In vitro antiviral activity of neem (Azardirachta indica L.) bark extract against herpes simplex virus type-1 infection.

Herpes simplex virus type 1 (HSV-1) causes significant health problems from periodical skin and corneal lesions to encephalitis. We report here that an aqueous extract preparation from the barks of neem plant Azardirachta indica acts as a potent entry inhibitor against HSV-1 infection into natural target cells. The neem bark extract (NBE) significantly blocked HSV-1 entry into cells at concentrations ranging from 50 to 100 microg/ml. The blocking activity of NBE was observed when the extract was pre-incubated with the virus but not with the target cells, suggesting a direct antiHSV-1 property of the neem bark. Further, virions treated with NBE failed to bind the cells which implicate a role of NBE as an attachment step blocker. Cells treated with NBE also inhibited HSV-1 glycoprotein-mediated cell-cell fusion and polykaryocytes formation suggesting an additional role of NBE at the viral fusion step. These findings open a potential new avenue for the development of NBE as a novel antiherpetic microbicide.