Japanese encephalitis is the most common cause of viral encephalitis in South East Asia, China the Western Pacific and India, with approx. 50,000 cases annually. It is a flavivirus transmitted by culex mosquitos which breeds in rice paddy fields. The reservoir hosts are aquatic birds, but pigs are an amplification host and therefore close domestic contact with pigs is a risk factor.

Clinical features

The majority of infection is asymptomatic.

Clinical features are headache, fever, seizures. Parkinsonian features indicate basal ganglia involvement. It can also present with acute flaccid paralysis.


Diagnosis is by serology or PCR.


Management is supportive.