SHIC/FFAR JEV Research: Lessons from Australia’s Japanese Encephalitis Virus Outbreak for the US Swine Industry

By Abbey Canon

Funded by the Swine Health Information Center, in collaboration with the Foundation for Food & Agriculture Research, a study entitled, “Epidemiology of JEV in Australian Intensive Piggeries,” has recently revealed important lessons learned from the 2021-2022 Australian experience with Japanese encephalitis virus. Led by Dr. Brendan Cowled of Ausvet Pty Ltd, the study sought to understand how and why JEV spread in Australian pigs and make recommendations to assist the US industry in preparedness should JEV ever arrive in the US, a highly relevant effort due to similarity in production methods and environmental conditions for mosquito vectors in the two countries. Among outcomes were key lessons identified to help the US swine industry respond and adapt to a potential JEV outbreak. The research focused on understanding the transmission and epidemiology of JEV within farms and assessed farm-level risk factors for JEV in the Australian outbreak using quantitative and qualitative approaches for data collection and analysis.

Find a summary of project #25-053 here.

JEV is a mosquito-transmitted virus that impacts domestic swine industries and human health. It can lead to severe production impacts in commercial swine, including reproductive failure, reduced conception, abortion, mummified and stillborn piglets, shaker piglets, deformed and weak piglets, prolonged gestation and boar infertility. The virus is present in the western Pacific and Asia but has not been identified in the US, where it poses an emerging risk to pork production.

Recommendations for US industry preparedness and response to JEV

The study proposed a comprehensive suite of recommendations, detailed in the full report, covering preparedness for a possible outbreak, response to a confirmed outbreak, and strategies if JEV becomes established in the US. Key recommendations include:

The investigators have proposed a comprehensive suite of recommendations in their full report. These are divided into preparation for a possible outbreak, response to a confirmed outbreak and what to do if JEV becomes established in the US. However, they detail important recommendations that could be considered by swine farmers and industry largely in advance of any JEV outbreaks to enhance preparedness:

• Improve surveillance for JEV in the US by educating swine farmers on how to recognize JEV and how to report it.
• Explore the potential to include JEV testing in existing public health surveillance programs such as sentinel chicken flock and mosquito monitoring.
• Develop comprehensive integrated mosquito management protocols for farms. This will improve carcass quality but will also help reduce the impacts of JEV (and potentially other arboviruses) should it ever emerge in the US.
• Encourage open discussion between the swine industry, pharmaceutical industry, and EPA and/or FDA to consider pre-empt emergency registration of insecticidal treatments for use in a JEV outbreak. Collaborate with USDA for potential gaps in research to support the registration of a future swine vaccine from Australia or southeast Asia depending on JEV type.
• Continue strategic discussions between the swine industry and USDA to assess the modernization of the red book for JEV (FADPrep JEV Response plan) based on Australian experience.
• Ensure proactive engagement between public health authorities and the swine industry to share industry concerns, and to assess practical, evidence-based approaches with relevant health authorities in advance, to minimize industry impacts whilst effectively managing risk.
• In the event of JEV becoming established in the US, it may be possible to develop machine learning or other AI approaches to predict the occurrence of seasonal JEV outbreaks. These should be developed if JEV is established to provide early warnings, allowing proactive application of surveillance and control activities such as mosquito mitigation (e.g., insecticidal use) or vaccination of breeding stock (if/when a vaccine becomes available).

Quantitative Assessment

For the quantitative approach, industry, environmental, and meteorological data were used to quantify measurable disease outcomes, identify patterns, correlations and risk factors. Further, artificial intelligence (machine learning) was used to provide real time predictive models for early identification of future JEV outbreaks. The study period included in the risk factor analysis was from July 3, 2021, to March 25, 2023, well before and after the outbreak occurred in Australian piggeries.

Researchers analyzed data from six JEV-affected sow units at both the individual sow- and site-levels. Sow-level information included the site at which they were housed (sow unit), parity, farrowing and service dates, outcomes of service (i.e., farrowed, repeat mating, etc.) and details on litters produced by successful matings. The outcome variable for the site level analysis included the weekly rate of services that resulted in four or more mummies at farrowing.

Initial outbreak investigations highlighted that heterogeneity of reproductive outcomes over time could be indicative of JEV infection. Clinical prevalence rates varied from 13.4% to 43.0% in affected sows. Notably, mummified fetuses were the most common clinical sign observed. Mummified fetuses were used as the case definition for the site-level risk factor analysis as it appeared to be an accurate indicator of JEV infection. Using mummies within the analysis was also supported by the qualitative study in which the only clinical sign reported by 100% of pig veterinarians as being present was excessive mummified fetuses in a litter. The lack of consistency for other clinical signs may be due to management or reporting.