Effect of pelleting on survival of porcine epidemic diarrhea virus–contaminated feed

Abstract

Porcine epidemic diarrhea virus (PEDV) is a heat-sensitive virus that has devastated the U.S. swine industry. Because of its heat sensitivity, we hypothesized that a steam conditioner and pellet mill mimicking traditional commercial thermal processing may mitigate PEDV infectivity. Pelleting, a common feed processing method, includes the use of steam and shear forces, resulting in increased temperature of the processed feed. Two thermal processing experiments were designed to determine if different pellet mill conditioner retention times and temperatures would impact PEDV quantity and infectivity by analysis of quantitative reverse transcription PCR and bioassay. In Exp. 1, a 3 × 3 × 2 factorial design was used with 3 pelleting temperatures (68.3, 79.4, and 90.6°C), 3 conditioning times (45, 90, or 180 s), and 2 doses of viral inoculation (low, 1 × 10 tissue culture infectious dose (the concentration used to see cytopathic effect in 50% of the cells)/g, or high, 1 × 10 tissue culture infectious dose/g). Noninoculated and PEDV-inoculated unprocessed mash were used as controls. The low-dose PEDV-infected mash had 6.8 ± 1.8 cycle threshold (Ct) greater ( < 0.05) PEDV than the high-dose mash. Regardless of time or temperature, pelleting reduced ( < 0.05) the quantity of detectable viral PEDV RNA compared with the PEDV-inoculated unprocessed mash. Fecal swabs from pigs inoculated with the PEDV-positive unprocessed mash, regardless of dose, were clinically PEDV positive from 2 to 7 d (end of the trial) after inoculation. However, if either PEDV dose of inoculated feed was pelleted at any of the 9 tested conditioning time × temperature combinations, no PEDV RNA was detected in fecal swabs or cecum content. Based on Exp. 1 results, a second experiment was developed to determine the impact of lower processing temperatures on PEDV quantity and infectivity. In Exp. 2, PEDV-inoculated feed was pelleted at 1 of 5 conditioning temperatures (37.8, 46.1, 54.4, 62.8, and 71.1°C) for 30 s. The 5 increasing processing temperatures led to feed with respective mean Ct values of 32.5, 34.6, 37.0, 36.5, and 36.7, respectively. All samples had detectable PEDV RNA. However, infectivity was detected by bioassay only in pigs from the 37.8 and 46.1°C conditioning temperatures. Experiment 2 results suggest conditioning and pelleting temperatures above 54.4°C could be effective in reducing the quantity and infectivity of PEDV in swine feed. However, additional research is needed to prevent subsequent recontamination after pelleting as it is a point-in-time mitigation step.

Evaluation of the effects of flushing feed manufacturing equipment with chemically treated rice hulls on porcine epidemic diarrhea virus cross-contamination during feed manufacturing1

“…A 1:10 dilution was performed using PBS to create 2,500 mL of 10 5 TCID 50 /mL viral inoculum. Inoculation of the feed used similar procedures as those described by Schumacher et al (2016b) and Cochrane et al (2017) . Briefly in this experiment, inoculation of feed to be used in each of the laboratory scale mixers was performed in 5-kg batches using an additional laboratory scale mixer in which 4.5 kg of PEDV-negative feed was added to the mixer and 500 mL of 10 5 TCID 50 /mL–diluted viral inoculum was added to create 5 kg of 10 4 TCID 50 /g–inoculated feed.…”

“…Bioassay procedures used were the same as those described previously ( Schumacher et al, 2016b ; Cochrane et al, 2017 ). Bioassay samples were selected after qRT-PCR analysis included a composite positive and negative control from laboratory and production-scale mixers, rice hull flush samples from the untreated, formaldehyde, and 2% MCFA flushes of the laboratory-scale mixers, as well as subsequent feed for all 4 laboratory-scale treatments ( Figure 1 ).…”

“…However, this is not practical in most current commercial feed production settings. Methods to chemically or thermally mitigate the risk of PEDV transmission in feed and feed ingredients have been investigated ( Cochrane et al, 2015 ; 2016 ; 2017 ). These methods are not universally applicable to all feed manufacturing facilities due to equipment cost or safety concerns.…”

Evaluation of the cleansing and disinfection protocol of pig-breeding premises contaminated by the porcine epidemic diarrhea virus

“…У рідких фекаліях на сонці вірус втрачає інфекційність протягом 6 год, в тіні -за 3 доби. Високі температури і прямі сонячні промені діють згубно (Jung and Chae, 2004;Thomas et al, 2014;Cochrane et al, 2017). В Україні зареєстровані і застосовуються різноманітні офіційні дезінфікуючі препарати проти інфекційних агентів різної природи.…”

Survival of porcine epidemic diarrhea virus (PEDV) in thermally treated feed ingredients and on surfaces

“…Results from other studies suggest that specific thermal processing treatments, such as spray drying (a process using dry hot air to reduce the moisture of a particle) can reduce the survival of PEDV in porcine and bovine plasma by 5 log [ 6 , 7 ]. Other research has shown that conditioning and pelleting with temperatures above 54.4 °C could be effective in reducing infectivity of PEDV in swine feed [ 8 ]. However, the sole impact of thermal processing on the inactivation kinetics of PEDV in feed is still unknown.…”