Japanese Encephalitis Virus (JEV) is a flavivirus maintained in a zoonotic cycle which involves pigs, birds and Culex species of mosquitoes causing fatal encephalitis endemic most of Asia and as far as Australia from its putative origin in Indonesia and Malaysia. The principle vector is Culex mosquito, most important being Culex tritaenorhynchus, present in greatest density in rainy season (June to November) Humans are accidental dead-end-hosts as they do not develop a level of viraemia sufficient to infect mosquitoes. The natural cycle of JEV consists of pig-mosquito-pig or bird-mosquito-bird and pigs serve as a biological amplifiers and reservoirs. The risk for Japanese encephalitis varies by appropriate ecological conditions and season to cause epidemics and epizootics. Disease control by vaccination is considered to be most effective. The Envelope (E) protein is dominant antigen including immunologic responses in infected host and eliciting virus neutralizing antibodies. Large scale immunization of susceptible human population is highly important to prevent this deadly infection. Attempts are being made to develop enhanced vaccines using the recombinant DNA technology. Since the existing inactivated, live attenuated or killed vaccines have side effects such as neurological disorders and systemic hypersensitivity, DNA based vaccines might aid the purpose of combating against JEV which are presently under clinical trials. Protection at personal level would help to reduce the incidence of the disease. In India vaccination against Japanese encephalitis are administered in areas where the disease is hyper-endemic."
