Theoretical and experimental approaches to estimate the usefulness of pooled serum samples for the diagnosis of postweaning multisystemic wasting syndrome

Classical postweaning multisystemic wasting syndrome (PMWS) diagnosis is based on postmortem findings (histopathology plus viral detection in lymphoid tissues). Because one of the major differences between PMWS-affected and nonaffected pigs is Porcine circovirus-2 (PCV-2) load in serum and tissues, real-time quantitative polymerase chain reaction (qPCR) has been suggested as a potential diagnostic technique for the disease. The objective of the present study was to assess the applicability of qPCR to quantify PCV-2 loads in pooled serum samples as an easy-to-use PMWS diagnostic tool at the herd level. The experimental design included two simulation studies with several serum pool sizes from pigs already screened for PMWS (by histopathology and detection of PCV-2 by qPCR). Several qPCR thresholds were defined and validated with experimental pools created in the laboratory. Quantitative PCR on pooled serum samples did not result in a sufficiently reliable alternate method to the classical PMWS diagnosis method based on individual clinical, histopathological, and PCV-2 detection criteria. However, serum pools seemed to be an alternative at a low economic cost for the quantification of PCV-2 loads in suspicious herds. A targeted (including only clinically diseased animals) sampling approach did not give better estimates compared with a random sampling approach.