Japanese encephalitis

What is JEV?

Japanese encephalitis virus is a mosquito borne virus, a flavivirus, that may infect a range of species including waterbirds, pigs, horses and donkeys, cattle, sheep, goats, water buffalo, chickens and others. These animals act as sentinels (or indicators), highlighting the presence of the disease in the environment.

Infection with Japanese encephalitis virus (JEV) is a serious, emergency animal (exotic) disease of animals. It is notifiable in Australia, meaning any suspected cases need to be reported immediately.

How is it characterised?

Japanese encephalitis virus (JEV) is a mosquito-borne viral disease, which is maintained in nature by transmission cycles involving Culex sp. mosquitoes, certain species of wild and domestic birds and pigs. Humans  may also become infected resulting in encephalitis (inflammation of the brain) and death in severe cases.

While Japanese encephalitis has an incubation period of up to 21 days in pigs it is typically 1-3 days and horses 4-14 days. Refer to the NSW Health fact sheet for more information on infection and illness in people.

Adult non-pregnant sows show no obvious signs of infection. However, JE is associated with reproductive failure in pigs, with 50–70% losses reported in affected populations:

  • Pregnant sows and gilts may abort, produce mummified or malformed foetuses, or give birth to stillborn or weak piglets at term,
  • Infertility in boars - this is most commonly temporary but may be permanent if the boar is severely affected.
  • Nervous signs such as tremors and convulsions are occasionally seen in pigs up to 6 months of age.

Other species can be infected with JE and clinical signs are usually mild or not obvious. Occasionally, horses can show neurological  signs including severe encephalitis.

How do I report it?

If you suspect JE in pigs, you must report it to your Local Land Services District Veterinarian immediately on 1300 795 299 or call the 24-hour Emergency Animal Disease Hotline on 1800 675 888.

If you suspect JE in horses, you must report it to your veterinarian or call the 24-hour Emergency Animal Disease Hotline on 1800 675 888.

How is it spread?

Few species play a significant role in transmission, mainly waterbirds and pigs, and few species show clinical signs of disease.

The primary mechanism of spread of JEV between hosts is by bites from infected mosquito vectors. Transmission is believed to be maintained in mosquito–waterbird or mosquito–waterbird–pig cycles.

Waterbirds, particularly wading birds, such as herons and egrets, are the main natural reservoirs of JEV and are important amplifying hosts.

Pigs (feral and domestic) develop high levels of infection and are also major amplifiers of the virus.

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

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

Horses are a dead-end host, while they can become infected with JE, they cannot pass on infection to other horses or people. People do not get infected from horses.

How are suspect JEV cases investigated

If pig illness or deaths are consistent with disease due to JEV, contact the Emergency Animal Disease Watch Hotline on 1800 675 888 for advice.

For further information refer to Emergency animal diseases field guide for Australian veterinarians, the AUSVETPLAN – Japanese encephalitis and Japanese encephalitis information for veterinarians.

More information on clinical presentation and investigation can be found at:

Where is it found?

JEV is present in India, south-eastern parts of Russia, 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. Most recently, a human case was detected on the Tiwi Islands in 2021.

What are the impacts?

There would be considerable impact on both human health, animal industries as well as socio- economic impacts.

How is it treated?

The national policy is to control JE in domestic animal populations to support public health agencies and the pig industry. 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

There is no effective treatment for JE in animals in Australia.

The best way to protect your pigs and horses is by developing and implementing an integrated mosquito management plan. This involves targeting all stages of the mosquito life cycle to break the breeding cycle.

Seek medical advice about JE in people.

In NSW, all pigs (pets and commercial) need to be tagged or branded to assist with identification as part of the National Livestock Identification System (NLIS). The NLIS enhances Australia's ability to quickly contain a major zoonotic disease incident to help protect our livestock industries and communities.