Papilloma virus particles. Black and white transmission electron micrograph (TEM) of a para-crystalline array of particles of the human papillomavirus (HPV). The regular arrangement of these particles is like that seen for the atoms of a crystal. Human papillomavirus is the most common sexually transmitted infection. Most sexually active men and women being exposed to the virus at some point during their lifetime. HPV is the cause of warts, growths that are commonly found on the hands, the soles of the feet, the body's mucous membranes and also on the genitals. HPV has also been linked with some skin and cervical cancers. Magnification: x10, 000, when printed 10 centimetres wide.