In vitro Screening Antiviral Activity of Thai Medicinal Plants Against Porcine Reproductive and Respiratory Syndrome Virus

Abstract Background Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) results in economic losses in the swine industry globally. Several studies have investigated the use of plant extracts for the prevention and control of PRRS outbreaks. Thai medicinal plants may be useful for treating PRRSV infection in pigs. Therefore, we investigated the in vitro anti-PRRSV and antioxidant properties of seven Thai medicinal plants: Caesalpinia sappan Linn., Garcinia mangostana Linn., Houttuynia cordata , Perilla frutescens , Clinacanthus nutans , Phyllanthus emblica , and Tiliacora triandra .Results In the antiviral screening test, we observed that the T. triandra extract strongly inhibited the infectivity of PRRSV into MARC-145 cells [virus titer 3.5 median tissue culture infectious doses (TCID 50 )/ml (log 10 )] at 24 h post-infection, whereas the C. sappan Linn. extract strongly inhibited PRRSV replication [virus titer 2.5 TCID 50 /ml (log 10 )] at 72 h postinfection. C. sappan Linn. extract had the highest total phenol content [220.52 mM gallic acid equivalents (GAE)/g] and the lowest half-maximal inhibitory concentration [IC 50 ; 1.17 mg/ml in 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2.58 mg/ml in 2,2-azino-bis (3-ethylbenzothiazo-line-6-sulfonic acid) diammonium salt (ABTS)].Conclusion Our study showed that T. triandra could inhibit the infectivity of PRRSV, whereas C. sappan Linn was the most effective for inhibiting PRRSV replication in MARC-145 cells. This study elucidates the antiviral activities of Thai medicinal plant extracts in vivo . The result promising that the extracts of Thai medicinal plants, especially that of T. triandra and C. sappan Linn, can be developed into pharmaceutical drugs for the prevention of PRRS in pigs.