Antiviral activity of Indigofera heterantha Wall. ex Brandis against Herpes Simplex Virus - type 2 (HSV-2)

Indigofera heterantha Wallich ex Brandis is a commonly distributed plant species in the western Himalayan region. Here, we report for the first time, the presence of an antiviral activity in this plant species. The activity was found to reside in the root extracts of the plant as evaluated by the in vitro screening assays, was specific to HSV-2 virus and did not show any cross-reactivity against HSV-1 virus. Results generated from the cytopathic effect inhibition and MTT assays, demonstrated that this root extract suppressed HSV-2 multiplication in a dose-dependent fashion. The extract was evaluated in a murine genital infection model against HSV-2 as a topical formulation, using acyclovir as the comparator molecule. The plant extract exhibited potent therapeutic effect against a lethal HSV-2 challenge. It also demonstrated efficacy in a prophylactic manner and was able to protect mice when applied at least 4 hours prior to viral challenge. In comparison, acyclovir acts at the replication stage of the HSV-2 life cycle and was efficacious only when treated in the therapeutic mode. Mice treated with the extract showed significant reduction in mortality as well as low or no genital lesions as compared to placebo treated and untreated control animals. In conclusion, due to its ability to act both therapeutically and prophylactically, the extract of I. heterantha can be developed as a topical microbicide or condom coating for treatment of genital herpes infection.