Eastern equine encephalitis (EEE) is a rare but serious viral disease spread by mosquitoes that can affect people and horses. EEE can also cause disease in captive birds such as the ring-necked pheasant, emu, ostriches, quail and ducks. EEE infection and disease can occasionally occur in other livestock, deer, dogs, other mammals, reptiles and amphibians. Symptoms: Most people bitten by an infected mosquito will not develop any symptoms. Severe cases of EEE infection begin with the sudden onset of headache, high fever, chills, and vomiting. The illness may then progress into disorientation, seizures, encephalitis (inflammation of the brain) and coma. Approximately a third of patients who develop EEE die, and many of those who survive have mild to severe brain damage. It takes 4-10 days after the bite of an infected mosquito to develop symptoms of EEE. Diagnosis and Treatment: The physical examination for EEE also is nonspecific, yielding findings similar to those seen with many other encephalitides. Changes in vital signs may include the following:
Neurologic findings may include the following:
Focal sensory or motor deficit
Depressed or hyperactive reflexes
Epidemology: The incidence of encephalitis is 1 case per 200,000 population in the United States, with herpes simplex virus (HSV) being the most common cause. The arboviruses account for 10% of cases; occasionally, during an epidemic, they can account for as many as 50%. EEE was first recognized in 1938. From 1955-1997, 256 cases, both sporadic and epidemic types, were reported to the US Centers for Disease Control and Prevention (CDC). Most infections occur in summer or early fall. The vector population usually dies in winter, and cases of EEE are almost nonexistent in winter months; however, after winter, a repetitive endemic locus of infection may persist. An additional risk increase occurs during epizootic outbreaks among horses or caged birds. EEE is a summertime disease and most commonly affects people younger than 15 years and older than 55 years. The exact reason for this pattern is not known, but the preference for extremes of age is a characteristic common to many species of the alphavirus family. Patient age does not affect prognosis, but permanent neurologic impairment and death are more common in children.