This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
Amanda Palowski, Cecilia Balestreri, Pedro E. Urriola, Jennifer L. G. van de Ligt, Richard Ozer, Gerald C. Shurson, and Declan C. Schroeder share the results of their recent research examining virus inactivation during feed processing systems.
Key points:
- Viable ASFV-like virus (EhV-86) was detected in soybean meal and hulls after solvent extraction processing
- The presence of viable ASFV-like virus highlights the importance of implementing proper biosecurity measures to prevent viral transmission during feed processing
Introduction
African Swine Fever Virus (ASFV) is a highly contagious and environmentally stable virus with serious implications for global swine production. The risk of ASFV introduction in the U.S. is growing, particularly with its spread in major pork-producing countries. Feed ingredients, such as soybean meal, have been identified as potential transmission routes for swine viruses. There is no global surveillance for viral contamination in feed, but mitigation strategies like thermal processing can reduce virus survival. Soybean processing methods, such as solvent extraction, may inactivate ASFV, but further study is needed to assess the effectiveness and risk of recontamination. Because ASFV is too hazardous to test in field settings, this study used Emiliania huxleyi virus 86 (EhV-86) as a safe surrogate. EhV-86 shares key structural and thermal properties with ASFV, making it an appropriate model for assessing virus survival in feed processing. The goal of this study was to evaluate whether standard solvent extraction processing of soybeans could inactivate ASFV-like viruses and to assess the potential for environmental contamination during this process.
Methods
Whole soybeans were inoculated with a high concentration (1.80 × 10⁸ virus/mL) of EhV-86 and processed in a pilot-scale soybean solvent extraction facility. Temperature, pressure, and flow rates was measured at various time points throughout the process. Samples were collected from twelve different stages of processing, including hulls, flakes, and final soybean meal, as well as from environmental locations (air, dust, surfaces). Detection of viral presence was performed using both standard qPCR (S-qPCR) and viability qPCR (V-qPCR), the latter of which distinguishes viable from non-viable viral particles. Environmental control protocols was strictly followed to avoid cross-contamination, and temperatures during processing was recorded and ranged from 31°C (87,8ºF) to 115°C (239ºF).
Results
Environmental samples taken before and after processing (including surfaces, dust, and air) showed no detectable levels of EhV-86, suggesting low risk of airborne or surface spread. However, viable virus was found throughout the soy processing stages. During the initial stages of processing (cracking, aspiration, and conditioning), the virus was detected in soybean flakes and other intermediate products. There was a slight increase in virus recovery, particularly in viable virus, in soybean flakes compared to whole soybeans. The virus was exposed to temperatures ranging from 31°C to 73°C in the preparation phase. S-qPCR results showed a viral DNA concentration range of 2.32 × 10⁷ EhV/g to 9.27 × 10⁷ EhV/g in replicate A and 3.26 × 10⁷ EhV/g to 1.19 × 10⁷ EhV/g in replicate B, with minimal changes in recovery. In the solvent extraction phase, temperatures increased to 31°C to 115°C, and the virus was also exposed to hexane. This led to a significant reduction in viral DNA (3.32-log reduction in replicate A and 3.17-log reduction in replicate B) and viable virus (1.49-log reduction in replicate A and 1.74-log reduction in replicate B). Despite these reductions, viable virus was still detected in soybean meal, with a 1.41-log reduction in replicate B and 1.49-log reduction in replicate A. Soybean oil, a by-product of the extraction process, showed no detectable viral DNA. In contrast, the highest concentration of viable virus was found in soybean hulls (up to 2.12 × 10⁷ virus/g), followed by soybean meal (up to 2.61 × 10⁶ virus/g). The most substantial reductions were observed during stages that involved higher temperatures and exposure to hexane.
Discussion
The results underscore the complexity of virus inactivation in feed processing systems.
Although high temperatures and chemical exposure led to significant reductions in viral concentration, they were not sufficient to completely eliminate viable virus, particularly in soybean meal. Soybean hulls, which are not exposed to high temperatures or solvents, posed the greatest risk, with high levels of virus remaining once these hulls are commonly used in animal feeds and can represent a high-risk factor for virus transmission in herds. Although the study used EhV-86 as a surrogate for ASFV, the results provide insight into the potential survival of ASFV during soybean processing. The findings emphasize the need for biosecurity measures to minimize the risk of viral contamination in feed ingredients, particularly in facilities that process soybeans and other agricultural products. The study supports previous laboratory findings that feed matrices can protect viruses from inactivation, emphasizing the role of physical and chemical conditions in processing efficiency.
Conclusion
This study is the first real-world demonstration showing that ASFV-like viruses can survive solvent extraction processing in soybean facilities, especially in the hull and meal components. Although over 90% of viable virus was inactivated, residual virus was still detectable, indicating a potential transmission risk. These findings highlight the importance of integrating enhanced biosecurity protocols and considering additional mitigation strategies such as increased retention time and chemical additives. Continued research, including infectivity testing through bioassays, is essential to fully understand the risks and improve feed safety protocols in the swine industry.