Human Papillomavirus Infections: Epidemiology, Clinical Aspects and Vaccines

Abstract

Genital Human papillomavirus infections are the commonest sexually transmitted infections worldwide. The prevalence however in cytologically normal women varies from 1.4% in Spain to over 25% in some countries South of the Sahara. Globally about 10% of women are infected with HPV. The average duration of HPV infection is 4-20 months and the majority of infected individuals will clear the infection without any clinical consequences. Persistent infection with high-risk or oncogenic types of HPV is strongly associated with the development of preinvasive and invasive lesions of the ano-genital tract, including cancer of the cervix, anus, penis, vulva and vagina. HPV 16 is the most oncogenic type and is associated with an absolute risk of high grade cervical cancer precursors of 40% after 5 years of persistent infection. HPV infection of the epithelium is very effective at evading the host immune surveillance system due to the absence of a viraemic phase, using non-lytic replication and low expression of viral proteins until late stages of epithelial differentiation. Infection of the cervix with high-risk types of HPV is a necessary although insufficient cause of cervical cancer. Important co-factors include long term use of oral contraceptives, use of tobacco, co-infection with herpes simples, Chlamydia and HIV. This article discusses both secondary and primary prevention of cervical cancer, with particular emphasis on developing countries, where 80% of cervical cancer cases are found.