46 The Distribution of Porcine Epidemic Diarrhea Virus, Porcine Reproductive and Respiratory Syndrome Virus, and Seneca Valley Virus 1 Inoculated Feed After Chemical Mitigation to Flush a Feed Mill

Abstract

Abstract Contaminated feed is a route of virus transmission between feed mills and swine farms. To reduce the risk of transmission, an understanding of the virus distribution and mitigation strategies are needed. The objective was to evaluate the distribution in the feed and environment of a feed mill of porcine epidemic diarrhea virus (PEDV), porcine reproductive and respiratory syndrome virus (PRRSV), and Seneca Valley virus-1 (SVV1) inoculated feed before and after the use of chemical mitigants. A 22.7 kg batch of feed was inoculated with PEDV, PRRSV, and SVV1 and ran through a mixer, bucket elevator, conditioner, pellet die, and cooler. Following the virus-inoculated batch, a flush treatment of either 1) ground corn (GC), 2) GC + 1.5% liquid formaldehyde (LF; SalCURB LF Liquid, Kemin, Des Moines, IA), 3) GC + 1.5% LF + 25% abrasive material (LF-BB; SalCURB; Shell & Bone Builder, Iowa Limestone Company, Urbandale, IA) 4) double flush – GC + 25% abrasive material follow by GC +1.5% LF (2F; Shell & Bone Builder; SalCURB) or 5) dry formaldehyde (DF; SalCURB F2 Dry, Kemin, Des Moines, IA) was manufactured, followed by 3 virus-free batches. Feed and environmental samples were taken from each piece of equipment. Dust samples were taken from the inoculated, flush, and final batches from non-feed contact surfaces. Samples were analyzed via a triplex PCR at the Kansas State Veterinary Diagnostic Laboratory. Cycle threshold and proportion PCR positive were analyzed using SAS GLIMMIXv9.4 (SAS, Inc., Cary, NC). A treatment×batch×location interaction was not observed (P > 0.05) in feed for any of the viruses. A thermal processing×treatment×batch interaction was observed (P < 0.05) for PEDV, PRRSV, and SVV1. The implementation of a flush, either chemical or physical, in combination with thermal processing led to reduced quantities (P < 0.05) of viral RNA for PEDV and PRRSV as compared with the positive pre-thermal feed. Chemically mitigated flushes reduced the quantity of SVV1 RNA in the flush and first post-flush batch more than GC pre-thermal processing (P < 0.05) with similar quantities of viral RNA post-thermal processing. In the post-thermal environmental samples, a batch×treatment interaction was observed for PEDV and SVV1, driven by increased quantities of viral RNA (P < 0.05) in the positive batch with no detectable RNA in the flush and post-flush batches. Decreasing quantities of viral RNA (P < 0.05) in dust were observed between the positive and last batch for all viruses; however, SVV1 RNA was still detectable in the dust following the last batch in all treatments. The use of chemical mitigants and thermal processing reduced the quantity of viral RNA for PEDV, PRRSV, and SVV1; however, viral presence was still observed in dust on non-feed contact surfaces which could pose as a source of contamination if re-introduced into finished feed.