Japanese encephalitis
Detections
Japanese encephalitis virus (JEV) has been detected at several piggeries in southern Queensland. There have also been recent detections in New South Wales and Victoria.
Owners of pigs and horses in Queensland should be alert for signs of Japanese encephalitis.
Report
JEV poses a risk to animal and human health, and is reportable in Queensland. If you suspect an animal is showing signs of Japanese encephalitis you must report it to:
- your local veterinarian
- Biosecurity Queensland on 13 25 23.
Japanese encephalitis is a mosquito-borne viral disease associated with reproductive losses in pigs and encephalitis (inflammation of the brain) in horses and people.
Japanese encephalitis is spread by mosquitoes. Waterbirds act as natural reservoirs for the virus, and mosquitoes can spread the virus to people, horses, pigs and other animals.
In animals, signs of disease are most common in pigs and horses. Other animals can be infected but typically do not show signs of illness. These include cattle, sheep, goats, dogs, cats, bats, rodents, reptiles, amphibians, and birds.
Japanese encephalitis is not a food safety concern. Commercially produced pork meat or pork products are safe to consume.
Scientific name
Cause
Japanese encephalitis virus (JEV), is a member of the Flavivirus genus of the family Flaviviridae.
Distribution
JEV is widely distributed in southern and Southeast Asia.
Australia experienced an outbreak of JEV in domestic pigs in 2022, with detections in over 80 piggeries in Queensland, New South Wales, Victoria and South Australia. Since then, there has been broad geographical distribution of JEV detections and the disease is considered established on the Australian mainland.
Hosts
- Waterbirds
- Pigs
- Mosquitoes, mainly Culex annulirostris
Life cycle
JEV is primarily transmitted by bites from infected mosquito vectors and is maintained in mosquito–waterbird or mosquito–waterbird–pig cycles. Australia has a number of mosquito species that are capable of transmitting the virus.
Pigs are known as 'amplifiers' of the virus as they develop levels of virus in their blood sufficient to infect mosquitoes for around 4 days.
Horses and a wide range of other species may be infected but do not develop levels of virus in their blood sufficient to infect mosquitoes, so are not involved in maintaining the disease life cycle.
JEV does not survive for long in the environment and windborne spread of the virus has not been reported.
Affected animals
- Pigs
- Horses and donkeys
- Humans
Clinical signs
Most animal infections with JEV are subclinical, meaning the animal is infected but shows no signs of disease. Among susceptible animal species, clinical disease is most commonly seen in pigs and occasionally horses—reports of disease in other species are rare.
Pigs
In pigs the most common clinical signs are mummified and stillborn or weak piglets, some with neurological signs.
Piglets infected after birth can develop encephalitis (paddling, other neurological signs) in the first 6 months of life. In other cases, wasting, depression or hindlimb paralysis may be seen in suckling piglets and weaner pigs.
Adult sows do not typically show overt signs of disease. Boars may experience infertility and oedematous, congested testicles.
Learn more about information for pig owners.
Horses
Many cases of JEV infection in horses are subclinical, meaning they are infected but show no signs of the disease.
For those cases that show signs of disease, most are mild; however, more severe encephalitis can occur which may be fatal.
Signs can include:
- fever
- jaundice
- lethargy
- anorexia
- neurological signs (incoordination, difficulty swallowing, impaired vision, hyperexcitability).
Overseas, disease has also been reported in donkeys.
Learn more about information for horse owners.
How it is spread
JEV is primarily 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 JE virus can occur.
Risk period
The main mosquito vector of JEV, Culex annulirostris, feeds at night, particularly in the periods shortly after sunset and in the early morning.
The risks of transmission of JEV in any given area are likely to vary seasonally and between years, depending on weather and other local factors.
In temperate endemic areas, infection builds up in waterbirds and then in pigs in late spring and early summer. People and horses are more commonly infected in summer and autumn.
In tropical areas, Japanese encephalitis circulates more or less continuously between mosquitoes, birds, and pigs.
In Queensland, JEV should be considered a potential risk when mosquitoes are present and therefore mosquito management should be included as part of biosecurity planning.
Control
Vaccination
As of February 2025, there are no Japanese encephalitis vaccines for animals registered for general use in Australia.
Seek medical advice about Japanese encephalitis vaccination in people.
Treatment
There is no effective treatment for Japanese encephalitis in animals.