Porcine reproductive and respiratory syndrome (PRRS) diagnostics: Interpretation and limitations

Porcine reproductive and respiratory syndrome virus (PRRSV) has been a major pathogen associated with swine disease. Attempts to control and better understand this disease have led to the extensive implementation of diagnostic assays. Techniques commonly used include enzyme-linked immunosorbent assay, indirect fluorescent antibody, serum neutralization, polymerase chain reaction, and nucleotide sequencing. These assays provide information about the PRRSV status of an animal or herd, but if not interpreted correctly, erroneous conclusions may be drawn and inappropriate decisions made in attempts to control PRRSV. Factors such as laboratory variation, reagents used in the assay, protocol variation, and technical limitations should all be considered when interpreting diagnostic results. The diagnostic assays based on nucleotide sequence also appear to be greatly misunderstood in the industry and do not provide insight into either PRRSV isolate virulence or vaccine selection. This manuscript attempts to review general diagnostic assay principles, provide insight into assay limitations, and provide recommendations on proper use of assays and interpretation of results.