In early 2022, Japanese encephalitis virus (JEV) expanded into new regions of Australia, affecting over 80 swine breeding farms and causing significant production losses. Having never been detected in swine in the US, JEV poses an emerging transboundary threat to domestic sow herds susceptible to viral infection. As part of industry preparedness activities for JEV, SHIC funded an economic assessment to explore the potential impacts for introduction and establishment of JEV in the US. Dr. Liz Wagstrom, Wagstrom Consulting, led the investigation, alongside a team of economists and production veterinarians, to gather production data during the Australian outbreak and develop a prediction for production losses due to reproductive outcomes during a potential US incursion.
Now complete, the full domestic JEV incursion economic assessment white paper can be accessed here. Authors estimated that 32% of the US sow herd would be at-risk for JEV infection and that resulting sow herd losses would range from 1-2% of production. Assuming no increase in prices due to the diminished output, economic losses to the US pork industry would be between $306 million and $612 million. While the study did not assess the impact on boar studs or changes in demand for pork and pork products, the predicted production impact for US swine herds supports the need for continued JEV prevention and preparedness activities.
The 2022 outbreak of JEV genotype IV spread rapidly across new geographic regions in Australia affecting breeding swine herds and causing reproductive failure, delayed farrowing, stillbirths, mummified fetuses, abortions, and weak shaker piglets. Additional clinical signs were noted for infected boar studs including orchitis, decreased sperm number (in some cases progressing to semen with no sperm) or motility in semen, and abnormal spermatozoa. Between February 25 and March 3, 2022, JEV infection in pigs was confirmed in four Australian states. By mid-2022, more than 80 pig farms located over much of the southern and eastern parts of Australia were infected. Since the last identified JEV infection in Australian swine was in a single gilt in November 2022, no additional JEV infections in Australian domestic swine have been identified during 2023 – 2024. Through interviews with Australian veterinarians and analysis of production data, it was estimated that approximately 60% of Australia’s sow herds were impacted with overall production losses ranging from 3% – 6%.
As part of the economic assessment for a potential JEV incursion to the US, the investigative team evaluated differences between the US and Australian pork industries. Compared to the US inventory of 72.2 million swine on over 60,000 farms, the Australian pig industry is smaller with an inventory of 2.4 million swine on 4,300 piggeries. Further, farm ventilation type was compared as it had been previously hypothesized as a risk factor for infection during the Australian outbreak. Australian veterinarians estimated that of the 90% of sows raised in indoor confinement, only 10% are housed in mechanically ventilated facilities. This contrasts with US sow herds predominantly raised in mechanically ventilated facilities including filtered barns, which are believed to have lowered risk for mosquito exposure. For US herds, ventilation type varies by production region and was considered when assessing overall percentage of sows impacted by a potential JEV incursion.