Japanese encephalitis is primarily transmitted by the bite of the culex tritaeniorhynchus mosquito. For many years the infection rate of this disease has been dropping due to a comprehensive program of childhood inoculation. The appearance now of the adult form of the disease may be related to an incomplete inoculation program or a diminution of antibodies in the blood of the population.
日本腦炎主要是透過三斑家蚊叮咬傳染，多年來，由於推行幼兒全面接種疫苗，自然感染率下降；如今出現成人感染，可能與預防接種不完全或抗體逐漸減少有關。