Diagnostic testing for swine respiratory viruses using oral fluids in Saskatchewan

Abstract

Porcine respiratory disease complex (PRDC) is one of the most economically significant clinical conditions in growing pigs worldwide. The clinical signs of PRDC are typical for respiratory diseases and the most common pathogens that play a role in PRDC are: porcine reproductive and respiratory disease syndrome virus (PRRSV), influenza A virus (IAV-S) and porcine circovirus type 2 (PCV2). The primary purpose of this study is to assess the detection frequency of these three viruses on selected farms within Saskatchewan using oral fluids (OF). Additional purposes are to examine the monthly trends of each of the three respiratory viruses, to evaluate the positive frequency of OF and NSSW by sample, barn and month in grower pigs for IAV-S detection. Furthermore, the purpose was to assess the ability to detect the specific genetic types of IAV-S strains circulating in SK while comparing results of IAV-S testing for OF and NSSW samples. Validation of real-time PCR procedures for PRRSV, IAV-S, and PCV2, was conducted using ten-fold dilution series within OF and sterile water with each virus. The amplification efficiencies for manual and machine extraction of these dilutions for PRRSV, IAV-S, and PCV2, were calculated. For the main project, we collected six OF samples per month from each of ten and nine grower- finisher farms for five consecutive months over the winters of 2013-2014 and 2014-2015, respectively (509 samples total). Real-time PCR was used to detect viral nucleic acid in all OF samples. Barn-level prevalence was similar between the two years for all three pathogens. However, detection frequency of three pathogens changed over the period of collection, and the pathogens detected varied month-to-month. Furthermore, more than one pathogen was found in six farms, and all three pathogens were found in one farm in both years. NSSW received with some of the OF samples were tested for IAV-S and detection of IAV-S RNA was more frequent with NSSW than OF. In conclusion, NSSW has a high positive frequency for IAV-S detection compared to OF by sample, barn and month. Moreover, there was no effect of the season for sampling and currently circulating influenza viruses of these Saskatchewan swine farms are alpha H1N1, 2009 pandemic H1N1, and Cluster IV H3N2.