Dose-dependent reduction in dengue viral RNA and viral proteins synthesis were also observed upon treatment with increasing concentrations of Lanatoside C. Time of addition study indicated that Lanatoside C inhibits the early processes of the dengue virus replication cycle. Furthermore, Lanatoside C can effectively inhibit all four serotypes of dengue virus, flavivirus Kunjin, alphavirus Chikungunya and Sindbis virus as well as the human enterovirus 71. Lanatoside C possesses broad spectrum antiviral activity against several groups of positive-sense RNA viruses.