Stability of porcine reproductive and respiratory syndrome virus and antibody in swine oral fluid

Objective: To evaluate the stability of porcine reproductive and respiratory syndrome virus (PRRSV) and anti-PRRSV antibodies in oral fluid as a function of time and temperature. Materials and methods: A 4-L pool of swine oral fluid was collected from 16-week-old finisher pigs. To ensure uniform, quantifiable levels of virus and antibody over time, 4 mL of PRRSV isolate ISU-P containing 1 × 1012 RNA copies per mL and 10 mL of concentrated hyperimmune anti-PRRSV antibodies were added to the pool. The pool was then divided into three equal portions: no treatment, chlorhexidine digluconate at 0.01% by volume, and isothiazolinone at 3 ppm. Each treatment was tested in triplicate at each of five temperatures (-20°C, 4°C, 10°C, 20°C, and 30°C). Samples were removed at specific intervals (0, 12, 24, 48, 72, 144, 216, and 288 hours), stored at -80°C, and then assayed for PRRSV RNA; IgM, IgA, and IgG PRRSV-specific antibody; and culturable bacteria per mL. Results: The stabilities of anti-PRRSV antibody and detectable PRRSV were temperature-dependent, with antimicrobial treatment providing no improvements in stability at lower temperatures. Both virus and antibody were stable at ≤ 10°C over 12 days of storage. Implication: Conventional serum storage protocols (freezing or refrigeration at 4°C) preserves PRRSV and anti-PRRSV antibody in oral-fluid diagnostic samples without the use of preservatives.