Japanese encephalitis

Video transcript [DOCX 23 KB]

If you are a veterinarian, please go to our Emergency animal disease alert for veterinarians page for more information and resources.

Disease situation in animals

In February 2022, Japanese encephalitis (JE) was detected and confirmed in piggeries in Victoria, Queensland and New South Wales. On 4 March, cases were detected in South Australia. There are currently more than 70 infected piggeries across the four states.

On 30 March a rare case of JE in one alpaca was confirmed in the Adelaide Plains local government area. Alpaca’s, like horses, are a dead-end host.

Also in March, the Northern Territory Government confirmed that a small number of feral pigs from the West Daly region tested positive for JE. The testing was conducted in mid-March as part of a routine animal health survey conducted by the Northern Australia Quarantine Strategy. Further surveys and testing of feral pigs, horses and other animals for JE will continue as part of the northern Australia surveillance strategy for exotic diseases.

In May 2022 the NSW Chief Veterinary Officer issued a bulletin stating that testing of horse samples had identified 26 horses with probable JE and a further 4 horses as possible cases. These horses were probably exposed to the virus during summer to mid-autumn 2022. No cases have been definitively confirmed. However, the combination of clinical signs and test results suggests that JE infection is a probable or possible cause for the disease.

NSW CVO Bulletin 23 May – Probably cases of JE in NSW horses

The locations of infected piggeries are not published due to government privacy and biosecurity requirements. The disease is widespread so regardless of where you are, protect yourself and your animals against mosquito bites.

About Japanese encephalitis

Japanese encephalitis is a viral zoonotic disease that is spread by mosquitoes. The virus can cause reproductive losses and encephalitis in pigs and horses. In rare cases, Japanese encephalitis can cause disease in people. People and horses are considered 'dead end' hosts. Once infected, they do not play a role in transmitting the virus. Pigs and some species of wild birds are amplifying hosts.

It is not known how the virus came onto mainland Australia, and it's the first time the virus has been detected in southern Australia. It is likely that the movement of infected mosquitoes or migratory waterbirds may have played a part in the virus’ spread.

In animals, signs of disease are most common in horses and pigs. Other animals can be infected but typically do not show signs of illness, such as cattle, sheep, goats, dogs, cats, bats, rodents, reptiles, amphibians and birds. Cattle, dogs, sheep, alpacas, and goats are dead end hosts that do not infect mosquitoes or people. Waterbirds such as herons and egrets (in the Ardeidae family) are the main reservoir for spreading the virus to mosquitoes. Pigs act as amplifying hosts, spreading the virus to mosquitoes.

Japanese encephalitis disease spread pathway

Japanese encephalitis disease spread pathway diagram

Japanese encephalitis virus is a nationally notifiable disease which means if you suspect an animal is showing signs of the disease, you must report it.

You can do this by contacting your local veterinarian or call the national Emergency Animal Disease Watch Hotline on 1800 675 888. This will put you in touch with your state or territory’s agriculture department.

Disease response

The Australian, state and territory governments are working with the pig and horse industries through the Consultative Committee on Emergency Animal Disease (CCEAD) in response to this outbreak. We are also working closely with human health authorities on a range of activities including surveillance and trapping, mapping and public awareness.

Mosquito trapping and control is being conducted at all infected piggeries.

Mapping of infected piggeries and suspected infected piggeries is being shared across jurisdictions and with state human health authorities. The maps will help identify potential higher risk transmission areas for communities. Locations of feral pigs, waterbirds and major watercourses will be added, along with locations of vector surveillance.

Retrospective testing of stored samples from domestic and feral pigs, horses and wildlife are being tested for JE virus. Any positive results may assist in determining when JE virus started to appear in southern locations.

A longer-term animal surveillance plan for JE virus is being developed that will include surveillance of susceptible species, including pigs (feral pigs included), horses and other animals.

In addition to movement restrictions applying to infected piggeries, there are some additional interstate movement conditions for live pigs and pig semen moving from infected areas to uninfected jurisdictions. Check with your state or territory agriculture authority.

Australia is prepared to respond to animal disease incursions with national response arrangements in place. The response strategy for this disease is outlined in the Japanese encephalitis AUSVETPLAN.

Food safety

Japanese encephalitis is not a food safety concern and commercially produced pork meat or products are safe to consume.

Signs of the disease in pigs

Japanese encephalitis is primarily spread by mosquitoes. It is not spread from pigs to people or normally from pig to pig.

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, which presents as paddling, or other neurological signs in the first six months of life. In other cases, wasting, depression or hindlimb paralysis may be seen in suckling piglets and weaners.

Adult sows do not typically show overt signs of disease. If boars are present on farm, they may experience infertility, and swollen and congested testicles.

Pig to pig transmission is rare, and on occasion can occur through infected genetic material such as pig semen.

Signs of the disease in horses

Symptoms in horses are usually mild and signs of the disease include high temperature, jaundice, lethargy, anorexia and neurological signs which can vary in severity.

