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

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.

A review of strategies to impact swine feed biosecurity

“…The challenge in loss of sensitivity is not confined to PEDV. We recently observed a similar CT sensitivity loss between liquid inoculum and dry feed with Senecavirus A (SVA) (Sardella et al, 2019). Furthermore, Dee et al (2018) reported a loss in sensitivity between stock virus and various ingredients or complete feed for SVA, BVDV (surrogate for CSFV), PRRSV, and ASFV.…”

“…The challenge in loss of sensitivity is not confined to PEDV. We recently observed a similar CT sensitivity loss between liquid inoculum and dry feed with Senecavirus A (SVA) (Sardella et al ., 2019). Furthermore, Dee et al .…”

Reviewing the risk of feed as a vehicle for swine pathogen transmission

“…A decision tree has been developed by the Swine Health Information Center to help facilities identify high-risk ingredients (Swine Health Information Center, 2018). (Sardella et al, 2019;. This type of environmental monitoring can establish baseline Enterobacteriaceae levels in facilities, and identify poor hygiene areas that are likely to be risk points for pathogen entry.…”