Papilloma virus. Coloured transmission electron micrograph (TEM) of human papilloma viruses (HPV), the cause of warts. They are on a fractal background. Warts commonly grow on the hands and soles of the feet, on the body's mucous membranes and on the genitals. Papilloma viruses belong to the papovavirus group, most of whose members are capable of inducing non-malignant tumours. HPV has been implicated in certain skin and cervical cancers. Magnification unknown.