Japanese encephalitis (JE) is a disease caused by a flavivirus that affects the membranes around the brain. Most JE virus infections are mild: fever and headache or without apparent symptoms, but approximately 1 in 200 infections results in severe disease characterized by rapid onset of headache, high fever, neck stiffness, disorientation, seizures, spastic paralysis, coma, and death. The case fatality rate can be as high as 60% among those with disease symptoms.
The virus causing JE is transmitted by mosquitoes. The virus circulates in birds and pigs.