The first virus linked to a mammalian malignancy was actually the papilloma virus of rabbits discovered by Shope in 1933. Rous established that the benign rabbit papilloma could be converted into a squamous cell carcinoma in the presence of non-viral agents such as coal tar or methylcholanthrene. This is a type of tumor that originates from epithelial cells. In humans there are at least 64 types of papilloma viruses. Most produce benign warts.
Major problem is lack of tissue culture system.
Viral genome cloned in bacteria and produced in large amounts for analysis. BPV-1 has become the model system, since can get transformation in tissue culture cells. Human Papilloma viruses. These infections are very rare in virgins. Infection is directly correlated with the number of partners a couple has had unprotected sex with.