19 - Papilloma and polyoma viruses

Summary

The viruses

Human papilloma viruses (HPV) and polyoma viruses are DNA viruses and belong to the family Papovaviridae. There are over a hundred known genotypes of HPV, some of which are oncogenic.

The envelope proteins E6 and E7 are transforming proteins and associated with initiating cancer by the oncogenic HPV genotypes.

Papilloma viruses

Epidemiology

Route of spread

• Sexual: the main route of spread for genital warts is sexual, and therefore it is a sexually transmitted infection.

• Vertical: laryngeal papilloma or warts in children are usually due to transmission to the baby at the time of delivery if the mother has genital warts.

• Direct contact with infected material: usually introduced through abraded skin (e.g. sharing towels, swimming pools, walking barefoot). Common skin warts are normally transmitted by this route.

Prevalence

Infection is prevalent worldwide. Human papilloma viruses 1–4 cause skin lesions, HPV 4 typically causes plantar warts and HPV 1 papillomatous lesions on fingers and trunks. Human papilloma viruses 6 and 11 are associated with genital warts and cause respiratory papilloma in children. Human papilloma viruses 16, 18 and other higher numbered genotypes also cause genital infection, which is directly linked to cervical cancer.

Most of the HPV prevalence figures are around genital infection. Human papilloma virus infection is the commonest sexually transmitted infection, and 25–40% of women between the ages of 15–25 years have evidence of HPV infection. There are an estimated 400 million cases of genital HPV infection worldwide. It is estimated that 250000 women die of cervical cancer each year with 500000 new diagnoses each year, 80% of which occur in the developing world.