Antiviral activity of Thymus vulgaris and Nepeta cataria hydrosols against porcine reproductive and respiratory syndrome virus

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is characterized by reproductive failure of sows and respiratory problems of nursery and growing pigs. Current management strategies mainly focus on preventing PRRS virus (PRRSV) infection through vaccination. However, the currently available modified live vaccines are not sufficient to eradicate the virus and do not provide complete immunity from infection. In search of agents that may be proven clinically effective against North American PRRSV (NA-PRRSV or US-PRRSV) infection, 42 natural herb hydrosols were purified and subjected to screening of their antiviral activity against two US-PRRSV strains in MARC-145 cells. Based on results obtained from cell viability test, the highest concentration showing less than 10% cytotoxicity in MARC-145 cells was chosen for each of the plant hydrosols. Antiviral activity assay indicated that both Thymus vulgaris and Nepeta cataria hydrosols reduced the PRRSV load in vitro significantly (p < 0.05). Moreover, the anti-PRRSV mechanisms of both T. vulgaris and N. cataria hydrosols were in both pre-entry and post-entry steps. These results suggest that both T. vulgaris and N. cataria hydrosols have therapeutic potential in the prophylaxis and treatment of US-PRRSV infection.