The Use of A Risk-Free In Situ Non-Animal (RISNA) Surrogate Assay for Evaluating Inactivation Strategies of African Swine Fever Virus in Feed Ingredients in Real-World Demonstrations

Abstract

African swine fever virus (ASFV) is a major foreign animal disease threat to the US swine industry. If an outbreak occurs in the United States, the swine industry could expect to see a decrease in revenue by $57 billion over a 10-year period, with additional to decreases in revenues in the corn and soybean industries. Feed ingredients, such as soybean meal, have been identified as risk factors for viral transmission to pigs. It has been hypothesized that the high temperatures and exposure to solvent, such as hexane, during solvent extraction soybean processing will inactivate viruses such as ASFV. It is also hypothesized that conditions experienced during a trans-continental trucking transport and conditions experienced in commercial warehouse storage protocols will inactive ASFV. Therefore, the objectives of this thesis were to utilize an algal virus, Emiliania huxylei virus strain 86 (EhV-86) as a surrogate for ASFV using 1) pilot solvent extraction processing plant 2) a pilot commercial trucking transport scenario and 3) pilot commercial warehouse storage protocol representing conditions used by the industry for processing, transport and storage of soybeans. Whole soybeans were experimentally inoculated with EhV-86 and exposed to hexane and a temperature range of 31-115ºC during solvent extraction processing to obtain soybean meal. Virus quantity, both total and viable, were measured using a validated viability qPCR method, in whole soybeans, conditioned soybeans, dehulled soybeans, soybean hulls, soybean flakes, air-dried solvent extracted soybean flakes, post desolventizer toaster soybean flakes, soybean meal and soybean oil. From whole soybeans to soybean meal, a 1.08 log reduction in detectable EhV-86 DNA was observed, with no detectable virus found in soybean oil. Viable EhV-86 was also present in soybean meal with a log reduction of 1.49. Additionally, conventional soybean meal (SBMC), organic soybean meal (SBMO) and swine complete feed (CF) was inoculated with EhV-86 and transported in the trailer of a commercial transport vehicle for 23 days across 29 states in various regions of the US. Totes of SBMC, SBMO and L-lysine HCl were also inoculated with EhV-86 and stored in a commercial warehouse at 20-21ºC for 35 days. Upon return for the transportation study and at the end of the warehouse study, EhV-86 was detected in all matrices and no degradation in EhV-86 viability was observed after the 23-day transportation event. Additionally, sampling sensitivity rather than virus degradation best explains the variation of virus quantity observed after 23-day transport. Storage of EhV-86 at 20-21ºC for 35 days resulted in detectable viral DNA in L-lysine HCl, SBMC and SBMO. Notably, viable virus was detected in all feed matrices yet was only present in 2 out of 6 analyzed samples in L-lysine HCl. This supports previous research findings that L-lysine HCl could potentially have antiviral properties. In conclusion, temperatures conditions during long-distance truck transport, warehouse storage, and solvent extraction processing for the production of hulls and meal are not enough to fully destroy viable EhV-86, which means that other mitigation strategies are needed to fully inactivate ASFV in feed ingredients.