The Japanese encephalitis virus has a complex life cycle involving domestic pigs and a specific type of mosquito, Culex tritaeniorhynchus, that lives in rural rice-growing and pig-farming regions.
The mosquito breeds in flooded rice fields, marshes, and standing water around planted fields. The Japanese encephalitis virus can infect:
- Most domestic animals
After infection, the virus invades the central nervous system, including the brain and spinal cord.
Most infected people develop mild Japanese encephalitis symptoms or no symptoms at all. In people who develop a more severe disease, Japanese encephalitis usually starts as a flu-like illness, with:
Confusion and agitation can also occur in the early stage.
The disease can progress to a serious infection of the brain (encephalitis) and can be fatal in 30 percent of cases. Among the survivors, another 30 percent will have serious brain damage, which can include paralysis.
Symptoms usually appear six to eight days after the bite of an infected mosquito.
A diagnosis of Japanese encephalitis is based on tests of blood or spinal fluid.