Encephalitis generally results from infection with arboviruses specific to rural areas. In urban areas, it’s most frequently caused by enteroviruses (coxsackievirus, poliovirus, and echovirus).

Other causes include herpesvirus, mumps virus, human immunodeficiency virus, adenoviruses, and demyelinating diseases after measles, varicella, rubella, or vaccination.

Between World War I and the Depression, a type of encephalitis known as lethargic encephalitis, von Econ-omo’s disease, or sleeping sickness occurred with some regularity. The causative virus was never clearly identified, and the disease is rare today. Even so, the term sleeping sickness persists and in many cases is mistakenly used to describe other types of encephalitis as well. The most recent outbreak of mosquito-borne encephalitis was West Nile encephalitis.

All viral forms of encephalitis have similar clinical features, although certain differences do occur.

Usually, the acute illness begins with sudden onset of fever, headache, and vomiting and progresses to include signs and symptoms of meningeal irritation
(stiff neck and back) and neuronal damage (drowsiness, coma, paralysis, seizures, ataxia, and organic psychoses). After the acute phase of the illness, coma may persist for days or weeks.