Antiviral Activity of Four Commercial Tilmicosin Preparations against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV): An In Vitro Study

The efficacy of four commercial tilmicosin preparations (A, B, C and D) against type 2 porcine reproductive and respiratory syndrome virus (PRRSV), 01NP1 (Thai isolate), infection in cultured pulmonary alveolar macrophages (PAMs) was conducted in vitro. Primary PAMs were collected from four 4-week-old PRRSV-free pigs. After separately plated onto four 24-well plates, PAMs were treated separately by 4 commercial tilmicosin preparations of 2 concentrations each (0.1 mg/ml and 0.01 mg/ml). The treated PAMs were inoculated with 0.05 MOI of 01NP1 strain and were stained with PRRSV specific antibody using immunoperoxidase monolayer assay (IPMA) to evaluate the quantity of PRRSV infected cells after 12 hours post infection (HPI). Comparing to the untreated-tilmicosin PRRSV-infected PAMs, all tilmicosin-treated preparations exhibited significant virus titer reduction against 01NP1. Based on the results, 0.01 mg/ml of tilmicosin B solution exhibited the greatest PRRSV-titer reduction (65%), but was not statistically different from the others. The results indicated that tilmicosin could be one of the effective chemotherapy in reducing type 2 PRRSV infection in vitro regardless of differences in the preparations. The information obtained is of interest for practitioners for future study of implementation of tilmicosin use in PRRSV-positive farms.