Introduction
African swine fever (ASF) is considered a major threat to the pig industry, animal health, and food security worldwide (Guinat et al., 2016). The causative agent, ASF virus (ASFV) is a complex, enveloped DNA virus of the Asfarviridae family with high tenacity (Alonso et al., 2018). Given the stability of ASFV under a wide range of ambient conditions, farmers and other stakeholders are concerned about ASFV transmission via feed and feed ingredients, but unfortunately, the data basis is very limited. Against this background, the European Food Safety Authority (EFSA) defined research gaps regarding the potential for ASFV transmission through contaminated feed and feed materials (Alvarez et al., 2019). Of special interest could be feed with compounds of porcine origin, e.g. spray dried porcine plasma (SDPP). SDPP is extensively used in pig starter diets and consistently improves growth performance, and survival, especially under stressful conditions like pathogen challenge (Perez-Bosque et al., 2016). So far, there are very few studies on ASFV inactivation in re-contaminated porcine plasma. Kalmar et al. (2018) investigated a combination of physical and chemical processing conditions of liquid plasma, i.e. heat treatment (48°C), alkaline conditions (pH 10.2), and addition of peroxide (102.9 mM H2O2). This treatment led to an ASFV titer reduction of 4.17 log10 TCID50/ml after 10 min. Polo et al. (2019) reported a titer reduction of 4.62 log10 TCID50/ml after UV-C irradiation of liquid porcine plasma at a dose of 3000 J/l. The spray drying process itself with an inlet temperature of 200°C and a temperature of 80°C throughout substance led to an ASFV titer reduction of 4.11 log10 TCID50/ml (Blázquez et al., 2018). The above-mentioned studies addressed mainly contaminations that affected the raw materials, i.e. plasma originating from infected pigs. However, concerns were also raised with regard to possible re-contamination scenarios.
The objective of the presented study was therefore to determine the stability of ASFV on re-contaminated SDPP after production when stored for different time periods (0, 7, 14, 21, 28 and 35 days) at two different temperatures (4°C and room temperature). For this purpose, commercial SDPP granules were contaminated with high titer ASFV (106 50% haemadsorbing doses per ml [HAD50/ml]). Successful contamination was demonstrated via real-time PCR analysis. Three samples per time point and temperature condition were subjected to a blind passage on peripheral blood mononuclear cell (PBMC) derived macrophages and to subsequent haemadsorption tests (HAT) to determine residual infectivity.