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Around Australia, an outbreak of Japanese encephalitis virus has highlighted how a changing climate may be contributing to an increasing threat of new and emerging diseases to both animals and people—and the pivotal role veterinarians are playing in the disease response. By Phil Tucak
In February 2022, an outbreak of Japanese encephalitis virus was detected in piggeries in Victoria, Queensland and New South Wales. Within weeks, further cases of the disease were detected in piggeries in South Australia, and in other animals—including in an alpaca in South Australia and in feral pigs in the Northern Territory.
Usually considered a tropical disease, Japanese encephalitis virus is spread by mosquitos, with numbers of the vector thought to have been exacerbated by recent extreme wet weather and flood events in some states. This outbreak is considered the first time that the disease has occurred in southern Australia.
“It is worrying that we are seeing Japanese encephalitis virus in southern Australia. It indicates that the host and vector are able to live and prosper across a large area of highly populated South-Eastern Australia. It could be an indicator that other vector borne diseases may also penetrate or become established in areas of Australia traditionally thought to be exempt from vector borne disease,” says Dr Mark Schipp, Australia’s chief veterinary officer.
“Japanese encephalitis virus is always present in northern Australia, particularly in the Torres Strait. But what is unusual this year is its appearance in southern Australia and in such an extensive fashion. At this stage we believe the extended warm and wet conditions brought about by the La Nina weather pattern which resulted in widespread flooding, encouraged waterbirds—the natural reservoir host for the virus, and mosquitos to move south.”
The Australian Government has declared this Japanese encephalitis virus outbreak a ‘communicable disease incident of national significance’, and is undertaking retrospective surveillance of archived blood samples from pigs, horses, wildlife and insects to try to pinpoint when and where the virus made this significant advance into southern Australia.
Japanese encephalitis virus can cause reproductive losses and encephalitis in pigs and horses, and in rare cases the virus can cause disease in people. South Australian-based pig health and production veterinarian Dr Jonathon Bartsch witnessed the outbreak unfold firsthand.
“The initial clinical signs noted in the pig herds we were involved with included an increased number of stillborn and mummified piglets, especially in sows which farrowed after their due date. The typical presentation on our farms has been a late farrowing sow giving birth to a largely dead and mummified litter, in some cases unaffected littermates are completely normal,” explains Dr Bartsch.
“Retrospectively, we believe one farm’s initial presentation was increased neurological pigs at birth as mummified piglets followed at the following farrowing four weeks later. The farms which we have been directly involved with have so far had a reduction in the number of viable piglets born of between 2-20 per cent.”
As the veterinary response to the outbreak swung into action, Dr Bartsch says a commonsense approach was followed by veterinary practitioners, government agencies and industry.
“I believe we are quite fortunate the issue initially presented in the latter half of summer rather than the start of summer. The main concerns I have to date are whether this will become endemic. Emotional fatigue on farm is a significant issue, as in my experience the vast majority of the animals affected are newborn piglets,” says Dr Bartsch.
In Victoria, experienced pig veterinarian Dr Trish Holyoake runs Holyoake Veterinary Consulting, and she shares concerns that Japanese encephalitis virus “will become endemic, and there’s uncertainty around how long reproductive losses will last in herds that are currently affected. Since we first observed cases in mid-February, there’s been an increase in the stillbirth rate of around 25 per cent in some herds and litters where half the piglets were born with nervous signs such as tremors and the other half dead,” says Dr Holyoake.
“What’s been important to the veterinary response is good communication with clients regarding the clinical signs to look out for, validating reporting of cases and encouraging clients to protect themselves and their livestock.”
Practising good mosquito control is being strongly encouraged by veterinarians and government agencies as the best form of protection against being exposed to the disease, and vaccination against Japanese encephalitis virus has been prioritised for those working in identified higher risk settings such as piggeries.
Mosquitos are the vectors for multiple infectious diseases which pose a threat to Australia’s livestock industries, including lumpy skin disease of cattle, a disease not currently present here but is spreading in the region to Australia’s north. Australia’s chief vet is keen to highlight that vigilance by veterinarians and livestock producers is vital.
“Lumpy skin disease is one of a number of vector-borne diseases approaching Australia. The challenge with lumpy skin disease is that it can be carried and transmitted by any biting insect, so potentially it could be blown into Australia, or carried in the hold of a vessel or aircraft,” says Dr Schipp.
“Something has changed in our environment which has driven disease in wildlife and livestock which has consequences for human and animal health. Veterinarians are uniquely placed to see the full context of this challenging disease environment.”
Japanese encephalitis virus and lumpy skin disease are both notifiable diseases, and veterinarians should report any suspicions of such diseases to the Emergency Animal Disease Watch Hotline on 1800 675 888.