Papillomaviridae

Papillomaviridae is a family of non-enveloped, icosahedral double-stranded DNA viruses that infect vertebrate epithelia. The virions are small, about 55 nanometers in diameter, and contain a circular genome of roughly 8 kilobases. The genome encodes early genes involved in replication and transcription, including E1 and E2, and often E6 and E7 in certain human papillomaviruses, as well as late genes encoding the major and minor capsid proteins, L1 and L2. The noncoding long control region contains origins of replication and regulatory elements.

Replication occurs in differentiating keratinocytes of stratified epithelia. Infected basal cells maintain viral DNA at low copy numbers; as cells migrate and differentiate, the virus amplifies and expresses late genes in the upper epithelial layers, culminating in virion assembly and shedding from desquamating cells.

Papillomaviridae comprises multiple genera, including Alphapapillomavirus, Betapapillomavirus and Gammapapillomavirus, among others such as Mu- and Nu-papillomaviruses. The family infects a wide range of hosts, particularly mammals, birds and reptiles, with many papillomaviruses adapted to specific tissues, such as mucosal or cutaneous epithelia. The viruses exhibit considerable genetic diversity and a tendency toward host and tissue specificity.

Clinical relevance includes a spectrum of infections in humans and animals. Mucosal Alphapapillomavirus types include high-risk HPV types associated with cervical and other anogenital cancers, while low-risk types can cause genital warts or other lesions. Cutaneous papillomaviruses cause common warts and other skin lesions. Vaccines targeting several high-risk HPV types (for example, Gardasil 9) have reduced disease burden. Diagnosis commonly relies on PCR-based typing and sequencing.