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Understanding HIV: Mechanisms, Progression, and Treatment
HIV, or human immunodeficiency virus, primarily targets key immune cells that carry the CD4 molecule, such as macrophages, T helper cells, and dendritic cells. By attaching to these cells using the viral envelope protein GP120 and co-receptors like CCR5 or CXCR4, HIV gains entry and integrates its genetic material into the host DNA. This integration allows the virus to hijack the host’s cellular machinery to produce new viral particles, which subsequently spread infection to other immune cells.
There are two main types of HIV: HIV-1, which is the predominant strain worldwide including the United States, and HIV-2, which is much rarer and localized mainly in Western Africa and Southern Asia. The virus's ability to rapidly mutate during replication leads to the emergence of diverse strains that exhibit differences in target cell preferences—a phenomenon known as viral tropism. Such mutations complicate immune responses and disease progression, with some strains preferentially infecting macrophages and others T cells.
The clinical course of HIV infection begins with an acute phase marked by flu-like symptoms and high levels of viral replication. This is followed by a chronic or clinically latent stage, lasting years with few or no symptoms but ongoing viral replication that gradually depletes CD4 T cells. Eventually, as T cell counts fall below critical thresholds, patients experience opportunistic infections and malignancies that characterize the transition from HIV infection to acquired immunodeficiency syndrome (AIDS).
HIV transmission occurs predominantly through sexual intercourse, with male-to-male transmission being the most common in the U.S., and male-to-female transmission predominant in resource-limited regions. Other transmission routes include intravenous drug use and mother-to-child transmission via the placenta or breast milk. Less common routes include needle-stick injuries and blood transfusions. Diagnosis relies on antibody, antigen, or nucleic acid tests, with combined antibody/antigen tests recommended for early detection.
Currently, there is no cure for HIV/AIDS, but antiretroviral therapy (ART) effectively suppresses viral replication and enables the immune system to recover, helping patients live longer, healthier lives. ART consists of combinations of drugs that target different stages of the viral life cycle. Besides improving patient outcomes, ART also reduces the risk of transmitting HIV to others.