Antiviral activity of an extract from leaves of the tropical plant Acanthospermum hispidum.
The antiviral properties of an aqueous extract of leaves of A. hispidum were investigated. Incubation of alphaherpesviruses, pseudorabies virus (PRV) [Aujeszky virus] and bovine herpesvirus 1, during infection of MDBK [Mardin-Darby bovine kidney] cell cultures with the extract impaired productive replication of these viruses in a concentration-dependent manner. The propagation of classical swine fever virus, foot-and-mouth disease virus and vaccinia virus was not affected by the extract. MDBK cell proliferation was inhibited by the extract (IC50 value of 107±5 µl/ml). The extract concentration reducing PRV yield by 1 log10 (EC90 value) was 8±3 µl/ml. Delineation of the mechanism of the antiviral activity demonstrated inhibition of alphaherpesvirus attachment to and, to a lesser extent, penetration into the cells. Viral gene expression was not inhibited by the extract when added after entry of virions into the target cells. Reduced antiviral activity of the extract against PRV deletion mutants lacking glycoprotein C (gC) or glycoproteins gC, gE, gG and gI altogether indicated that gC alone and/or viral attachment complexes of which gC is a component constitute the target structures for A. hispidum.