A map of reported human cases of Eastern Equine Encephalitis from 1964-2010.

How it Spreads

This virus is spread by mosquitoes that are infected with it.

The cycle between birds and the mosquitoes that are the primary host to EEEV does not affect humans, but when a bridge species of mosquito is infected, EEEV can be spread to animals and humans.

Once bitten, a human or horse is a dead-end host; i.e., there is not enough of the virus in the blood for another mosquito to become a carrier.

On average, there are eight outbreaks of EEEV in the U.S. every year.

Most of these victims are in Georgia, Florida, New Jersey, and Massachusetts. Those who are younger than 15 or older than 50 are especially susceptible to EEEV.


In humans, the early symptoms of EEEV include:

  • muscle pain
  • a high fever
  • headache
  • anorexia
  • vomiting
  • seizures
  • sensitivity to light
  • meningeal irritation
  • confusion

These symptoms usually come on anywhere from three to ten days following being bitten by a mosquito that carries the virus. As the disease continues, the brain may swell and the patient can fall into a coma and die.

Generally, EEEV accelerates very quickly. Some may fall into a coma in as little as a week.


There is no cure for EEEV, nor is there any specific treatment for the illness.

Supportive treatment is often done, but even so, about a third of all people who are diagnosed with EEEV die from the disease. Those who do recover from EEEV will often have anywhere from fairly mild to very severe neurological damage for the rest of their lives.

Very few people fully recover from EEEV.


There is a vaccine for horses that kills the virus, but there is no vaccine for humans.

The only real way to prevent the disease is to avoid being bitten by mosquitoes. It is believed that having EEEV once does prevent a person from being re-infected, although this is not confirmed.


¹ Learn more about Eastern Equine Encephalitis on the Centers for Disease Control and Prevention website

² Source: Wiktionary

³ Source: Tech Times – “Deadly eastern equine encephalitis virus (EEE) detected in mosquitoes in Massachusetts: How to protect yourself.”

By Centers for Disease Control and Prevention [Public domain], via Wikimedia Commons