A computer-generated 3D space-filling model of the structure of small virus-like particles assembled from the late major capsid protein L1 of the human papillomavirus 16. Model based upon Protein Database 1DZL. Papillomaviruses are a group of over 100 DNA-based virus types that infect the skin and mucous membranes of humans and certain animals. Some high-risk HPV types such as Type 16 shown here, may cause abnormal Pap tests and also lead to cancer of the cervix, vulva, vagina, anus, or penis. HPV infection is a necessary factor in the development of nearly all cases of cervical cancer. Other HPV types are 'low-risk' types, and they may cause mild Pap test abnormalities or genital warts. Genital HPV infection is a sexually transmitted disease (STD) that is caused by human papillomavirus (HPV). Recently a vaccine called Gardasil has recently been developed to help prevent diseases that are caused by human papillomavirus, (HPV).