#14-239

Complete

Date Full Report Received

12/29/2016

Date Abstract Report Received

12/29/2016

Investigation

Institution:
Primary Investigator:

This project was conducted in an effort to determine the transmission risk for PEDv following on-farm composting of PEDv-positive swine mortalities. The studies performed were designed to quantify the persistence of PEDV RNA via quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) at various time-temperature combinations and in infected piglet carcasses subjected to composting.

Specific objectives of this project were to:
1.) Identify appropriate time-temperature combinations for inactivation of PEDv in compost material.
2.) Validate time-temperature combinations for PEDv inactivation in mortality compost piles.
3.) Increase confidence among pork producers and their advisors in utilizing on-farm composting as a biosecure method for disposing of PEDv-infected animals.

Identification of Time-Temperature Combinations for PEDv Inactivation (Obj. 1)
This study was conducted to quantify the persistence of PEDv RNA via quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) at various time-temperature combinations under controlled laboratory conditions.

Porcine Epidemic Diarrhea Virus was inoculated into cell culture media at 1 x 105 TCID50 per sample (1 mL sample size) at various time and temperature combinations including temperatures of 37, 45, 50, 55, 60, 65, 70°C and exposure times of 0, 24, 48, 72, 96, 120, 168 and 336 hrs. The temperature treatments were performed in incubators (Heratherm General Protocol Incubator, Thermo Fisher Scientific, Waltham, MA) maintained at the target temperatures, which were monitored for consistency throughout the trial. At each designated time point in the experiment, three cryovials were removed from the incubator and transferred to -80°C for storage until analysis by qRT-PCR. At all temperatures, virus RNA copies declined over time and with the decline most marked and rapid for temperatures of 65 and 70°C. Two of three samples had undetectable virus RNA after 336 hrs incubation at 70 °C.

Impact of Composting on Inactivation of PEDv (Obj. 2)
This study was conducted to quantify the persistence of PEDv RNA via quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) following composting of PEDV-positive piglets.

Three insulated platforms were constructed on wood pallets with internal bin dimensions of 121.92 cm (W) x 93.46 (L) cm x 97.53 cm (H). Platform walls were constructed of an outer layer of plywood (12.7 mm) and an inner layer of non-porous PolyBoard sheeting (4 mm) with foam board insulation (24 mm) placed between these layers to achieve a composite R-value of 17.3 m2KW-1. This effort was taken to simulate the linear continuation of the windrow and the insulative properties of a compacted soil base.
A single trial was conducted with a compost windrow constructed in each of the three bins using pine wood shavings at a mean moisture content of 55% w.b. Five 21-day-old piglets experimentally infected with PEDv were composted in each of the three bins over two compost cycles lasting 31 and 27 d, respectively, and temperature was monitored throughout piles during each cycle. Compost samples were collected at ten locations in each pile at the completion of the first and second compost cycles and analyzed for PEDv RNA using RT-qPCR. Material samples taken from all locations within the three piles had undetectable viral RNA following each compost cycle.
Producer Outreach (Obj. 3)
Results and recommendations regarding composting as a biosecure mortality disposal method for PEDV-infected pig carcasses have been disseminated via several routes. A UNL NebGuide (G2280: Composting of PEDv-Positive Swine Mortalities) has been published and is available online at http://extensionpublications.unl.edu/assets/html/g2280/build/g2280.htm. Results and recommendations have been incorporated into the December 2015 National Pork Board publication PEDV Resources: PEDV Brings Its Worst. Pork Checkoff Brings Its Best, available online at http://www.pork.org/wp-content/uploads/2013/11/pedvbookjan16final.pdf.