Japanese B encephalitis

Last reviewed 01/2018

Japanese encephalitis (JE) is a mosquito-borne (Culex tritaeniorhynchus) infection caused by a single-serotype RNA flavivirus (1).

• tend to occur in wet areas (rice paddies and other open water sources) where Culex tritaeniorhynchus (and similar species) lay eggs
• pigs and aquatic birds are important as principal vertebrate amplifying hosts
• is not transmitted from person to person (2)
• humans rarely develops enough viremia to infect feeding mosquitoes (dead-end JE virus hosts)
• <1% of human JEV infections result in JE (1)   

The infection risk to travellers is 1:5000/month if living more than a month in rural areas during the season

It rarely (1 in 300 cases) proceeds to encephalitis but tends to be more serious in non-immune older patients. It is a greatly-feared disease, fatal in 25% of cases and causing parkinsonism, paralysis and retardation in 30-70% of survivors. It also causes abortion and fetal death.

Japanese and other children are routinely immunised.

Reference:

• (1) Campbell GL et al. Estimated global incidence of Japanese encephalitis: a systematic review. Bull World Health Organ. 2011;89(10):766-74
• (2) Immunisation Against Infectious Disease - "The Green Book". Chapter 20 Japanese encephalitis (January 2013)