PSI-9 Validation of environmental swabbing to detect Senecavirus A in feed

Abstract

Abstract Senecavirus A (SVA) is an emerging virus impacting the U.S. swine herd. Environmental swabbing can help better detect the probability of feed contamination than product testing, but the detection of SVA by swabs has not yet been validated. Therefore, the objective of this experiment was to validate standardized swabbing techniques for detection of SVA. A secondary objective was to determine if a freeze/thaw cycle impacted detectable RNA. This experiment was a 3×4×2 factorial, with 3 forms (inoculum, feed, or swab), 4 doses (0, 10^3, 10^5, or 10^7 TCID50/mL SVA), and 2 storage methods (analyzed initially vs. after a freeze/thaw cycle). One mL SVA was added to 16 g of swine feed. One g reserved, and remaining 15 g spread over a 10 cm×10 cm stainless steel coupon and incubated for 15 minutes. Feed was removed, but residual feed dust remained. Next, surfaces were swabbed, swabs vortexed, and supernatants collected. Samples were split, with one set analyzed initially, and another frozen at -20°C for 7 days, then thawed and analyzed. Results are expressed as threshold cycle (Ct) from qRT-PCR analysis. There were 4 replicates per treatment. There was a sample type×SVA dose interaction (P < 0.0001; Table 1). Feed samples were approximately 8 Ct higher than the inoculum, and swab samples were approximately 4 Ct higher than feed. As expected, SVA level impacted (P < 0.0001) detectable SVA RNA. Finally, a freeze/thaw cycle did not impact (P = 0.846) detectable SVA RNA compared to samples that were analyzed immediately. In summary, this research validated that an environmental swab can be used to detect SVA in feed, however with approximately 4 Ct lower than analyzing feed samples directly. Furthermore, the limit of detection of SVA in environmental swabs appears to be near 10^3 TCID50/mL. Finally, samples can be frozen prior to analysis without impacting detectable SVA RNA.