Japanese encephalitis is a reportable disease
Japanese encephalitis is a serious zoonotic disease.
There have been no active human or animal cases of Japanese encephalitis reported in WA. The presence or suspicion of Japanese encephalitis must be reported in WA.
Japanese encephalitis is an acute viral disease. It is spread by bites from mosquitos, the mosquitos become infected through biting infected waterbirds or pigs. Pigs and horses are most susceptible to Japanese encephalitis virus (JEv).
Other animals, including waterbirds (e.g. egrets and herons) which are considered to be the natural host, can be infected with the virus, but typically do not show signs of illness.
Japanese encephalitis is zoonotic and infection in humans is usually asymptomatic, however on rare occasions it can result in severe disease and even death.
Animals can be infected with JEv but they cannot transmit the virus to humans. It cannot be transmitted from human to human.
Japanese encephalitis is endemic to parts of Asia and the Torres Strait region of Australia. In 2022, JEv was detected in humans, animals and mosquitos in mainland Australia.
There is no specific treatment for Japanese encephalitis infection. Symptomatic and supportive treatment will depend on clinical signs.
Human vaccines for Japanese encephalitis are available. The WA Department of Health offers free Japanese encephalitis vaccines to eligible persons in specific areas of the Kimberley and Pilbara.
More information is available on the WA Department of Health website.
Japanese encephalitis is not a human food safety concern. Commercially produced pork meat or pork products are safe to consume.
A vaccine for Japanese encephalitis in pigs is currently being developed.
In pigs
The most common clinical signs of Japanese encephalitis in pigs are reproductive losses including abortions, mummified foetuses and stillborn or weak piglets, some with neurological signs.
Adult non-pregnant sows do not typically show obvious signs of disease.
Boars may experience fever, infertility and swollen, congested (enlarged) testicles.
Piglets infected after birth may show neurological signs such as paddling, tremors and convulsions. Wasting, depression and hindlimb paralysis is also possible.
Some endemic diseases associated with reproductive losses in pigs include porcine parvovirus and leptospirosis. Porcine brucellosis which is not present and a reportable disease in Western Australia can also present similarly to Japanese encephalitis as well as Aujeszky’s disease (pseudorabies) and porcine reproductive and respiratory syndrome (PRRS), which are exotic to Australia.
In horses
In horses, most clinical disease is mild. Many infected horses will show no clinical signs while others may show mild clinical signs such as decreased or no appetite, anorexia, lethargy, and jaundice that generally lasts for 2 to 3 days.
In more severe cases encephalitis can occur. Encephalitis can present as incoordination, difficulty swallowing, impaired vision, and rarely a hyperexcitable form can occur. Some horses with encephalitis recover but for others the disease is fatal.
Japanese encephalitis has also been reported in donkeys.
Some endemic diseases such as Murray Valley encephalitis, can present similarly to Japanese encephalitis in horses, as well as reportable diseases such as Hendra virus. Exotic diseases such as equine encephalomyelitis (Eastern, Western and Venezuelan) can also present similarly to Japanese encephalitis in horses.
How to report Japanese encephalitis
If you suspect Japanese encephalitis, see signs of disease or death consistent with Japanese encephalitis in your animals you must report it. There are 3 ways you can do this.
Any person who suspects they have been infected Japanese encephalitis must contact a medical practitioner immediately.
DPIRD provides subsidies for disease investigations in livestock where the signs are unusual or affecting several animals in the group. Ask your veterinarian about the Significant Disease Investigation Program.
Significant Disease Investigation Program
Due to the clinical similarity of Hendra virus it is appropriate precautions are taken when assessing, sampling and treating affected horses.
DPIRD recommends that producers importing pigs or porcine semen implement suitable biosecurity measures to reduce the likelihood of Japanese encephalitis virus introduction onto their property. Information on importing pigs into WA can be found on DPIRD’s Importing pigs into WA webpage.
If Japanese encephalitis is confirmed in your animals, under the Biosecurity and Agriculture Management Regulations 2013 there is a requirement on an owner/person in charge to take reasonably expected measures to reduce the likelihood of spread of a declared pest such as Japanese encephalitis virus. This includes not moving an animal that is infected with a declared pest unless the action is reasonably required for the purpose of controlling the declared pest.
How does Japanese encephalitis spread?
Japanese encephalitis is primarily spread by mosquitos (Culex sp.) feeding on infected waterbirds or pigs and then biting another animal or human.
Most animals including horses and humans are dead end hosts, which means they do not carry a blood infection that can reinfect mosquitoes, ending the virus cycle.
Waterbirds, especially those in the Ardeidae family (such as herons and egrets) are the natural host for Japanese encephalitis, meaning the virus is maintained in a cycle between waterbirds and mosquitos with infected waterbirds not showing signs of disease.
Pigs are an amplifying host meaning the virus replicates rapidly allowing feeding mosquitos to become infected and spread the virus.
Virus spread is through the movement of infected mosquitos over long distances due to wind dispersal and the movements of migratory waterbirds.
Japanese encephalitis is not spread directly between animals, with the exception of pigs where there is some evidence that pigs may become infected with Japanese encephalitis virus by direct contact with an infected pigs or via semen from an infected pig.
How can I help prevent Japanese encephalitis?
Pigs
People working with pigs, including those who may have a small herd or pet, should take steps to control mosquitoes as well as continue to use effective biosecurity measures.
- For advice on mosquito control in piggeries, please refer to the Mosquito Management in Piggeries guidelines.
- Further information on biosecurity practices can be found at the Farm Biosecurity – Pigs and in the National Pork Biosecurity Manual.
- Australian Pork Limited has several resources on protecting pigs and people against Japanese encephalitis.
- Piggeries may consider joining the national Australian Pig Industry Quality Assurance program which has a set of high biosecurity and hygiene standards for commercial piggeries.
Keeping wild birds, especially waterbirds away from piggeries is important.
Pig owners are asked to be highly vigilant for signs of Japanese encephalitis and report any suspicion of the disease.
Horses
Horse owners can put measures in place to help their horses avoid mosquito bites.
Further information can be found in the national Mosquito Management for Horses manual, along with general biosecurity recommendations on the Farm Biosecurity – Horses webpage.
Good biosecurity practices and restricting contact between pigs and wild birds is also essential.