Japanese encephalitis information for vets – horses

Japanese encephalitis is a mosquito-borne viral disease that can cause reproductive losses in pigs, and encephalitis in horses and very rarely in other species. Other animals do not usually show any signs, and pigs and horses may often show no signs at all. It is caused by Japanese encephalitis virus which is a member of the Flavivirus genus. In infected humans about one per cent will develop clinical disease.

Japanese encephalitis was first detected in Victoria in February 2022, with pig cases, human cases and probable horse cases.

If you suspect Japanese encephalitis in any animal immediately phone the all-hours - Emergency Animal Disease Watch Hotline on 1800 675 888.

Diagram: Japanese encephalitis disease spread pathway. A circular diagram showing the Japanese encephalitis disease spread pathway from pigs and waterfowl to mosquitoes then horses and humans.

Information for veterinarians for horses

What is Japanese Encephalitis (JE)?

Japanese encephalitis (JE) is a mosquito-borne viral disease that can cause reproductive losses and encephalitis in susceptible animal species. It is caused by Japanese encephalitis virus which is a member of the Flavivirus genus.

How is it transmitted?

The virus is primarily spread by mosquitoes feeding on infected wild birds and does not usually spread directly from animal to animal (i.e. it is not considered contagious). Certain types of mosquitoes, such as Culex sp. can become infected with JE virus and these tend to be most active at dawn and dusk.

Infected pigs do not transmit the infection to other animals but may infect mosquitoes if bitten while they still have the virus in their blood.

Other livestock such as horses, cattle, sheep and goats are ‘dead end’ hosts and cannot transmit the disease back to mosquitoes.

In general, spread of the virus is through the movement of infected mosquitoes, often over long distances due to wind dispersal and the movement of herons and egrets. Herons and egrets can carry the virus but are not affected by it.

What are the symptoms of Japanese encephalitis in horses?

In horses many cases are asymptomatic and most clinical disease is mild, however more severe encephalitis can occur which can be fatal. Signs include fever, lethargy, anorexia and neurological signs which vary with severity of the clinical disease. Neurological signs can include incoordination, difficulty swallowing, impaired vision, and rarely a hyperexcitable form occurs. Disease has also been reported in donkeys and one alpaca was confirmed with the disease in South Australia during the 2022 outbreak.

What happens if a client has a suspected case?

How do I protect myself from Japanese encephalitis?

What should be collected in the field?

N.B. clinical signs of JE in horses are also referrable to Hendra virus infection. Information on bat exposure, interstate travel and Hendra vaccination status should be obtained and, if indicated, additional samples to rule out Hendra should be taken.

Live animals with clinical signs:

  • Duplicate whole blood (EDTA) and serum samples for virus detection and serology (for serum, collect at least 7–10 mL of blood from animals in the acute phase and convalescent stage of the disease).

Collect paired serum samples 2–4 weeks apart

Dead animals preferably less than 12 hours:

  • Note: Cerebrospinal fluid (CSF) and/or tissue samples should only be taken from horses where Hendra virus has been excluded as a differential diagnosis. Place into a sterile container.


Be aware of this and other potential zoonoses – collect samples carefully and wear appropriate PPE including gloves, eye protection and a mask. The danger during sample collection is from splash or stick injuries.

Submitting samples and reports

Veterinary Diagnostic Services
AgriBio Specimen reception
Main loading dock
5 Ring Rd
La Trobe University
Bundoora 3083
Phone: (03) 9032 7515
Email: vet.diagnostics@agriculture.vic.gov.au.

The samples will undergo a suite of triage tests that are targeting Flavivirus. This will take about three days.

If the samples return a negative result at this initial stage, you will be contacted by Agriculture Victoria staff.

Positive samples will be forwarded to the CSIRO Australian Centre for Disease Preparedness for further testing which may take several months.

How do I protect myself from Japanese encephalitis?

There are two ways to protect yourself: avoiding mosquito bites and vaccination.

The Department of Health recommends people protect themselves and their families against mosquito-borne diseases:

  • Wear long, loose fitting clothes outdoors.
  • Use effective mosquito repellents containing picaridin or DEET on all exposed skin.
  • Try to limit outdoor activity if lots of mosquitoes are about.
  • Use ‘knockdown’ fly sprays and plug-in repellent devices indoors.
  • Sleep under mosquito nets treated with insecticides if you don’t have flywire screens on windows on your home or are sleeping in an untreated tent or out in the open.
  • Mosquito coils can be effective in small outdoor areas where you gather to sit or eat.
  • Remove mosquito breeding sites like stagnant water around your property.

What are the symptoms of Japanese encephalitis in humans?

A small number of people infected with JE virus may become seriously ill with encephalitis (inflammation of the brain). Other people may develop an illness with fevers, headaches and aches and pains.

Symptoms of encephalitis may include rapid onset of fever, headache, sensitivity to light, neck stiffness, vomiting, confusion or disorientation and sometimes seizures, progressing to coma. Anyone experiencing symptoms, particularly if they’ve visited regions near the border of Victoria and New South Wales or been in contact with pigs or with mosquitoes should seek urgent medical attention.

What should I do if I suspect my staff or I have Japanese encephalitis?

Any person who has been in contact with pigs and is experiencing any of the symptoms should seek urgent medical attention. Further information can be found on the Better Health website.

Is there a vaccine available for animals?

Vaccines for horses and pigs are used in some countries where the disease is endemic. No vaccines for animals are registered for use in Australia. The issues around vaccination of livestock are under consideration.

Will livestock movements be impacted?

The movement of livestock, livestock semen, horse feed and human movements are not restricted.

Page last updated: 21 May 2024