About 100 stains of papilloma virus infect humans. Of these, about 40 seem to prefer to take up residence in the anogenital region of the body. Most people who become infected don't show symptoms and so don't know they have the virus, though sometimes it causes genital warts. Indeed, warts in other parts of the body are also caused by papilloma viruses, though usually not the same strains that are transmitted sexually, cause genital warts, or are implicated in cervical cancer. And even the strains that do cause genital warts are almost never associated with cancer.