Eastern equine encephalitis (EEE) is a rare disease that is spread to horses and humans by infected mosquitoes. It is among the most serious of a group of mosquito-borne virus diseases that can affect the central nervous system and cause severe complications and even death.

Similar diseases are western equine encephalitis, St. Louis encephalitis, and LaCrosse encephalitis.

The virus can be found in the eastern, Gulf, and north-central areas of the U.S. Most activity occurs between May and August but it can be seen throughout the year in Florida. 

TRANSMISSION: These mosquitoes can transmit the virus to animals and people. After infection, the virus invades the central nervous system, including the spinal cord and brain. In addition to horses, other animals such emus and ostriches and camelids (alpacas and llamas) can also be impacted by EEE.

• Eastern equine encephalitis is caused by a virus usually spread to people through the bite of an infected mosquito.
• Eastern equine encephalitis virus circulates in the environment between mosquitoes and birds typically found in swamps.
• The virus can rarely be transmitted through solid organ transplantation.

SYMPTOMS: Most people infected with eastern equine encephalitis virus do not develop symptoms. For those who develop symptoms, the time from an infected mosquito bite to onset of illness (incubation period) ranges from 4 to 10 days. Eastern equine encephalitis virus infection can result in febrile illness (fever) or neurologic disease. The type of illness will depend on the age of the person and other factors.

TREATMENT: There is currently no therapeutic treatment for EEE. Current methods consist primarily of symptom treatment and supportive care.

• A vaccine has been developed and is in use for horses, as the case-fatality in equines is 80-90%
• There is currently no vaccine for humans.

FOR MORE INFO, visit Eastern Equine Encephalitis - Florida Department of Health.