Epidemiology of Viruses Associated with Human Cancer

Abstract

This chapter focuses on the current knowledge regarding the transmission of four groups of viruses with well-documented links to human cancer, i.e., the herpesviruses (particularly Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8)), the papovaviruses (primarily human papillomavirus (HPV)), the hepatitis viruses, and the retroviruses (human T-cell lymphotropic virus type I (HTLV-I)), noting the apparent risk factors for the progression of these common infections to cancer. As with most herpesviruses, infection of children with EBV usually either is asymptomatic or produces mild disease, but if primary infection is delayed until puberty or afterwards, infectious mononucleosis (IM) is a frequent outcome, accounting for the observation that IM is predominantly a disease of upper socioeconomic groups. HHV-8 (also called Kaposi's sarcoma-associated herpesvirus [KSHV]) is, like EBV, classified as a gammaherpesvirus. HPV have the greatest public health relevance of the human Papovaviridae. HPV are widely accepted to be the principal causative agents in the development of cervical cancer, the second most common malignancy in women worldwide. The chapter focuses on HBV, HCV, and HDV, which have been implicated as etiologic agents of primary hepatocellular carcinoma (HCC). HTLV-I through undetermined mechanisms is also associated with various nonmalignant conditions. The development of serologic assays facilitated the descriptive epidemiology of HTLV-I and revealed that the virus clustered in areas where the disease was found. A major focus of research remains on understanding the cofactors that operate in the presence of the viruses increasing the risk of cancer development, so that these too can be avoided.