Chapter 25: Enveloped DNA Viruses

Unlike simpler viruses, these pathogens exhibit a greater independence from host cell machinery, encoding many of their own enzymes for replication, which provides a wealth of targets for specialized antiviral therapies. The Herpesviridae family is distinguished by its unique ability to establish lifelong latency within a host following a primary infection, with the potential for periodic reactivation. These viruses are categorized into three subfamilies based on their biological traits: Alphaherpesvirinae, including Herpes Simplex Types 1 and 2 and Varicella-Zoster, which reside in nerve ganglia; Betaherpesvirinae, such as Cytomegalovirus and Human Herpesviruses 6 and 7, which often cause characteristic cell enlargement; and Gammaherpesvirinae, notably the Epstein-Barr virus, which can immortalize B cells and is linked to various malignancies like Burkitt lymphoma. The chapter details the "cascade control" of herpesvirus replication, where gene expression occurs in a strictly regulated sequence of immediate-early, delayed-early, and late stages. Significant attention is given to the pathogenesis of common conditions such as cold sores, genital herpes, chickenpox, and shingles, as well as the severe risks posed by neonatal infections and opportunistic outbreaks in immunocompromised individuals. For instance, the use of acyclovir is highlighted as a primary treatment for Herpes Simplex because it specifically targets viral DNA polymerase after being activated by a viral enzyme. Transitioning to the Poxviridae, the chapter discusses these exceptionally large and complex viruses that, uniquely for DNA viruses, complete their entire replication cycle within the host cell's cytoplasm. The most famous member, variola, the cause of smallpox, stands as a landmark in medical history as the only human disease to be completely eradicated through global vaccination efforts. The chapter concludes by reviewing other poxviruses like molluscum contagiosum and the potential of smallpox as a biological weapon, emphasizing the ongoing importance of vaccine development and public health vigilance.