This flavivirus is a very important viral pathogen throughout Southeast Asia and into India. As many as 50,000 people may be infected each year.

Japanese encephalitis virus (JEV) is transmitted by Culex spp. mosquitoes. The major reservoir hosts are shore birds, such as herons and egrets, and pigs. These species replicate the virus to high enough titer to serve as a source for re-infection of mosquitoes. Horses, and very rarely cattle, may develop encephalitis, but they, like humans, are dead- end hosts.

JEV infection in pigs:

• abortion in pregnant sows and neonatal death
  • rarely, clinical signs of encephalitis in young piglets

JEV infection in humans:

Infection is most common in unvaccinated children and travelers to the region. In contrast, indigenous adults are likely to have been exposed and to have become immune as they age.

• The majority of initial infections are subclinical - only 1 in 300 people develop acute encephalitis. However, of those that do, up to 25% may die. In addition, up to 70% of subclinically infected individuals develop post-infection neuropsychiatric disorders, so the impact of this disease goes well beyond the acute infection stage.

Prevention of JEV infections:

Children in endemic areas have been routinely vaccinated since the 1960's. Swine are also vaccinated in some parts of the region in order to reduce their role as a reservoir of the virus in nature.

References:
Acha, P.N. and B. Szyfres (Eds.). 1989. Zoonoses and Communicable Diseases Common to Man and Animals. Pan American Health Organization; Washington, D.C.

Benenson, A.S. (Ed.). 1995. Control of Communicable Diseases Manual. American Public Health Assoc.; Washington, D.C.

Monath, T.P. 1995. Flaviviruses, in: Principles and Practice of Infectious Diseases (Eds. G.L. Mandel, J.E. Bennett and R. Dolin), pp. 1465-1474. Churchill Livingston, Inc.; New York, NY.