African swine fever (ASF) is the most significant foreign animal disease threat to the US pork industry. ASF virus (ASFV) not only causes high case fatality rates of infected pigs but is a trade-limiting disease resulting in significant economic losses to pork exports. Over the last 4 years, ASFV has spread rapidly into new countries and regions of the world, including China in 2018 and the Dominican Republic in 2021. The virus is resistant to environmental degradation and maintains infectivity in swine feed ingredients exposed to transoceanic shipment conditions. As ASFV is transmissible through consumption of contaminated feed, imported feed and ingredients from ASFV-positive countries are a risk for introduction and spread of the virus to US swine. Storage of high-risk feed ingredients to allow for virus degradation over time has been recommended as a mitigation strategy to reduce this risk. However, holding times for feed at risk for ASFV contamination have historically been calculated based on conditions with fluctuating temperature and humidity. The objective of this study was to evaluate the infectivity of ASFV Georgia 2007 over time in feed stored at stable environmental temperatures to develop holding time recommendations. Three feed matrices (complete feed, soybean meal, ground corncobs) along with positive and negative controls were exposed to three environmental storage temperatures (40°F, 68°F, 95°F) for up to 1 year. Additionally, medium chain fatty acid and formaldehyde-based feed additives were evaluated for temperature-dependent efficacy against ASFV in stored feed. ASFV DNA was highly stable across feed matrices and was detectable by qPCR in almost all samples through the conclusion of each study. Infectious ASFV was most stable in soybean meal, maintaining infectivity for as long or longer than ASFV infectivity in laboratory media. All three feed additives tested in this study reduced ASFV infectivity in stored complete feed. This data helps define risk mitigation of ASFV introduction and transmission through feed ingredients. Further, this data is being used to characterize ASFV decay patterns for time by temperature feed storage. This study underscores the longevity of ASFV survival in contaminated soybean meal and supports the concept of feed quarantine for targeted high-risk ingredients as part of swine biosecurity programs.
Key Findings:
• ASFV viability was dependent on feed ingredient, being most stable in soybean meal, followed by complete feed, and was least stable in ground corncob particles
• ASFV DNA was highly stable, being detected in almost all feed samples for up to 1 year when stored at 40°F and 68°F
• ASFV remained infectious in soybean meal for at least 112 days at 40°F, at least 21 days at 68°F, and at least 7 days at 95°F
• Storage time of feed ingredients at risk for ASFV contamination is temperature-dependent with longer times required for feed stored at colder temperatures
