Japanese encephalitis

Japanese encephalitis is a notifiable disease

Under Queensland legislation, if you suspect the presence of this disease, you must report it to Biosecurity Queensland.

Call us  13 25 23 or
Emergency Disease Watch Hotline  1800 675 888

Overview

Cause

Japanese encephalitis (JE) virus is a member of the genus Flavivirus of the family Flaviviridae.

Description

JE was first isolated in Japan in 1935 although the disease was known as early as 1871. It is an acute arbovirus disease associated with abortion in pigs and encephalitis in humans and horses. Water birds are the reservoir for the virus population. The main mosquito vector in Queensland is considered to be Culex annulirostris.

Where the disease occurs

JE occurs in widely dispersed areas in eastern Asia, including Papua New Guinea and Indonesia.

Of concern to Australia was the introduction of the virus into the Torres Strait islands in 1995 with two fatal cases of encephalitis in people and the Australian mainland in the western Cape York Peninsula in 1998. The concern is that migratory birds or newly introduced mosquito vectors could carry the disease further south in Australia.

The disease in animals

Waterbirds (herons and egrets) are the main reservoir for spreading the JE virus. Pigs and waterbirds are important amplifying hosts.

In pigs, clinical signs are mainly confined to the pregnant sow, which may abort or produce mummified foetuses, stillborn or weak piglets. Pigs up to six months old may show neurological signs indicative of encephalitis.

Infection in horses may cause severe and often fatal encephalitis, but horses are considered an end-host as they don't develop sufficient virus to infect mosquitoes.

Unapparent infections occur in cattle, sheep, goats, dogs, cats, rodents, snakes and frogs. Several species of bat are susceptible to JE. The susceptibility of Australian native fauna is not known.

Spread of the disease

Transmission of JE only occurs by biting insects.

Control of the disease

In the Torres Strait where JE is an annual risk, preventive measures are aimed at:

  • elimination of breeding sites for mosquito vectors
  • not having domestic pigs near residential areas. In the Torres Strait authorities advise having communal piggeries at least 3 km from communities if pigs must be kept
  • the use of mosquito repellents, mosquito nets and other methods of personal protection.

In countries where the disease is endemic, a vaccine for horses and pigs is available.

The disease in people

In countries where JE is endemic, about 50,000 human cases occur annually and about 25% are fatal. Most human cases are asymptomatic. Severe neurological signs associated with encephalitis occur in up to 5% of cases. In pregnant women infected during the first or second trimester, spontaneous abortion and foetal death have been documented. People are considered an end host since they do not manufacture sufficient virus particles to infect mosquitoes.

A vaccine is available for people and has been registered for use in Australia.

Further information

Last updated 06 February 2013