Japanese encephalitis (JE) (thesaurus synonyms: encephalitis japonica B; Japan B encephalitis; Japanese encephalitis; Russian autumn encephalitis; ICD-10-GM A83.0: Japanese encephalitis) is an infectious (tropical) disease caused by Japanese encephalitis virus (JEV).
JEV is an arbovirus (arthropod-borne virus) that, like the causative agent of dengue fever and yellow fever, belongs to the Flaviviridae. So far, 5 genotypes of the virus have been identified.
The disease belongs to the viral zoonoses (animal diseases).
Pathogen reservoirs are mainly wild birds (especially waterfowl such as herons) and pigs kept as domestic animals.
Occurrence: The pathogen is found predominantly in eastern Russia, Japan, China, India, Pakistan, and Southeast Asia (Indonesia, Philippines, Vietnam, and northern Thailand). In the past, the virus was most prevalent in rural areas, but recently cases have been reported in urban areas.
Seasonal incidence of the disease: Japanese encephalitis occurs more frequently between spring and autumn. In tropical areas during the rainy season.
Transmission of the causative agent (route of infection) is by the nocturnal Culex mosquitoes (especially C. tritaeniorhynchus (rice field mosquito)).
The incubation period (time from infection to onset of disease) is usually 4-14 days. However, only about 1 in 250 infected persons experience symptoms after the incubation period.
Peak incidence: the disease occurs predominantly in children.
Japanese encephalitis is the most common viral encephalitis in Asia. In endemic areas, 30,000-50,000 cases are reported annually.
The disease leaves lifelong immunity.
Course and prognosis: In young adults and otherwise healthy individuals, the disease is usually mild to asymptomatic (without symptoms). Severe courses occur in children and the elderly. The recovery process takes several weeks. In 35-50% of those affected, the disease leaves permanent neurological and/or psychiatric damage.
The lethality (mortality in relation to the total number of people affected by the disease) is about 20-30% in cases of CNS involvement.
Vaccination: vaccination against Japanese encephalitis is available and recommended for travelers.