JAPANESE ENCEPHALITIS

Japanese encephalitis (JE), a mosquito-borne arboviral infection, is the leading cause of viral encephalitis in Asia. JE virus is related antigenically to the flaviviruses of St. Louis encephalitis and Murray Valley encephalitis, and to West Nile virus.

Infection leads to overt encephalitis in only 1 of 20 to 1,000 cases. Encephalitis usually is severe, resulting in a fatal outcome in 25% of cases and residual neuropsychiatric sequelae in 30% of cases.

The risk for developing JE after a mosquito bite can be factored into a series of probabilities. Only bites of vector mosquitoes pose a risk and fewer than 3% of vector mosquitoes are likely to be infected. Only one of approximately 200 infections leads to neuroinvasive disease. The use of bed nets, insect repellents and protective clothing, and avoidance of outdoor activity, especially during twilight periods and in the evening, will reduce risk even further.

SYMPTOMS

• Encephalitis is the major form of the disease, although other, less severe forms, such as aseptic meningitis or simple febrile syndromes accompanied by headache, are also frequent.

• After an incubation period of 5 to 15 days, the disease is characterized by the abrupt onset of high fever accompanied by headaches, behavioral changes, as well as speech and motor disorders (paralyses).

• The evolution of the disease is marked by the gradual onset of consciousness disorders that can evolve to coma. The mortality rate of Japanese encephalitis is high and sequelae are common, especially among children (up to 50%). (12)

• There is no specific treatment for the disease.