Effect of temperature, relative humidity, and time on the detection of swine RNA viruses (PRRSV, PEDV, IAV) inoculated onto filter papers

Introduction: Filter papers have a long history of use in diagnostic specimen collection and storage, e.g., Guthrie cards, and recently, as leave-in-place environmental samplers in laboratory animal colonies. Paper offers a practical, low-cost solution to sample handling, but there is little data on the effect of temperature (T), relative humidity (RH), and time on target detection. The aim of this study was to evaluate the effect of T, RH, and time on the recovery of PRRSV, PEDV, and IAV RNA from 4 paper products under defined environmental conditions. Methods: In Study 1, 4 paper products were inoculated with each virus and subjected to one of 9 combinations of T (5 °C, 20 °C, 35 °C) × RH (< 20%, 40 - 65%, > 75%) for 0 to 7 days. In Study 2, paper products 3 and 4 were inoculated with PRRSV and PEDV and held at 20 °C × RH (< 20%, 40 - 65%, > 75%) for 0 to 28 days. The effect of environmental conditions on detectable viral RNA was determined by RT-qPCR with results normalized to efficiency-standardized Cqs (ECqs). Results and discussion: In Study 1, recovery of viral RNA differed among viruses and by temperature, but paper products performed similarly. In Study 2, both viruses were recovered from both paper products through the 28-day sampling period. However, higher RH (≥ 40% RH) was associated with increased loss of detectable RNA. At < 20% RH, no decay was observed for either virus on either paper. Overall, our findings indicate that multiple paper products are suitable for storage of viral specimens; albeit the optimal storage conditions would include low RH and low temperature.