Feed Risk and Mitigation
Non-animal Origin Feed Ingredients and the Transmission of Viral Pathogens of Swine
Order Imposing Conditions in
Relation to Secondary Control Zones In Respect of ASF
Evaluation of Chemical Mitigants for Neutralizing the Risk of Foreign Animal Diseases in Contaminated Feed Ingredient
Project #: 17-187 | Investigators: Diego G. Diel and Scott Dee | Institution: South Dakota State University
The North American swine industry is under constant threat of foreign animal disease (FAD) entry. The goal of this study was to identify chemical feed additives that could be used to mitigate the risk of pathogen transmission through feed. Based on the outcome of our previous feed survival study, “high-risk” combinations of viruses and ingredients were identified. Ten mitigant candidates were selected and screened against the target pathogens. “High risk” combinations of virus and ingredient that were tested include: Senecavirus A (SVA; Soybean meal, lysine, choline and vitamin D); Porcine epidemic diarrhea virus (PEDV; Soybean meal, lysine, choline and vitamin D); Porcine reproductive and respiratory syndrome virus (PRRSV; Soybean meal and DDGS); and, Bovine herpesvirus type 1 (BoHV-1 – surrogate for pseudorabies virus [PRV]; soybean meal and soy oil cake). Results from our study show that among the 10 feed additives tested, a select group of additives presented promising efficacy against target swine pathogens. Although none of the feed additives tested completely inactivated the pathogen(s), consistent reductions in viral titers were observed when a select group of mitigants was used (KANA102 and MCFA). Interestingly, these two products showed promising results for all four viruses tested (SVA, PEDV, PRRSV and BoHV-1). Another important observation of our study is the fact that both KANA102 and MCFA are based on a blend of medium chain fatty acids. In addition to MCFA based products, Activate DA a blend of organic acids and a methionine analogue was also effective against most pathogens screened in our study. These results demonstrate that a select group of feed additives have the potential to be used as chemical mitigants to reduce viral contamination levels in feed. Further studies are warranted to assess the mechanism of action of those products and to assess their efficacy following natural ingestion of contaminated and mitigated feed.
Validation of a Low-cost Tool for Senecavirus A Detection, and Surveillance of Viral Prevalence in United States Feed Mills
Project #: 17-188 | Principal Investigator: Cassandra Jones | Institution: Kansas State University
Senecavirus A (SVA), previously known as Seneca Valley Virus, is a detrimental pathogen in the United States swine industry. Transmission is not well understood, but its similarity to foot and mouth disease virus (FMDV) suggests direct contact with people or fomites may spread the virus. Once present, viruses in feed, feed ingredients, and feed mills are difficult to mitigate. While contaminated surfaces in a feed mill have been demonstrated as a potential vector for bacterial and viral transmission, there is currently no approved method for its evaluation of viral contamination. Therefore, the objective of this Experiment 1 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 included 3 forms (inoculum, feed, or swab), 4 doses of SVA (none, low, medium, or high), and 2 storage methods (analyzed initially vs. after a freeze/thaw cycle). The SVA was added to swine feed, with 1 g reserved, and the remaining spread over a stainless steel coupon. Feed was removed, but residual feed dust remained. Next, surfaces were swabbed and samples split, with one set analyzed initially, and another frozen for 7 days, then thawed and analyzed. Results are reported as the quantity of detectable SVA as determined by threshold cycle (Ct) in qRT-PCR, where the higher the Ct, the less detectable virus was identified. The results demonstrate that sample type impacted the quantity of detectable SVA, where feed samples were approximately 8 Ct higher than the inoculum, and swab samples were approximately 4 Ct higher than feed. A freeze/thaw cycle did not impact detectable SVA compared to samples that were analyzed immediately.
In Experiment 2, the objective was to determine the prevalence and distribution of SVA in United States swine feed mills as an indicator of risk of domestic and foreign animal disease transmission through feed. A total of 375 samples were collected from 11 surfaces + one feed sample collected from 11 different feed mills manufacturing swine feed located in 8 different states. Feed mills include 5 producing both mash and pelleted feed in KS, CO, OK, NC, and IA, and 6 producing only mash feed in KS, NC, MN, IA, IN, and IL. Within a mill, locations included ingredient pit grating, fat intake inlets, exterior of pellet mill (only in feed mills with pelleting capacity), finished product boot bin, load-out auger, finished feed, floor dust in the break/control room, floor dust in receiving, floor dust in the manufacturing area, floor dust in the warehouse, worker shoe bottoms, and broom in the manufacturing area. To account for potential seasonality associated with pathogenic hazards, the same locations in feed mills were swabbed in Late Fall 2016, Winter 2016/17, and Summer 2017. Notably, no mills were manufacturing feed for SVA-positive herds at the time of analysis. Five of 375 samples analyzed positive for SVA, with Ct ranging from 37.4 to 39.9. One positive sample was collected in late Fall, while the other four positive samples were collected in Winter. No positive samples were identified in Summer. Two samples were from load-out augers, and one each from fat intake inlet, floor dust in the receiving area, and worker shoes. A sow farm being fed by the mill with SVA on worker shoes was subsequently diagnosed with SVA after the sample as collected.
These results indicate that an environmental swab can be used to detect SVA in feed, however with approximately 4 Ct less precision than analyzing feed samples directly. Furthermore, the limit of detection of SVA in environmental swabs appears to be near 10^3 TCID50/mL. Samples can be frozen prior to analysis without impacting detectable SVA RNA. Finally, SVA was not widespread throughout the swine feed mills analyzed in this experiment, but its presence in a mill may be indicative of disease risk or entry into pig populations, particularly through worker shoes.