Symptoms, Diagnosis, & Treatment


For eastern equine encephalitis (EEE), the time from infected mosquito bite to onset of illness (incubation period) ranges from 4 to 10 days. EEE can result in febrile illness (fever) or neurologic disease, including meningitis (infection of the membranes that surround the brain and spinal cord) or encephalitis (infection of the brain). The type of illness will depend on the age of the person and other factors. Some people who become infected with EEE virus may be asymptomatic (will not develop any symptoms).

Febrile illness is characterized by fever, chills, body aches, and joint pain. The illness lasts 1 to 2 weeks, and most people recover completely when there is no central nervous system involvement.

Signs and symptoms of neurologic disease include fever, headache, vomiting, diarrhea, seizures, behavioral changes, drowsiness, and coma. In infants, neurologic disease often occurs soon after onset; in older children and adults, encephalitis may occur after several days of systemic illness.

  • Approximately a third of all people with encephalitis due to EEE die. Death usually occurs 2 to 10 days after onset of symptoms but can occur much later.
  • Many people who recover are left with long-term physical or mental impairments, which can range from mild brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction.
  • People with severe impairments often require long-term care and die within a few years.

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  • See your healthcare provider if you develop the symptoms described above.
  • Your healthcare provider can order tests to look for EEE virus infection.
  • To learn more about testing, visit our Healthcare Providers page.

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  • No vaccine or specific antiviral treatments for EEE are available.
  • Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms
  • In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
  • If you think you or a family member might have EEE, talk with your health care provider.
  • To learn more about treatment, visit our Healthcare Providers page.

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