Japanese encephalitis

Japanese encephalitis is category 1 restricted matter.

Under Queensland legislation, if you suspect the presence of this disease in any species of animal, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Disease Watch Hotline on 1800 675 888.

Japanese encephalitis (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.

Cause

A member of the genus Flavivirus of the family Flaviviridae.

Distribution in Queensland

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

The virus was introduced into the Torres Strait Islands in 1995 (with 2 fatal cases of encephalitis in humans) and to the Australian mainland in the western Cape York Peninsula in 1998. The concern for Australia is that migratory birds or newly introduced mosquito vectors could carry the disease further south.

Affected animals

horses; pigs; cattle; sheep; goats; dogs; cats; rodents; snakes; frogs; humans

Symptoms

Pigs

Clinical signs are mainly confined to the pregnant sow, which may abort or produce mummified foetuses, or stillborn, or weak piglets. Pigs up to 6 months old may show neurological signs indicative of encephalitis.

Horses

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

Other animals

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

Humans

In countries where Japanese encephalitis 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.

How it is spread

Transmission only occurs by biting insects. The main mosquito vector in Queensland is considered to be Culex annulirostris.

Waterbirds (herons and egrets) are the main reservoir for spreading the virus.

Pigs and waterbirds are important amplifying hosts.

Control

Prevention

Japanese encephalitis is an annual risk in the Torres Strait. Preventive measures aim to:

  • eliminate breeding sites for mosquito vectors
  • keep domestic pigs away from residential areas. Authorities in the Torres Strait recommend that communal piggeries are kept at least 3km from human dwellings, if pigs must be kept at all
  • encourage personal protection through the use of mosquito repellents, mosquito nets and other methods.

Vaccination

A vaccine for horses and pigs is available in countries where the disease is widespread.

More information