Papillomaviruses are nonenveloped, double-strand DNA viruses. More than 125 HPV types are recognized, and individual types are associated with specific clinical manifestations. For example, HPV types 16 and 18 have been most strongly associated with cervical and anal cancers, causing 70-85% and ~90% of cases, respectively; HPV types 6 and 11 cause genital warts (condylomata acuminata).