Symptoms & Treatment
The incubation period for Eastern equine encephalitis virus (EEEV) disease (the time from infected mosquito bite to onset of illness) ranges from 4 to 10 days. EEEV infection can result in a systemic febrile illness 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 host factors. Some people who become infected with EEEV may be asymptomatic (will not develop any symptoms).
Systemic infection is characterized by fever, chills, malaise, arthralgia, and myalgia. The illness lasts 1 to 2 weeks, and most people recovery 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 EEEV infection die. Death usually occurs 2 to 10 days after onset of symptoms but can occur much later. Of those who recover, many are left with physical or mental sequelae, which can range from mild brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction. Many patients with severe sequelae require long-term care and die within a few years.
There is no approved human vaccine or specific antiviral treatment for EEEV infections. Patients with suspected EEEV disease should be evaluated by a healthcare provider, appropriate serologic and other diagnostic tests ordered, and supportive treatment provided.
Cerebrospinal fluid (CSF) findings include neutrophil-predominant pleocytosis and elevated protein levels; glucose levels are normal. Neuroimaging shows brain lesions consistent with encephalitis, including neuronal destruction and vasculitis in the cortex, midbrain, and brain stem. There is minimal involvement of the spinal cord.
EEEV is difficult to isolate from clinical samples; almost all isolates (and PCR positive samples) have come from brain tissue or CSF. Serologic testing remains the primary method for diagnosing EEEV infection. Combined with a consistent clinical presentation in an endemic area, a rapid and accurate diagnosis of acute EEEV disease can be made by the detection of EEEV-specific IgM antibody in serum or CSF. EEEV IgM testing is available at CDC and some state health departments. A positive EEEV IgM test result should be confirmed by neutralizing antibody testing at a state public health laboratory or CDC. To submit specimens for testing at CDC, please contact your state health department.
All EEEV disease cases should be reported to local public health authorities. Reporting can assist local, state and national authorities to recognize outbreaks of this rare disease and to institute control measures to limit future infections.