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| JAPANESE ENCEPHALITIS |
Disease
Japanese B Encephalitis is an arbovirus which is transmitted in humans through mosquito bite. The incubation period is between 5-15 days. Though disease occurs in all ages but children are highly affected in endemic areas. The acute encephalitis usually lasts from few days to as long as 2-3 weeks but the recovery is very slow, with weeks or months required for the return of maximal recoupable function.
Occurrence
Japanese Encephalitis virus is found throughout Asia including far eastern Russia, Japan, China, India, Pakistan, and South East Asia and causes occasional epidemic on western pacific islands. The disease is found in areas where abundant breeding of mosquitoes takes place, which transmit the disease to humans.
Risk for travellers
Japanese encephalitis (JE) is the leading cause of viral encephalitis in Asia and occurs in almost all Asian countries. Its incidence has been declining in Japan and the Korean peninsula and in some regions of China, but is increasing in Bangladesh, India, Nepal, Pakistan, northern Thailand and Viet Nam. Transmission occurs principally in rural agricultural locations where flooding irrigation is practiced–some of which may be near or within urban centres. Transmission is seasonal and mainly related to the rainy season in south-east Asia. In the temperate regions of China, Japan, the Korean peninsula and eastern parts of the Russian Federation, transmission occurs mainly during the summer and autumn. Vaccination is not recommended for all travellers to Asia because of the low incidence of the disease in travellers and potential (although rare) adverse events: it should be based on individual risk assessment, taking into account the season, the type of accommodation and the duration of exposure, as well as the travel itinerary.
The risk to short-term travellers and those who travel mainly to urban areas is very low. Vaccination is recommended for travellers with extensive outdoor exposure (camping, hiking, bicycle tours, outdoor occupational activities, in particular in areas where flooding irrigation is practiced) in rural areas of an endemic region during the transmission season. It is also recommended for expatriates living in endemic areas through a transmission season or longer.
Vaccine
This vaccine is recommended either for those living in endemic areas or during epidemics for travellers as aforementioned.
Three types of JE vaccine are currently in large-scale production and use: inactivated mouse-brain-derived vaccine (IMB), cell-culture-derived inactivated vaccine and cell culture-derived live attenuated SA 14-14-2 vaccine. At present, the IMB vaccine is the most widely available commercially, but its production will cease in the near future. New vaccines are in the final stage of development.
For children aged 1–3 years, the mouse-brain-derived vaccine provides adequate protection throughout childhood following two primary doses 4 weeks apart and boosters after 1 year and subsequently at 3-yearly intervals until the age of 10–15 years.
Live attenuated SA14-14-2 vaccine gives equally good protection with a single dose followed, as required, by a single booster dose given at an interval of about 1 year
Vaccine for travellers: Two doses inactivated vaccine or one dose of live attenuated vaccine is given before departure. |
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