Emergency animal disease alert for veterinarians

Japanese encephalitis

Outbreaks of Japanese encephalitis virus (JEV) have been reported in piggeries in Queensland, New South Wales, Victoria and South Australia. One alpaca in South Australia and a small number of feral pigs in the Northern Territory have also tested positive for JEV. This is the first time the disease has been detected in southern Australia.

JE is an acute, mosquito-borne viral disease that can cause reproductive losses and encephalitis in susceptible species. Waterbirds act as natural reservoirs for the virus, and mosquitoes can spread the virus to horses, pigs and other animals. JE is a zoonotic disease meaning it can affect people, although severe disease is rare.

Waterbirds and pigs are important amplifying hosts for JE. People and horses are considered ‘dead end’ hosts - once infected they are not thought to play a role in transmitting the virus.

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.

Read specific JE information for vets in the Emergency Animal Disease Bulletin No. 125.

Stay safe

Japanese encephalitis can have a similar clinical presentation to Hendra virus (HeV) and Australian bat lyssavirus (ABLV) infection in horses, so we want to remind vets that it is important to take appropriate precautions to protect your health and the health of your clients.

When treating and investigating disease in horses, always wear appropriate personal protective equipment (PPE). Do not perform invasive investigations (including post-mortems) unless HeV has been excluded as a differential diagnosis. Serology should be used as the first line of investigation for Japanese encephalitis in horses.

Veterinarians are reminded that the HeV vaccination status of horses can sometimes be ascertained by checking the Hendra virus vaccine registry. However not all HeV vaccinated horses are on the registry and even with vaccinated horses, appropriate biosecurity precautions such as PPE should be used. No vaccine can provide 100% guaranteed protection.

Veterinarians should be mindful that horses with neurological dysfunction can be a physical danger to themselves and people around them.

For vets seeking more information on appropriate PPE, the Australian Veterinary Association has produced a Veterinary personal biosecurity and PPE guide. It details the zoonotic diseases present in Australia and how veterinary staff can use PPE to keep people safe and well. It also covers infection control, how to deal with high-risk situations and is relevant to veterinary practices of all types.

Veterinarians attendings piggeries and abattoirs, are eligible for the Japanese encephalitis vaccination. Visit the Australian Government Department of Health for information on the JEV vaccine and where you can get vaccinated.

In addition, remember to take precautions (wear personal protective equipment) while treating or taking samples from horses.

Biosecurity Queensland also has helpful Hendra virus information for veterinarians.

Reporting requirements

Veterinarians need to be alert to the signs of JE in animals.

JE in pigs

In pigs, the most common clinical signs are mummified and stillborn foetuses or piglets and weak piglets, which may have 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 oedematous, and congested testicles.

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

Preventative measures

People working or otherwise in contact with pigs, including those who may have a small herd or pet, should take steps to control mosquitoes, and continue to use effective biosecurity measures.

A guide to controlling mosquitoes around piggeries is available on the farmbiosecurity.com.au website. In addition, the National Pork Biosecurity Manual which provides in-depth detail on biosecurity practices and management in piggeries.

JE in horses

Many cases in horses are subclinical. Most clinically affected horses show only mild signs of disease. These can include pyrexia, 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.

In some cases, more severe encephalitis can occur, resulting in serious and sometimes fatal consequences.

Preventative measures

Putting a hooded rug and fly mask on your horse can help protect against mosquito bites. Stabling horses between dusk and dawn may also be beneficial as the mosquito that transmits JE feeds at night and is reluctant to enter dwellings. If the horse allows, apply a safe insect repellent.

Agriculture Victoria has more advice on protecting your horse from mosquito bites.

Human health advice

Most JE 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.

People should also try to prevent mosquito bites by using a 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 clothes; and covered footwear.

Government response

The Australian, state and territory governments are working with the pig and horse industries through the Consultative Committee on Emergency Animal Diseases (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.

The response strategy for this disease is outlined in the Japanese encephalitis AUSVETPLAN.

We also encourage you to download the Emergency animal diseases field guide for Australian veterinarians.