Chapter 28: Retroviruses: HIV & Related Viruses

Retroviruses: HIV & Related Viruses viruses are uniquely defined by the enzyme reverse transcriptase, which enables them to reverse the traditional flow of genetic information by synthesizing DNA from an RNA template. The discussion details the complex architecture of the virion, including its lipid envelope studded with glycoproteins like gp120 and gp41, and its diploid positive-sense RNA genome. A significant portion of the material is dedicated to the HIV replication cycle, explaining the precision with which the virus targets CD4 receptors and chemokine coreceptors on immune cells before integrating its genetic material into the host genome as a stable provirus. The genomic organization is explored through the functions of major genes like gag, pol, and env, alongside essential regulatory proteins such as Tat and Rev that facilitate viral maturation and escape. Transitioning to pathology, the text describes the natural history of HIV, from acute viremia and seroconversion to the prolonged clinical latency phase where viral replication persists within lymphoid tissues. It defines the progression to Acquired Immune Deficiency Syndrome (AIDS) by the severe depletion of T-lymphocytes and the emergence of life-threatening opportunistic infections and malignancies, such as Kaposi sarcoma and various lymphomas. Furthermore, the chapter reviews diagnostic strategies—ranging from p24 antigen detection to quantitative nucleic acid testing—and the implementation of Highly Active Antiretroviral Therapy (HAART), which uses multi-drug combinations to suppress viral loads. Finally, it examines HTLV-1, highlighting its role in causing adult T-cell leukemia and chronic neurological conditions, underscoring the ongoing challenges in treating these persistent infections.