[Imported Infectious Diseases of the Nervous System]

Although sanitary conditions in Japan are generally favorable, pathogens may be introduced by patients who acquire the infections overseas. Dengue fever has a high global incidence, with nearly 200 cases occurring annually in Japan. Most of these infections are acquired in Southeast Asia. As dengue fever is transmitted by mosquitoes, preventive measures against insect bites are important. The incidence of Japanese encephalitis has markedly decreased in Japan owing to widespread vaccination. This disease is mosquito-borne, and only approximately 1% of infected individuals develop symptoms. However, once symptoms appear, the mortality rate is 20-30%. A characteristic clinical feature of this condition is the presence of extrapyramidal symptoms. Rabies is a representative disease transmitted through dog bites. In Japan, its incidence has dramatically declined owing to canine vaccination and the control of stray dogs. Once rabies develops, the fulminant form accounts for 70-80% of cases. Measles is a representative disease that is transmitted between humans. It is highly contagious and requires careful monitoring. During the coronavirus disease-19 pandemic, the number of measles cases decreased. Recently, the trend has reversed, with many patients believed to have been infected in Vietnam.