Neurological signs can include incoordination, difficulty swallowing, impaired vision, and rarely, the horse becomes over excited. Reports of the disease in other species are rare, but there are cases reported in donkeys overseas.

The clinical presentation of JE is similar to other mosquito-borne diseases such as infection with West Nile/Kunjin virus, Murray Valley encephalitis virus, and Hendra virus. As Hendra virus can be transmitted directly from horses to people, it is important to take precautions and use personal protective equipment (PPE) as directed by your veterinarian, if caring for a sick horse and/or while waiting for test results.

Horses are known to be a ‘dead end host’. They do not carry enough virus in their blood to infect people or reinfect mosquitoes.

Human health advice

Most Japanese encephalitis virus infections in people are asymptomatic, however, those with severe infection (which occurs in less than one per cent of cases) may experience neck stiffness, coma, and more rarely, permanent neurological complications or death.

Encephalitis is the most serious clinical consequence of infection. Illness usually begins with symptoms such as sudden onset of fever, headache and vomiting. Anyone experiencing these symptoms should seek urgent medical attention.

People should try to prevent mosquito bites by using mosquito repellent containing picaridin, DEET or oil of lemon eucalyptus on all exposed skin and reapply every few hours.

Wear long, light coloured and loose-fitting clothing as well as covered footwear when outside. Ensure accommodation, including tents, are properly fitted with mosquito nettings or screens.

For updates and advice regarding human health, including vaccination programs, visit Australian Government Department of Health

Caring for your pigs

People working or otherwise in contact with pigs, including those who may have a small herd or pet, should take steps to control mosquitoes (see below) and protect themselves from mosquito bites. The Department of Health has detailed information for piggery workers about Japanese encephalitis.

Pig producers should be highly vigilant for signs of Japanese encephalitis in their herds and report unexpected abortions or stillbirths. JE is a nationally notifiable disease which means suspect animals must be reported to a vet or the Emergency Animal Disease Watch Hotline on 1800 675 888.

Mosquito control in piggeries

Key activities that will help reduce the mosquito load around piggeries include:

  • Monitoring for mosquitoes at the various stages of their lifecycle. This can help determine the most effective control methods and help break the breeding cycle.
    • To monitor, inspect bodies of water and containers for wrigglers, as well as areas where adult mosquitoes will rest like ceilings and walls.
  • There are non-chemical measures that can be used including removing anything in the open that is filled with water or has the potential to hold water.
  • Fill in potholes or other areas around the piggery that collect water.
  • Clear debris from gutters, downpipes, and drains around buildings so that water doesn’t pool, and trim overhanging tree branches.
  • Ensure effluent drainage is free flowing, flushed regularly and does not pool.
  • Tanks, wells or other large water containers should be sealed, or screened with 1mm mesh.
  • Reduce vegetation around the piggery to minimise areas where adult mosquitoes can rest.
  • Ensure all windows and doors are covered by well-maintained mosquito proof screens.
  • If you are opting for chemical control, be aware that:
    • chemical residues in pork are a trade and food quality risk.
    • chemicals must only be used in accordance with the directions on the label.
    • chemicals must be registered for use around pigs and approved for use against mosquitoes. It can only be used in areas that require treatment.
    • treatment should be applied by people authorised to use chemicals in accordance with state or territory training and licensing requirements.
    • chemical control can be applied to water sources, the outside of sheds and buildings, effluent ponds, and staff facilities.

You can find out more at farmbiosecurity.com.au particularly the guide to controlling mosquitoes around piggeries, and the National Pork Biosecurity Manual which provides in-depth detail on biosecurity practices and management in piggeries.

Two horses on a hillside eating grass

Caring for your horse

Putting a hooded rug and fly mask on your horse when mosquitoes are active can help protect against their bites. Where available, stabling horses between dusk and dawn may also be beneficial.

If the horse allows, apply a safe insect repellent. To apply the repellent to the horse’s face and ears, spray it onto a cloth and rub it on, avoiding around and above the eyes.

Zoos

Zoos should also practice good vector management, including avoiding pooled water sources etc.

People visiting zoos or places where there are mixed species of animals gathered, should apply mosquito repellent and wear long, loose fitting clothing.

Exports and trade

The Department of Agriculture, Water and the Environment provides the certification for live animals, meat and meat products for export to overseas markets.

The department is working with horse exporters to ensure horses meet importing country requirements for Japanese encephalitis virus (JEV). There are 12 markets that Australia exports horses to that have import requirements in place for this disease.

The department has worked with New Zealand to negotiate changes to the entry requirements for Australian horses travelling to New Zealand. Specific certification in relation to JEV is no longer required.

Work is also underway with the Australian Pesticides and Veterinary Medicines Authority (APVMA) to obtain an emergency use permit for a JEV vaccine for use in horses as part of Australia’s JEV response.

Ongoing use of a JEV vaccine in the general horse population will require a full APVMA assessment of a vaccine and will require a commercial import and distribution network.

The department will work with trading partners should any other issues arise around the export of pig meat, offal and pet food, due to this outbreak.

For media

More information

Downloadable resources

JE information in your state or territory