ABSTRACT
This chapter describes the immunodeficiency viruses and papillomaviruses. Retroviruses are a large family of RNA viruses possessing reverse transcriptase and integrase enzymes, which enable them to transcribe their RNA genome into DNA that can be integrated into the host chromosome. Certain types of human papillomaviruses, which are said to be "high-risk," can be causative agents in cervical and other anogenital cancers; cervical cancer is a leading cause of cancer deaths in women worldwide. The life cycle of papillomaviruses is played out within layers of differentiating epithelial tissue in which the virus can be viewed as holding in check its activities in order to conform to the cellular program. Papillomaviruses invade the basal layer that contains a small number of stem cells, probably through a lesion in the epithelium. Infection is thought to begin with invasion of the slowly proliferating cells rather than of the nondividing cells. The chapter also presents an overview of the key concepts discussed in this book.
