Role of Transportation in Spread of Porcine Epidemic Diarrhea Virus Infection, United States

James Lowe

, Phillip Gauger, Karen Harmon, Jianqiang Zhang, Joseph Connor, Paul Yeske, Timothy Loula, Ian Levis, Luc Dufresne, and Rodger Main

Author affiliations: University of Illinois, Urbana, Illinois, USA (J. Lowe); Iowa State University, Ames, Iowa, USA (P. Gauger, K Harmon, J. Zhang, R. Main); Carthage Veterinary Service, Ltd., Carthage, Illinois (J. Connor); Swine Vet Center, P.A., St. Peter, MN, USA (P. Yeske, T. Loula); Iowa Select Farms, Iowa Falls, Iowa (I. Levis); Seaboard Foods, Kansas City, Missouri, USA (L. Dufresne)

Abstract

After porcine epidemic diarrhea virus (PEDV) was detected in the United States in 2013, we tested environmental samples from trailers in which pigs had been transported. PEDV was found in 5.2% of trailers not contaminated at arrival, , suggesting that the transport process is a source of transmission if adequate hygiene measures are not implemented.

Porcine epidemic diarrhea virus (PEDV) was detected in herds of pigs in the United States during April 2013 (1). PEDV is a member of the Cornaviridae family that produces a malabsorptive diarrhea secondary to atrophy of the small intestinal villi (2). Initial clinical cases were detected in herds in Indiana and Iowa during May 2013.The virus spread rapidly across large geographic regions; 218 cases of infection were identified in 16 states during the first 9 weeks of the outbreak (3). Subsequent testing of historical samples collected during the week of April 15, 2013 identified the index herd in Ohio (3). Veterinarians became concerned about the role that facilities where pigs are harvested for processing into food and the transportation equipment used to move pigs from farms to those facilities were playing in the spread of PEDV. These concerns were based on evidence that equipment used to transport live pigs transmits another enteric coronavirus, transmissible gastroenteritis virus, between sites in the United States (J.F. Lowe, unpub. data).

Pigs are commonly transported to harvest facilities in vehicles that have not been cleaned and disinfected between loads. Implementation of “all in–all out” sites, which are sites in which pigs are grown and all pigs in a group are removed before arrival of the next group, limits the spread of disease introduced by transport vehicles. In many cases, the risks and associated costs of disease introduced late in the growing period are thought to be less than the cost of cleaning and disinfecting vehicles. Transport vehicles are often shared by different pig owners, enabling the spread of disease across large regions.

The Study

The objective of this study was to assess the risks that harvest facilities and transport vehicles engendered in promoting the initial outbreak of a novel disease organism by estimating the incidence of trailer contamination with PEDV during the unloading process at harvest facilities. Environmental samples were collected from 575 livestock trailers before and after pigs were unloaded into holding pens, or lairages, at 6 harvest facilities (83–102 trailers per facility) located in the central United States. Samples were collected during a period of 2–3 days at each facility during June 14–20, 2013. For each trailer, the following information was collected: transport company and trailer identification, time of unloading, dock used, whether the truck driver stepped on the dock, and whether facility personnel entered the trailer. Sample collection consisted of rubbing a phosphate-buffered saline–moistened pad (Swiffer, Procter & Gamble, Cincinnati, OH, USA) over an ≈900 cm2 area of the trailer floor, 15 cm from the rear door. The pad was placed in a sterile bag (Whirl-Pac, NASCO, Fort Atkinson, WI, USA) and the liquid was collected by applying manual pressure. The liquid was transferred to a sterile tube (14mL Falcon Tube, Fisher Scientific, Chicago, IL, USA), immediately placed on ice, and maintained at 4°C during transport to the Iowa State University Veterinary diagnostic laboratory. New latex gloves were worn for each sample collection to minimize the risk for cross-contamination.