Japanese encephalitis



  • Main vector is Culex

  • Pig, amplifier of virus. natural infection rate of 90-100%, high-titre viraemia lasts for 2-4 days

  • Human/horse: low-level and short-lived viraemia

Clinical features

  • incubation period 6-8 days

  • most asymptomatic or mild signs (1/200 - 1/2,000)

  • children and eldery at highest risk for severe disease

  • elderly: high CFR (30%)

  • Headache, high fever, stiff neck, stupor... paralysis, seizures, convulsions, coma

  • Abortion of fetus

  • Neuropsychiatric sequelae (30-50% of survivors)


  • Clinical signs...

  • Virus isolation: CSF sample, brain

  • Nucleic acid: RT-PCR (but viraemia finished when encephalitis started)

  • Antibody (HI, IFA, CF, ELISA): IgM in serum or CSF


  • No specific treatment, supportive


  • Vector control

  • Personal protection measures

  • Vaccination: equine & human

  • Live attenuated vaccine (SA-14-14-2), mainly used for equine and swine. Inactivated vaccine (JE-VAX) most commonly used for humans/travelers


  • 1870's "Summer encephalitis" epidemics

  • 1924: great epidemic in Japan (6,125 cases, >3,000 deaths)

  • 1934 first isolated (from fatal human encephalitis)

  • 1935 isolated from Culex tritaeniorhynchus, 1940-1978 epidemics in Japan, China, Korea, India

  • Vaccine developed in the 1950's, mass immunisation and cases decreased. Also lifestyle change with increased use of air-conditioning and agriculture developments in the 1960's