The 2022 Japanese encephalitis virus (JEV) outbreak in Australia continues to be at the forefront of producers' minds there and attract attention from around the world. As stakeholders in Australia assess what they know and what they are continuing to learn about the outbreak, international observers are addressing the potential for JEV to be discovered in currently naïve countries, bringing with it challenges to human and animal health. These topics, and others, were the focus of a recent symposium hosted by the Center for the Ecology of Infectious Disease at the University of Georgia, sponsored in part by the Swine Health Information Center. A total 156 people registered to attend the symposium (27 in-person and 129 virtual attendees) from Australia, Canada, France, Mexico, the Philippines, Singapore, and across the US. Of those, 30 were persons with USDA-affiliated agencies.
Providing the keynote address for the symposium, Mark Schipp, Australia's Chief Veterinary Officer, shared three ways in which JEV may be identified - animals showing clinical signs, humans showing clinical symptoms, and mosquito surveillance. The diagnosis of JEV in pigs on the eastern side of Australia led to further diagnoses in people and mosquitoes. Data since January 2021 show 32 confirmed cases of JEV in humans with 10 additional probable cases. Only one of those humans had exposure to pigs, per Dr. Schipp. A novel strain of genotype IV of JEV has been sequenced consistently and found to be the causative source of the 2022 outbreak.
A total of 84 pork production premises were diagnosed with JEV in eastern Australia during 2022. Interestingly, there appears to be clear alignment with some geography in Australia, i.e., the Murray River.
Climatic events impacting the Murray-Darling River Basin were considered significant as well. After a long period of drought, intense rainfall with multiple flooding events occurred recently in the eastern side of Australia. Standing water created habitat for water birds and breeding sites for mosquitoes while attracting feral pigs as well. Water bird migration up and down the east coast of Australia is believed to be important for disease spread across large areas, whereas feral pigs and mosquitos are considered less mobile, but important factors for localized amplification and transmission of JEV.
Vaccines are not yet approved for use in the Australian pig industry. Trials are underway in Australia with a goal of local vaccine development and they are also evaluating the potential use of commercial vaccines from Japan. However, historical vaccines are based on protection against JEV genotype III and efficacy against genotype IV would require confirmation.
Dr. Schipp credited their work with wildlife organizations, including Wildlife Health Australia, as invaluable. Further, he emphasized a One Health collaboration as essential; in Australia, pre-existing data sharing arrangements with public health colleagues were vital to an effective response.
Australian Pork Producer Perspective
Drs. Kirsty Richards and Bernie Gleeson with SunPork, an Australian pork production company, reviewed their experiences and learnings as well during the symposium.
The initial indications of JEV on sow farms included delayed farrowing, reduced litter size, increased return to service, late term abortions, mummified, stillborn and shaking piglets. Case studies of four affected Sun Pork herds demonstrated up to a 9% decrease in pigs weaned.
Substantial production and financial costs have occurred due to JEV and an estimated 60% of Australia's pork industry has been impacted, with a reduction of fresh pork supply from August-November this year.
There were parallel responses in the animal and human sectors with mosquito trapping and testing being conducted for surveillance early in the outbreak. Mosquito trapping varied significantly across SunPork farms, with 50,000 to 100,000 trapped at one location and just four at another.
Risk factors included standing water volume, water birds, and mosquitoes. The SunPork veterinarians said Australia is still working to identify how many bird species are competent hosts for JEV and the extent to which these interact with piggery operations. There is also uncertainty about the mosquito quantity that is needed to trigger an outbreak. Importantly, their experience showed that pig and semen movement was not a significant contributor to JEV spread.
Australian Surveillance Pivots to JEV
David Williams, lead, Diagnosis and Mammalian Infectious Disease Research Group, and colleagues at the Australian Centre for Disease Preparedness, Commonwealth Scientific and Industrial Research Organisation, were heavily involved in the laboratory diagnosis of JEV infections of animals throughout the 2022 outbreak.
In addition to human and domestic pig cases detected after the initial 2022 outbreak, active infections were detected in over 50 feral pigs in the Northern Territory of Australia. Several suspected horse cases as well as a single alpaca case were reported.
A One Health approach was undertaken to understand the molecular epidemiology of the Genotype IV outbreak strain of JEV, involving public and animal health laboratories from each of the affected Australian states. Whole genome sequences of JEV were contributed from infected domestic and feral pigs, humans and mosquitoes for phylogenetic analyses, which showed no clear geographic, temporal or host relationships between isolates. The data also supported pig movements as unlikely to have played a role in transmission.
Diagnostic testing at the Australia Centre for Disease Preparedness included the initial case confirmation from February 25, 2022, and resulted in genome characterization. Following the primary diagnosis, confirmatory testing and surveillance were launched.
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