Japanese encephalitis is a viral disease spread by mosquitoes. It is associated with inflammation of the brain and hence termed encephalitis. This severe and potentially life-threatening disease is rare.

The illness occurs in two forms - a primary form and a secondary form. The primary form of the disease is more serious, while the secondary form is more common. But because of the milder nature of secondary encephalitis, more cases of primary encephalitis are seen.

The disease is transferred from infected animals - usually pigs and wading birds - to humans. Japanese encephalitis is the leading cause of viral encephalitis in Asia with 30-50,000 cases reported annually.