10 March 2022

Japanese encephalitis

This message is being sent on behalf of the Ministry for Primary Industries

Japanese encephalitis virus has recently been detected and confirmed in piggeries in the Australian states of Victoria, Queensland, New South Wales, and South Australia. Previously, the virus was known to circulate only in the Torres Strait-Northern Peninsula Area region of Queensland during the wet season. As detections are recent and span a large geographical area, the true extent of virus distribution is as yet unknown and likely to be wider than reported.

Japanese encephalitis virus is transmitted by mosquitos. Pigs and waterbirds are amplifying hosts. The virus can cause reproductive losses and encephalitis in pigs. The disease does not spread from animal to animal directly. However, horses, cattle, and people can also get the virus from mosquitos. They are dead-end hosts. They do not develop sufficient viraemia to transmit the virus back to mosquitos. Most infections in horses and humans are asymptomatic. Clinical disease is rare, but may consist of fever, neurological signs, and occasionally result in death.

Japanese encephalitis (JE) is an OIE-listed disease. The disease has never been reported in New Zealand, which means New Zealand can claim historical freedom with the OIE. Import conditions for horses from Australia are based on the historically limited distribution of JE virus in Australia. They may no longer be sufficient to reduce the risk of an infected horse being imported into New Zealand.

MPI is meeting the Australian Government to get further information about the outbreak and amend import requirements if necessary. A vaccination option has been made available as an alternative import requirement for horses from Australia. In the meantime, all horses imported from Australia are subject to a post-clearance condition to monitor for and report clinical signs of Japanese encephalitis.


What does the post-clearance condition mean?

MPI have imposed a post-clearance condition on all horses imported into New Zealand from Australia. The condition requires people responsible for the care of these horses to inspect them daily for clinical signs during the 21 days following clearance. The person in charge of the horse must report clinical signs of Japanese encephalitis to their veterinarian or directly to MPI.

What can equine veterinarians expect?

People in charge of horses could contact you about clinical signs consistent with Japanese encephalitis and arrange for an examination.

What are clinical signs of infection with Japanese encephalitis virus?

Japanese encephalitis in horses is usually mild. Signs of the disease include:

  • fever
  • jaundice
  • lethargy
  • anorexia
  • neurological signs (Neurological signs can vary in severity and include incoordination, difficulty swallowing, impaired vision, and hyperexcitability)

What do veterinarians need to do if Japanese encephalitis cannot be ruled out?

Under section 44 of the Biosecurity Act 1993, every person is obliged to report when an animal is suspected of being infected with a disease or parasite that is not already present in New Zealand.

If you are presented with a horse that has clinical signs consistent with Japanese encephalitis and you cannot rule out this (or another) exotic disease, report the suspected case to the MPI pests-and-diseases hotline on 0800 80 99 66. You will be advised of further actions to take.

What if I don’t comply with the duty to inform?

If you do not comply with the duty to inform, you may commit an offence for which you could be prosecuted. If you were convicted, you could be fined up to $5,000 (for an individual) or $15,000 (for a company).