**1. Introduction**

Japanese encephalitis (JE) is among the most significant viral encephalitis in Asia, particularly in rural and suburban areas where rice culture and pig farming coexist. It has also occurred rarely and occasionally in northern Australia and some parts of the western pacific. JE is caused due to infection with the JE virus (JEV), a mosquito borne flavivrus. The main JEV transmission cycle involves *Culex tritaeniorhynchus* mosquitoes and similar species that lay eggs in rice paddies and other open water resources, with pigs and aquatic birds as principal vertebrate amplifying hosts [Han *et al*., 2012]. Humans are generally considered as dead-end JEV hosts i.e. they rarely develop enough viremia to infect feeding mosquitoes. Nearly 20-30% of JE cases are fatal and 30-50% of survivors have major neurological disorders [Bhattacharyya *et al*., 2013]. JE is mostly a disease of children but other age groups may be affected [Kundu *et al*., 2013; Griffiths *et al*., 2013; Larena *et al*., 2013]. In most temperate areas of Asia, JEV is transmitted mainly during summer season, when large epidemics can occur. In the tropics and subtropics region, transmission can occur throughout the year but often increases during the rainy season [Campbell *et al*., 2011]. The first epidemic of JE was recorded in Japan in 1871. Major outbursts have been seen in nearly every 10 years. In 1924 more than 6,000 cases were reported in a major outbreak in Japan [Solomon *et al*., 2000]. The disorders caused by JEV began from Southeast Asia and now it's affecting people worldwide [Liu *et al*., 2013; Li *et al*., 2013]. Nearly 30 million people are at danger of JEV infection [Saxena *et al*., 2003]. Though intensive care and support are able to lower the death rate but patients continue to suffer from this disease for a long period of time. Some effects such as learning difficulties and behavioral problems can remain masked for several years.

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