Japanese encephalitis information for vets – horses

Japanese encephalitis (JE) 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 (JEV), which is a member of the Flavivirus genus. In infected humans about 1% will develop clinical disease.

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

Information for veterinarians for horses

How is Japanese encephalitis 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 JEV 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?

Note that 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, with use of appropriate personal protective equipment.

For information on disease investigations in horses, refer to the Agriculture Victoria webpage Investigation procedures for Japanese encephalitis (JE) in horses

How do I protect myself from Japanese encephalitis?

There are 2 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.