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Japanese encephalitis

Japanese encephalitis (JE) is a neurologic infection closely related to West Nile virus and Yellow Fever. An arbovirus (arthropod-borne), the disease is spread by mosquitoes and infects not only humans, but also most domestic animals, birds, bats, snakes and frogs. Because domestic pigs act as an amplifying host, and the Culex tritaeniorhynchus mosquito breeds in flooded rice fields, the disease is endemic in rural areas.

Most infected persons develop mild symptoms or no symptoms at all. However, in the 50,000 people who subsequently develop encephalitis, approximately 30% will die, and the 40% who are brain damaged as a result of the infection make JE the leading viral cause of disability in Asia. Currently, approximately 3 billion people live in areas endemic for Japanese encephalitis; these areas extend from Pakistan to maritime Siberia and Japan.

An effective vaccine has existed since 1941, but its routine use has not been possible for the poorest countries in Asia. This inactivated mouse brain derived vaccine has, however, successfully reduced the incidence of JE in Japan, Taiwan, Korea, Thailand, and Vietnam. The vaccine's slow uptake can be attributed to a multitude of factors: it is very expensive (15 to 20$ for 3 doses), there are no universal guidelines for its use, and, compared to other vaccines, there is a high likelihood of contaminants in the vaccine causing adverse reactions. Control of this disease has been further limited due to poor disease surveillance, a limited and unstable vaccine supply, and lack of public visibility.

There are currently several promising candidate vaccines that could be developed for a broader market. One, produced in China, has been administered to at least 200 million Chinese children over the last 12 years. It has an estimated cost of less than a dollar a dose, and requires a single dose to be effective, but further work is needed.

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