Human Oncogenic Viruses: Characteristics and Prevention Strategies—Lessons Learned from Human Papillomaviruses

Approximately 12% of human cancers worldwide are associated with infectious agents, which are classified by the International Agency for Research on Cancer (IARC) as Group 1 within the agents that are carcinogenic to humans. Most of these agents are viruses. Group 1 oncogenic viruses include hepatitis C virus, hepatitis B virus (HBV), human T-cell lymphotropic virus type 1, Epstein-Barr virus, Kaposi sarcoma-associated herpesvirus, human immunodeficiency virus-1 and high-risk human papillomaviruses (HPVs). In addition, some human polyomaviruses are suspected of inducing cancer prevalently in hosts with impaired immune responses. Merkel cell polyomavirus has been associated with Merkel cell carcinoma and included by the IARC in Group 2A (i.e., probably carcinogenic to humans). Linking viruses to human cancers has allowed for the development of diagnostic, prophylactic and therapeutic measures. Vaccination significantly reduced tumours induced by two oncogenic viruses as follows: HBV and HPV. Herein, we focus on mucosal alpha HPVs, which are responsible for the highest number of cancer cases due to tumour viruses and against which effective prevention strategies have been developed to reduce the global burden of HPV-related cancers.