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Eastern Equine Encephalitis Virus

Eastern equine encephalitis virus (EEEV) is an arthropod-borne virus (arbovirus) that is primarily transmitted in Indiana by mosquitoes in the genus Coquillettidia. People infected with EEEV can develop severe inflammation in the brain. Only a few cases of EEEV disease are reported in the United States each year. Most occur in eastern or Gulf Coast states.

On this page:

Transmission | Signs and Symptoms | Diagnosis | Treatment | Prevention | Maps and Statistics | Resources | Information for Providers

Eastern equine encephalitis virus. Centers for Disease Control and Prevention.


EEEV can be transmitted in Indiana by mosquitoes in the genus Coquillettidia, but some members of the genus Aedes may also play a role in transmission to humans and animals. These mosquitoes become infected when they feed on infected wild birds. Infected mosquitoes can then spread EEEV to people, horses, and other mammals. Once infected, people and other mammals are “dead-end hosts,” which means that they do not pass the virus on to other biting mosquitoes.  

Signs and Symptoms

Signs and symptoms of EEEV disease usually appear within 4 – 10 days of a bite from an infected mosquito. EEEV infection can result in one of two types of illness, systemic or encephalitic (involving swelling of the brain). It is possible that some people who become infected with EEEV may not develop any symptoms.

Symptoms of systemic EEEV infection appear abruptly and include chills, fever, body aches, and joint pain. People with systemic EEEV infection are usually sick for 1 to 2 weeks and recover completely if the infection does not spread to the central nervous system. In some older children and adults, systemic EEEV infection can progress to encephalitis (inflammation of the brain). In infants, encephalitis can happen abruptly.

Approximately one third of all cases of encephalitis due to EEEV are fatal. Many people who recover will experience severe ongoing complications. People who are younger than 15 years and older than 50 years are at the greatest risk of severe disease if infected with EEE virus. 


Diagnosis of EEEV disease is based on the patient’s signs and symptoms and appropriate laboratory testing. If you think you have EEEV disease, contact your healthcare provider.


No specific medication is available to treat EEEV disease. People with severe illness usually require hospitalization, supportive care, and/or rehabilitation.


The best way to prevent EEEV disease is to avoid mosquito bites. See our mosquito prevention page for more information. 

For more information about Eastern Equine encephalitis virus, visit the CDC EEEV webpage.

Maps and Statistics

While equine cases are occasionally detected, human EEEV disease is rare in Indiana. No cases were reported from 2013–2017. For more information, please visit:

For maps showing recent EEEV infections in people, horses, and mosquitoes, click here.

National statistics for EEEV disease can be found at the CDC EEEV Statistics and Maps webpage.


EEEV Quick Facts

Information for Providers

For EEEV disease diagnosis, treatment, and testing information, click here.


Page Last Updated: February 20, 2020

Page Last Reviewed: July 22, 2019