1. What is Japanese Encephalitis (JE)?

Japanese Encephalitis (JE) is an infectious disease caused by the Japanese encephalitis virus from the Flaviviridae family. The virus circulates mainly in the environment between mosquitoes and animals (especially wading birds and pigs), and humans get infected after being bitten by an infected mosquito (most often Culex mosquitoes).

Source/reservoir of pathogen: primarily wading birds and pigs; humans are usually "accidental" hosts.
Incubation period: usually approx. 5–15 days (practically a range of several to over a dozen days is given).
Who is most at risk: people staying in rural areas, wetlands, near rice fields and pig farms, especially when spending a lot of time outdoors (e.g., trekking, work, volunteering).

2. Symptoms of Japanese Encephalitis

In most infected people, the infection is asymptomatic. If symptoms appear, initially they may resemble "flu":

fever,
headache,
nausea/vomiting, gastrointestinal ailments,
general malaise.

In a small proportion of patients, the central nervous system is involved, and encephalitis develops with symptoms such as:

high fever,
stiff neck/meningeal symptoms,
disturbances of consciousness, disorientation,
convulsions,
paresis.

Possible complications: permanent neurological and mental sequelae (e.g., movement disorders, muscle weakness, cognitive/behavioral problems). In the severe form of the disease, mortality can reach about 20–30%, and a significant proportion of survivors are left with complications.

Urgent medical consultation is necessary when, after a stay in a risk country, the following appear: high fever + severe headache, stiff neck, disturbances of consciousness, convulsions, neurological symptoms (e.g., paresis).

3. Where does Japanese Encephalitis occur?

The risk mainly concerns Asia and selected areas of the Western Pacific.

For travelers, the most important thing is that the risk increases when:

you go outside large cities, to the countryside, near water bodies/rice fields,
you plan a longer stay or intense outdoor activities (e.g., trekking, biking, camping),
you go during periods of increased mosquito activity (often the rainy season or warm months – depending on the country).

4. How to protect yourself against Japanese Encephalitis?

A. General prevention

Since the infection is transmitted by mosquitoes, protection against bites is key:

repellents on skin and clothing,
long sleeves and trousers (especially in the evening and at night),
mosquito nets (preferably impregnated) and air conditioning/screens in windows,
avoiding staying outdoors during hours of highest mosquito activity (often from dusk to dawn),
caution near wetlands and rice fields (mosquito breeding grounds).

B. Vaccination

The most important method of specific prevention is vaccination. In Europe, the IXIARO vaccine is available – inactivated (killed virus, does not cause disease).

For whom recommended (most often):

people traveling to risk areas, especially for longer stays, trips outside cities, outdoor activities,
people with occupational exposure (e.g., field work, laboratories).

Vaccination schedule (IXIARO):

standard 2 doses in a 0 and 28 days schedule,
in adults 18–65 years, an accelerated schedule is possible: second dose 7–28 days after the first,
last dose at least 1 week before travel.

Booster doses:

a booster dose is considered if ≥1 year has passed since primary vaccination and exposure risk continues,
long-term data indicate the sense of another booster dose after approx. 10 years in people still exposed (before the next exposure).

Duration of immunity: depends on the schedule and further doses; with continuing risk, booster doses according to recommendations are key.

5. Summary

Japanese Encephalitis is a rare disease in tourists, but potentially very severe neurological disease transmitted by mosquitoes. Since there is no causal treatment, prevention is most important: protection against bites and – in people with real risk – vaccination. Vaccination is particularly worth considering for longer trips to Asia, outside cities, with outdoor activities. It is best to start it at least 4–5 weeks before departure (or earlier if you plan more vaccinations), so as to make it in time with 2 doses and keep a minimum of 7 days from the last dose to travel.