Failure to Consider the Antigenic Diversity of Porcine Reproductive and Respiratory Syndrome (PRRS) Virus Isolates May Lead to Misdiagnosis

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is a recently identified viral disease of swine that is a significant problem in swine producing regions throughout the world. Because of the potential economic impact of PRRS on swine production, extensive resources have been expended on the development of accurate diagnostic tests and efficacious vaccines. One of the potential obstacles to the success of these efforts is antigenic diversity among PRRS virus isolates. Antigenic diversity has been demonstrated between North American and European PRRS virus field isolates by using homologous and heterologous polyclonal swine antiserum in an immunoperoxidase monolayer assay. Antigenic differences between US and European PRRS virus isolates have also been demonstrated using a panel of 3 monoclonal antibodies (MAbs) specific for the 15kD protein of the PRRS virus: SDOW 17, which was generated against the PRRS virus isolate ATCC VR-2332, and EP147 and VO17, which were generated against the PRRS virus isolate SD1. All 3 MAbs reacted, as determined by fluorescence microscopy, with 63 of 63 US isolates originating from the north-central region of the United States. Additionally, MAb SDOW17 reacted with the Lelystad PRRS virus and 56 of 56 European isolates representing 8 different countries (Denmark, France, Germany, Italy, Luxemburg, The Netherlands, Spain, and The United Kingdom). However, neither MAb EP147 nor MAb VO17 reacted with any of these European isolates. Similar observations have been made by Canadian investigators, who reported that the same panel of MAbs reacted with 10 of 10 Canadian PRRS virus isolates. These observations suggest that MAb SDOW17 could be used as a universal diagnostic reagent for the detection of PRRS virus infection in clinical specimens. However, the following report indicates that North American isolates are antigenically more diverse than previously demonstrated and that it may not be possible to rely on a single MAb for diagnostic purposes.