Eastern Equine Encephalitis

Eastern equine encephalitis is among the most serious of a group of mosquito-borne viral diseases that can affect the central nervous system. This disease is found mainly along the eastern seaboard of the United States and on the eastern Gulf Coast. Symptoms can start with fever, headache, and other flu-like symptoms; however, these symptoms can sometimes escalate to seizure, coma, brain damage, and death. Since 1964, 163 cases of eastern equine encephalitis have been confirmed in the United States.

 

An Introduction to Eastern Equine Encephalitis

Eastern equine encephalitis is a rare disease that is spread to horses and humans by infected mosquitoes. It is one of several mosquito-borne viral diseases that can affect the central nervous system and cause severe complications, including death.
 
Eastern equine encephalitis is found mainly along the eastern seaboard of the United States and on the eastern Gulf Coast. Currently, there is no specific treatment for eastern equine encephalitis; caregivers focus on relieving the symptoms. Prevention of eastern equine encephalitis centers on controlling mosquitoes and avoiding mosquito bites.
 
Eastern equine encephalitis is among the most serious of a group of mosquito-borne viral diseases. Other similar diseases include:
 

Eastern Equine Encephalitis Virus

Eastern equine encephalitis is caused by the eastern equine encephalitis virus, an arbovirus. Arbovirus is short for arthropod-borne virus. Arboviruses are viruses that are spread by certain invertebrate animals (arthropods), most commonly blood-sucking insects. In the United States, arboviruses are spread mainly by infected mosquitoes. Birds are the source of infection for mosquitoes, which can sometimes transmit the infection to horses, other animals, and, in rare cases, people.
 

Areas Where Eastern Equine Encephalitis Is Commonly Found

Eastern equine encephalitis is found in:
 
  • North America
  • Central and South America
  • The Caribbean.
     
In the United States, most cases of eastern equine encephalitis have been reported from the eastern seaboard states, the Gulf Coast, and some inland midwestern areas.
 

Transmitting Eastern Equine Encephalitis

The eastern equine encephalitis virus has a complex life cycle involving birds and a specific type of mosquito, Culiseta melanura, that lives in marshes and swamps. These mosquitoes feed only on birds; they do not feed on humans and other mammals. In rare cases, however, the eastern equine encephalitis virus can escape from its marsh habitat in other mosquitoes that feed on both birds and mammals (including horses and humans). These mosquitoes can transmit the eastern equine encephalitis virus to animals and people. After infection, the eastern equine encephalitis virus invades the central nervous system, including the spinal cord and brain.
 

Symptoms of Eastern Equine Encephalitis

Eastern equine encephalitis infection can cause a range of illnesses. Most people have no symptoms; others get only a mild flu-like illness with:
 
For people with an eastern equine encephalitis infection of the central nervous system, a sudden fever and severe headache can be followed quickly by seizures and coma. About half of these patients die from the disease. Of those who survive an eastern equine encephalitis infection, many suffer permanent brain damage and require lifetime institutional care.
 
Eastern equine encephalitis symptoms usually appear 4 to 10 days after the bite of an infected mosquito.
 

Eastern Equine Encephalitis: Diagnosis

Doctors use blood or spinal fluid tests to diagnose eastern equine encephalitis.
 

Who Might Be at Risk for Eastern Equine Encephalitis?

Anyone can get eastern equine encephalitis, but some people are at increased risk:
 
  • People living in or visiting areas where the disease is common
  • People who work outside or participate in outdoor recreational activities in areas where the disease is common.
     
Eastern equine encephalitis occurs mainly in young children and in people over age 55.
 

Possible Complications of Eastern Equine Encephalitis

Eastern equine encephalitis is fatal to about half of those who develop severe symptoms. Of those who survive, many suffer permanent brain damage.
 

How to Treat Eastern Equine Encephalitis

There is no specific treatment for eastern equine encephalitis. No effective antiviral drugs have been discovered, and antibiotics are not effective against viruses. Caring for patients with eastern equine encephalitis usually involves treating the symptoms and complications.
 

Eastern Equine Encephalitis: Statistics

Eastern equine encephalitis is a rare disease. Since 1964, 163 eastern equine encephalitis cases have been confirmed in the United States. Fewer than five eastern equine encephalitis cases are reported in most years.
 
Although small outbreaks of human disease have occurred in the United States, eastern equine encephalitis epidemics in horses can be common during the summer and fall.
 
The risk of exposure to eastern equine encephalitis has been increasing as people move into previously undeveloped areas where the virus lives. Deaths in horses are a sign of increased spread of the virus in a community.
 

Preventing Eastern Equine Encephalitis

An eastern equine encephalitis vaccine is available for horses, but not for humans.
 
Prevention depends on public health action to control mosquitoes and on individual action to avoid mosquito bites. To avoid being bitten by the mosquitoes that carry the eastern equine encephalitis virus:
 
  • If possible, stay inside between dusk and dark (when mosquitoes are most active)
  • When outside between dusk and dark, wear long pants and long-sleeved shirts
  • Use insect repellent on exposed skin.
     
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD