These viruses are known to be the cause of warts at various sites. In addition, various HPV types are known to infect the skin, oral cavity, larynx, and anus. As is the case of HSV-2, a large proportion of HPV infections are asymptomatic and may therefore go undetected. In vitro laboratory studies have been able to isolate those fragments of the HPV DNA that are likely to be responsible for its ability to transform cells in humans, and HPV DNA fragments have been detected in tumor samples obtained from cervical cancer patients. Given the high prevalence of HPV infection relative to the incidence of cervical cancer, it is believed that HPV alone is not capable of inducing cervical cancer and that exposure to other factors, called cofactors, must be important determinants of which HPV infected women will develop the disease.
Numerous exposures are currently under investigation as possible cofactors.
However, less is known about the link between these viruses and cancers of other sites. HPV has been linked to numerous cancers, including other genital tumors, as well as skin, oral, laryngeal, and anal cancers, but causation is less firmly established.