ABSTRACT
Papillomaviruses are small, round, non-enveloped DNA viruses that infect mammals, birds and reptiles, with species- and tissue-specificity. They are one of the oldest, largest, and most diverse of the known virus families. Human papillomaviruses (HPVs), like all papillomaviruses, target the stratified squamous epithelia of the body. A subset is also able to infect the glandular epithelium of the cervix. Because culture of these viruses is not readily available, taxonomy is based on genotyping and not serotyping, which is traditionally used in virology. Viral open reading frames are arrayed in a linear fashion on only one strand of the double-stranded circular DNA genome. Due to strict species- and tissue-specificities of these viruses and their requirement for differentiating epithelium for completion of the viral life cycle, growth of HPV genotypes in the laboratory for a long time was impossible, and remains complex. In HPV-infected basal cells, papillomavirus gene expression is inhibited to near maintenance levels and the cells appear nearly normal.
