Japanese Encephalitis

Japanese encephalitis is a viral infection that was first observed in Japan in 1870. Japanese encephalitis is a vector-borne disease caused by an arbovirus transmitted by a mosquito. With approximately 50,000 cases and 10,000 deaths reported each year, Japanese encephalitis is the most frequent and most severe viral encephalitis, and the leading cause of viral neurological infection among children in Asia. (11)


Symptoms of Japanese encephalitis

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 five 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.


Epidemiology and vaccination against Japanese encephalitis

Japanese encephalitis is mostly seen in rural areas (where humans are in the close vicinity of swine and birds- the main reservoir of the virus), and more particularly in rice fields, an environment favorable to the development of mosquitoes.

Infection usually occurs between April and December, with peaks during the monsoon season.

Prevention is possible through the use of inactivated vaccines.



11 - Japanese encephalitis vaccines. WHO position paper; WER 2006, 81:326-340:


12 - Scott B Halstead, Theodore F. Tsai. Japanese encephalitis vaccines. Plotkin A., Orenstein W. Fourth edition 2004. Saunders Editor p 919-958