PRRSV RNA detection in different matrices under typical storage conditions in the UK

In the UK, approximately 40% of the pig breeding herds are outdoors. To monitor their porcine reproductive and respiratory syndrome virus (PRRSV) status, blood is collected commonly from piglets around weaning. Sample collection in British outdoor pigs often occurs during the early morning hours when the piglets tend to accumulate inside sheltered areas. For practical reasons, dry cotton swabs are occasionally used for blood collection and stored at room temperature until arrival in the laboratory. Detection of PRRSV RNA is a function of viral concentration, sample type, and storage condition. To evaluate a possible impact of the sampling protocol on PRRSV species 1 (PRRSV1) detection, experimentally spiked blood samples using three dilutions of a representative PRRSV1 strain were prepared. In addition, blood samples from pigs naturally infected with PRRSV were obtained from a PRRSV-positive British herd. Spiked blood and blood from infected pigs were used to obtain sera, dry or wet (immersed in saline) polyester or cotton swabs, and FTA® cards. The different samples were stored for 24h, 48h, or 7d at 4°C or 20°C and tested by a real-time reverse transcriptase PRRSV PCR assay. Under the study conditions, the best matrix was serum (96.7%), followed by wet swabs (78%), dry swabs (61.3%), and FTA® cards (51%). Polyester swabs (76%) showed a better performance than cotton swabs (63.3%). The reduction in sensitivity obtained for swabs and FTA® cards was particularly high at low viral concentrations. The results indicate that wet polyester swabs should be used whenever possible.