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Chapter 178. Human Papillomavirus Infections

Human papillomaviruses (HPVs) selectively infect the epithelium of skin and mucous membranes. These infections may be asymptomatic, produce warts, or be associated with a variety of both benign and malignant neoplasias. Etiologic Agent Papillomaviruses are members of the family Papillomaviridae. They are nonenveloped, measure 50–55 nm in diameter, have icosahedral capsids composed of 72 capsomeres, and contain a double-strand circular DNA genome of ~7900 base pairs. The genomic organization of all papillomaviruses is similar and consists of an early (E) region, a late (L) region, and a noncoding upstream regulatory region (URR). . | Chapter 178. Human Papillomavirus Infections Definition Human papillomaviruses HPVs selectively infect the epithelium of skin and mucous membranes. These infections may be asymptomatic produce warts or be associated with a variety of both benign and malignant neoplasias. Etiologic Agent Papillomaviruses are members of the family Papillomaviridae. They are nonenveloped measure 50-55 nm in diameter have icosahedral capsids composed of 72 capsomeres and contain a double-strand circular DNA genome of 7900 base pairs. The genomic organization of all papillomaviruses is similar and consists of an early E region a late L region and a noncoding upstream regulatory region URR . Oncogenic HPV types can immortalize human keratinocytes and this activity has been mapped to products of early genes E6 and E7. E6 protein facilitates the degradation of the p53 tumor-suppressor protein and E7 protein binds the retinoblastoma gene product and related proteins. The E1 and E2 proteins modulate viral DNA replication and regulate gene expression. The L1 gene codes for the major capsid protein which makes up 80 of the virion mass. L2 codes for a minor capsid protein. Type-specific conformational antigenic determinants are located on the virion surface. Papillomavirus types are distinguished from one another by the degree of nucleic acid sequence homology. Distinct types share 90 of their DNA sequences in L1. More than 100 HPV types are recognized and individual types are associated with specific clinical manifestations. For example HPV-1 causes plantar warts HPV-6 causes anogenital warts and HPV-16 infection can produce cervical dysplasia and invasive cervical cancer. HPVs are species-specific and have not been propagated in tissue culture or in common experimental animals. However some HPV types have been produced in human tissues implanted in immunodeficient mice. Epidemiology There are few good studies of the incidence or prevalence of human warts in well-defined populations. Common .