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Japanese encephalitis

Synonym: Japanese B encephalitis
Japanese: nihon nooen
Abbreviation: JE
German: Japanische Enzephalitis

1 Definition

Japanese encephalitis is a tropical disease that is caused by viruses. It is mostly occuring in east and southeast Asia.

ICD10-Code: A83.0

2 Pathogen

The japanese encephalitis is caused by an infection with the Japanese encephalitis virus. This virus belongs, just like the yellow fever pathogen, to the group of flaviviridae. Multiple subtypes of the virus exist including the already identified nakayama and JaGar-01 strains.

3 Infection

The Japanese encephalitis is, in the proper sense, a zoonotic disease. The main pathogen reservoir are wildlife birds (including herons), but also reptiles and bats. Intermediate hosts for the infection of humans are often domesticated animals (pigs, horses). Mosquitos of the culex and aedes genus are vectors that can pass on the virus through their bites. The most important transmitters are culex tritaeniorhynchus, culex fuscocephala and culex annulus.

4 Risk of infection

The risk of infection for tourists is comparatively low. An increased risk of infection is given in endemic regions, and especially in rural areas during the rainy season. Only a fraction of mosquitos are carriers of the virus. The prevalence rate of carriers varies regionally and. The risk of infection increases also proportionally to the amount of mosquito bites.

5 Epidemiology

The Japanese encephalitis is widely prevalent in Asia. In Japan itself the incidence is very low because of systematic vaccination of pets. The highest rates of incidence are in China, Sri Lanka, Myanmar (Burma), Nepal, Vietnam, the Philippines and northern Thailand. Yearly about 35’000 – 50’000 cases, exceeding 10’000 deaths are reported. However, the real number of cases is believed to be significantly higher.

After an infection the patient is left with life-long immunity.

6 Symptoms

In most case the infection takes a mild or even asymptomatic course. In case of a more severe course, flu-like symptoms occur after an incubation period of 5-15 days. The flu-like symptoms include fever, chills, fatigue, headaches, nausea and vomiting.

The virus can also affect the CNS, causing encephalitis with reduction of consciousness, cramping seizures, impaired reflexes, paresis and signs of meningitis. In about 20% these cases lead to the death of the patient. About half of these patients are left with long term neurologic deficits.

7 Diagnostics

A tentative diagnosis can be made from the clinic symptoms following an exposition to the pathogen. Further testing includes:

8 Differential Diagnoses

9 Prophylaxis

Basic measure of prophylaxis is the prevention of mosquito bites. Tourists should make use of repellents, mosquito nets and long-sleeved clothing. In case of a prolonged stay in an endemic region a vaccination against JE is advised. In Germany a dead vaccine is available under the name Ixiaro®. This vaccine is made up of inactivated JE viruses of the genotype III. Alternative vaccines for children, which have not been approved in Germany, are available through international pharmacies. Data for the provided length of immunization are not available yet.

10 Therapy

As of 2015 there was no effective virostatic agent available for the treatment of JE. This means the treatment is limited to reduction of the symptoms and prevention of long term damages. It is focused on the maintenance of the fluid balance, prevention of secondary infections and artificial respiration if needed.


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