Herpes virus and treatment. Abstract illustration of the antiviral drug famvir attacking a Herpes simplex virus, the virus that causes genital herpes. Famvir acts by specifically attacking viral DNA (Deoxyribonucleic acid) and thereby preventing the virus from replicating. The viral DNA (red and blue double helix, at centre) is enclosed in a 20-sided icosahedron coat made from protein subunits. The famvir drug reduces the pain of the ulcers caused by genital herpes. Famvir is also effective against the Herpes zoster virus, the virus that causes shingles. Famvir is manufactured by SmithKline Beecham pharmaceutics company.