Japanese encephalitis

Alert

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 Animal Disease Watch Hotline on 1800 675 888.

Japanese encephalitis (JE) is an acute mosquito-borne arbovirus disease associated with abortion in pigs, and inflammation of the brain in humans and horses.

Scientific name

Japanese encephalitis

Cause

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

Distribution

JEV is present in India, southeastern parts of the Russian Federation, many parts of Asia and Papua New Guinea.

Australia is considered free of the disease; however, the far north of Australia's Cape York Peninsula is considered an area at risk and seasonal incursions of JEV are occasionally detected in humans in the Torres Strait.

JEV was detected in three people in the Torres Strait Islands in 1995. Two further cases were detected in humans in Queensland in 1998, including one acquired on the Australian mainland.

Hosts

  • waterbirds
  • pigs
  • mosquitos, mainly Culex annulirostris.

Life cycle

JEV is mostly transmitted by bites from infected mosquito vectors and is maintained in mosquito–waterbird or mosquito–waterbird–pig cycles.

Waterbirds, particularly wading birds such as herons and egrets, are the main source from which transmission of JEV can occur. They are important amplifying hosts and hold enough virus in their blood to infect vectors for 1 to 7 days.

Pigs are also major amplifiers of the virus and develop levels of virus in the blood sufficient to infect vectors for around 4 days.

Outbreaks in previously unexposed pig populations typically consist of 2 cycles:

  1. 20% of pigs become infected
  2. most remaining non-immune pigs become infected approximately 1–2 weeks later.

Horses and a wide range of other species may be infected but do not develop levels of virus in the blood sufficient to infect mosquitoes, so are not involved in maintaining disease in an area.

Limited information is available on the incubation period of JE in animals. In pigs and waterbirds, it may be short with the presence of virus in the blood commencing 24 hours after inoculation. In horses, incubation periods are reported to range from 4 to 14 days. For the purposes of the OIE Terrestrial Animal Health Code, the incubation period for JE is 21 days.

Affected animals

  • horses and donkeys
  • pigs
  • humans

Clinical signs

Pigs

Infection in pigs causes reproductive disease including:

  • Stillborn, mummified, abnormal or weak piglets
  • Nervous signs in piglets including tremors and convulsions.

Horses

Infection in horses may cause severe systemic disease and encephalitis. Clinical signs vary depending on the severity of infection. They may include:

  • fever
  • decreased or no appetite
  • lethargy
  • difficulty swallowing
  • wobbliness
  • incoordination
  • hyperexcitability
  • collapse and death within 1–2 days.

Impacts

If JE were to become endemic in Australia there would be socioeconomic consequences arising from:

  • disease and deaths in people
  • disease and death of performance and recreational horses
  • commercial impacts on pig, horse and supporting industries
  • costs of vaccination and vector control programs.

How it is spread

  • Movement of infectious animals or people – particularly migratory birds
  • Movement of infected vectors – including wind dispersal

Risk period

The major Culex sp. vectors of JEV bite during the night, particularly in the period shortly after sunset and in the early morning.

In temperate endemic areas, infection builds up in waterbirds and then in pigs in late spring and early summer. Humans and horses are more commonly infected in summer and autumn.

In tropical areas, JEV circulates more or less continuously between mosquitoes, birds, and pigs.

Monitoring and action

You should monitor your pigs and horses for clinical signs consistent with JE (see symptoms).

If you believe JE is present in an animal, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Animal Disease Watch Hotline on 1800 675 888.

If you believe a person may be infected with JE, seek urgent medical advice.

In the Torres Strait, the risk of JE may be minimised by:

  • eliminating breeding sites for mosquito vectors
  • keeping domestic pigs away from residential areas
  • encouraging human personal protection, including:
    • wearing long pants, long-sleeved shirts, and enclosed shoes as appropriate
    • use of mosquito repellents, mosquito nets and window fly screens.

Control

If JE were to occur in Australia, the national policy is to control JE in domestic animal populations in order to support public health agencies and the pig and horse industries. Strategies will include:

  • early recognition and laboratory confirmation of cases
  • coordination and cooperation with public health response activities
  • epidemiological assessment to inform decisions on appropriate control measures and to establish the potential role of mosquito vectors and reservoir host species in the transmission of JEV
  • movement controls over pigs, pig semen and embryos, and other potential amplifying hosts
  • tracing and surveillance in domestic and wild animals and potential mosquito vector species
  • mosquito management in selected areas such as around piggeries
  • management of wild animal reservoir species, if warranted
  • a public awareness campaign.

Vaccination

A vaccine for horses and pigs is available in countries where the disease is endemic. No JE vaccines for animals are registered for use in Australia.

Seek medical advice about JE vaccination in people.

Treatment

There is no effective treatment for JE in animals.

Quarantine

Australia has strict import conditions for animals to prevent the entry of JE and other diseases.

In addition, the Northern Australia Quarantine Strategy (NAQS) provides an early warning system for exotic pest, weed and disease detections across northern Australia (including JE) that helps address the unique biosecurity risks facing the region.

Further information