110: Japanese Encephalitis

Classification: ICD-9 062.0; ICD-10 A83.0

Syndromes and synonyms: Japanese B encephalitis.

Agent: Japanese encephalitis virus (JEV), an enveloped, single-stranded, positive sense RNA flavivirus. It is divided into five antigenic groups and four genotypes, which may be linked to differences in virulence.

Reservoir: Wading birds (Ardeidae) and domestic pigs which amplify the virus asymptomatically; mosquitoes by transovarial transmission and possibly overwintering adults.

Vector: Mosquito species that breed in rice fields and marshes, principally Culex tritaenorhynchus group; also C. gelidus and C. vishnui.

Transmission: By mosquito bite.

Cycle: Only ardeid birds and pigs have a sufficient viremia to infect mosquitoes. The mosquito picks up the virus from the blood of a viremic host. After a few days, the virus reaches the salivary glands and is injected into the next host when bitten. Humans are incidental and dead-end hosts as viremia does not reach sufficient levels to infect mosquitoes.

Incubation period: 6–16 days.

Clinical findings

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