Japanese Encephalitis Virus (JEV)is a mosquito borne Flavavirus which is closely related to the West Nile and Saint Louis Encephalitis viruses. JEV is the most common form of viral encephalitis in Asia. There have been no reported cases of JEV originating in Africa, Europe or the Americas.
JEV infects mosquitoes that typically feed on pigs or wading birds which harbor this virus. When an infected mosquito bites a non-immune human infection can be spread to that individual. Every year there are 35,000 to 50,000 cases of Japanese Encephalitis reported to the World Health Organization. Of these reported cases there are 10,000 to 15,000 deaths annually. Of those that live, greater than fifty percent will have permanent neurologic damage. In areas where the infection is endemic most adult residents will have natural immunity but non immune travelers to those areas are at risk.
In areas where flooding irrigation is practiced (rice paddies) there are increase numbers of the vector mosquitoes and higher rates of disease. The peak incidence of infection is from June through September (China, Korea, Japan, and Eastern Russia) and the mosquitoes carrying infection typically feed from dusk to dawn.
Travelers to urban areas for brief periods of time are at lower risk. Those who are in rural areas, spend considerable time outside from dusk to dawn, or are in endemic areas for extended periods of time are at higher risk. Mosquito netting while sleeping and the use of DEET containing mosquito repellants will decrease the frequency of bites.
Vaccination for Japanese Encephalitis is recommended by the CDC for travel to endemic areas only if you are staying for extended periods or traveling to rural farming areas. Because of limited vaccine supply, and relatively high rates of adverse vaccination events, vaccination is usually not recommended for short term trips to urban areas. Vaccination consists of a two dose series at days 0, and 28, with the intent to give the last dose at least 10 days prior to departure. This vaccine, IXARO, is approved in people 17 years and older.