Shahrekord University of Medical Sciences Journal of Herbmed Pharmacology 2345-5004 4 3 2015 07 01 In vitro evaluation of antiviral activity of essential oil from Zataria multiflora Boiss. against Newcastle disease virus 71 74 EN Ali Mohammadi Najmeh Mosleh Tahoora Shomali Maryam Ahmadi Sara Sabetghadam Journal Article Introduction: The study aimed to investigate the antiviral activity of Zataria multiflora (ZM) essential oil against Newcastle disease virus (NDV) on Vero cells. Methods: The cytotoxicity of ZM essential oil was evaluated by MTT assay. Cells were infected with 100 TCID50 of a field isolate of virulent NDV (JF820294.1). ZM essential oil at concentrations of 1/5000, 1/25 000, 1/125 000 or 1/625 000 was added at different times of infection: 60 minutes pre infection, simultaneously and 60 minutes post infection. Cells were evaluated morphologically. The TCID50, neutralizing index (NI) and HA titer were determined. Results: Cells treated with ZM essential oil in all concentrations 1 hour before or after infection, showed CPE similar to control virus cells. In simultaneous use, cells treated with 1/5000 concentration of the essential oil, remained morphologically normal. TCID50 values of all treatments were very close to that of control virus except for simultaneous administration at concentration of 1/5000 which was about 1000 folds lower. Virus titer in different treatments was exactly the same as control virus titer in Haemagglutination (HA) test. Conclusion: ZM essential oil has some antiviral activity on NDV in vitro, which is possibly by destruction of virus infectivity or inhibition of early phases of viral proliferation cycle.