Between 1955 and 1963, more than 98 Million people were vaccinated in the U.S with the Polio vaccine known to have been contaminated with SV40. SV40 is a polyomavirus (Budgerigar Fledgling Disease) that commonly infects certain species of Asian macaques, especially the rhesus monkey. Other polyomaviruses, which are generally species-specific, include the BK and JC viruses of humans. Polyomaviruses are a genus of the papovavirus family of DNA viruses. This family also includes the papillomaviruses, of which one—human papillomavirus (HPV)—is causally associated with cervical cancer. SV40 and other polyomaviruses generally produce inapparent infection in immunocompetent members of their natural host species. SV40 and the closely related human polyomaviruses BK and JC typically reside in renal epithelial cells. These viruses can, however, spread to other tissues and produce pathological effects in immunocompromised hosts or in non-host species. In fact, the presence of SV40 in polio vaccine produced from macaque kidney cell cultures was originally identified because of the cytopathological effects of the contaminated vaccine in African green monkey kidney cell cultures (Sweet and Hilleman, 1960). As another example, the JC virus is known to cause progressive multifocal leukoencephalopathy in immunocompromised humans. Four forms of human cancer— mesothelioma, osteosarcoma, ependymoma, and non-Hodgkin's lymphoma (NHL)—have been linked to SV40 in animal studies.