It is a viral illness transmitted by mosquitoes. It can cause inflammation of the brain (encephalitis). It is found in most rural parts of Asian countries.
It is a rare illness. Approximately 1 in 250 people became unwell after infection.
Symptoms include high fever, convulsions, headache and neck stiffness.
1 in 300 people develop encephalitis. 20-30 % of severe cases are fatal.