Japanese encephalitis (JE) is a mosquito borne viral disease prevalent in rural areas of Asia & Indonesia. In temperate zones of China, Japan, Korea & eastern Russia the carriers are present in greatest numbers from June through September & are inactive during winter months. Elsewhere, seasonal patterns of disease are more extended or vary with the rainy season & irrigation practices so although a general seasonal trend for a particular geographic area can be given the risks in sub-tropical & tropical zones are unpredictable.
HOW THE DISEASE IS TRANSMITTED
JE virus is transmitted by the bites of the Culex genus of mosquitoes which tend to feed outdoors at dusk & during evening hours until dawn. Larvae are found in flooded rice fields, marshes, & small stable collections of water around cultivated fields. Swine & certain species of wild birds actually amplify the virus in their bloodstreams when bitten so areas where these creatures are prevalent are areas of high risk. Habitats supporting the transmission cycle of JE virus are principally in rural, agricultural locations
Most infections produce no symptoms at all & result in natural immunity. However, in a few patients the viruses enter the nervous system causing encephalitis (brain fever) characterised by fever & confused consciousness (delirium or stupor) & among these patients there is a 30% risk of dying; in those who survive about half will be left with some form of brain damage or paralysis. Children are at greatest risk but multiple factors such as occupational or recreational exposure, previous vaccination or naturally acquired immunity, & of course mosquito prevalence, affect the potential for infection & illness.
PREVENTION & CURE
The risk to short-term (less than 30 days) travelers & persons who confine their travel to urban centers is very low. Expatriates & travelers living for prolonged periods in rural areas are at greatest risk but travelers with unprotected outdoor evening & night time exposure in rural areas, such as bicycling, camping or certain occupational activities, may be at high risk even if their trip is brief. Travelers are advised to stay in screened or airconditioned rooms, to use bednets when such quarters are unavailable, to use insecticidal space sprays as necessary, & mosquito repellents & protective clothing to avoid mosquito bites.
Traditionally a 3 dose inactivated vaccine made in mouse-brain, manufactured in Japan, has been used. This is being phased out as new safer, more efficient vaccines become available.
While many Asian countires now use a Chinese made live vaccine, this is not licenced in Australia.
The two vacines that will be soon licenced in Australia are:
An inactivated 2-dose vaccine made in vero cells, & a single dose live-attenuated vaccine, based on the yellow fever vaccine, & inducing longterm immunity.
Both of these will be safer & more effective than the "old" vaccine.