Diagnostic Performance of a Reverse Transcription-Polymerase Chain Reaction Test for Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome (PRRS) virus first appeared in swine in Canada in the late 1970s, in the United States in the mid 1980s, and in Europe in 1990.23 Since that time, PRRS virus infection has become endemic in most pork-producing areas of the world. Although infection is frequently subclinical, PRRS virus plays a significant role in swine health, as reflected in the number of cases submitted to veterinary diagnostic laboratories located in swine-dense areas. For instance, in 1998 the Iowa State University Veterinary Diagnostic Laboratory (ISU-VDL) performed 90,608 serologic tests for the detection of PRRS virus antibody (J. Zimmerman, personal communication), and among diagnostic cases involving swine, 83% of samples (5,026/6,023) submitted for virus isolation included a request for isolation of PRRS virus (K.-J. Yoon, personal communication). Economically, PRRS is generally perceived to be the most significant infectious disease of swine in North America. Over the last several years, the economic impact of PRRS virus on swine production has stimulated a substantial investment of research resources into the search for effective disease control strategies. The development of accurate and rapid diagnostic assays has been an essential part of this effort. Numerous procedures have been developed and implemented for the diagnosis of PRRS, including serum antibody assays, virus isolation techniques, and antigen detection and visualization in tissues by immunohistochemistry or immunofluorescence microscopy.24 In addition, a number of polymerase chain reaction (PCR) assays and in situ hybridization techniques have been developed for the detection of PRRS virus RNA in clinical specimens, including serum, semen, and tissues.4,9–12,16,17 The transfer of PCR technology into the diagnostic setting has been of particular interest to diagnosticians and swine practitioners. Generally, PCR is considered to offer distinct advantages over other techniques, including faster availability of results, higher diagnostic sensitivity, and higher diagnostic specificity. At the present time, however, documentation of the specific diagnostic performance characteristics of PCR assays is sparse. Here, we report observations on the diagnostic performance of a PCR assay for the detection of PRRS virus. The original intent of this research was to use a reverse transcription-nested PCR (RT-nPCR) to detect PRRS virus genomic material in field samples collected from 20 commercial swine herds. Field samples (n 5 756) were submit-