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Hiv/aids

Discover the latest breakthroughs, treatments, and prevention strategies for HIV/AIDS, unraveling the mysteries behind this global health challenge.
2023-05-26

USMLE Guide: HIV/AIDS

Introduction

This guide aims to provide a comprehensive overview of HIV/AIDS, a significant topic frequently tested on the United States Medical Licensing Examination (USMLE). It will cover the basics of HIV/AIDS, including epidemiology, pathophysiology, clinical presentation, diagnosis, treatment, and prevention.

Table of Contents

  1. Epidemiology
  2. Pathophysiology
  3. Clinical Presentation
  4. Diagnosis
  5. Treatment
  6. Prevention

Epidemiology

  • Human Immunodeficiency Virus (HIV) is a retrovirus that causes Acquired Immunodeficiency Syndrome (AIDS).
  • Worldwide, an estimated 38 million people are living with HIV/AIDS as of 2019.
  • Sub-Saharan Africa is the most affected region, accounting for approximately 67% of all people living with HIV/AIDS globally.
  • Transmission occurs mainly through sexual contact, blood exposure, and perinatal transmission.

Pathophysiology

  • HIV primarily targets CD4+ T lymphocytes, macrophages, and dendritic cells, leading to their destruction.
  • It enters the host cell via CD4 receptor and co-receptors (CCR5 or CXCR4) using viral envelope proteins (gp120 and gp41).
  • The viral RNA is reverse transcribed into DNA using the viral enzyme reverse transcriptase.
  • The viral DNA integrates into the host genome via the viral enzyme integrase, leading to persistent infection.
  • HIV replication occurs within the host cell, resulting in the production of new viral particles that can infect other cells.

Clinical Presentation

  • Acute HIV infection (Acute Retroviral Syndrome): Fever, lymphadenopathy, rash, myalgia, sore throat, headache, and fatigue, typically 2-4 weeks after exposure.
  • Asymptomatic (Chronic) HIV infection: May last for several years without notable symptoms.
  • AIDS: Characterized by severe immune suppression and the development of opportunistic infections, malignancies, and HIV-related complications.

Diagnosis

  • HIV screening is recommended for all individuals aged 13-64 years as part of routine care.
  • Initial screening test: Fourth-generation immunoassay (detects both HIV antigen and antibodies).
  • If positive, confirmatory test: HIV-1/HIV-2 differentiation immunoassay or nucleic acid testing (NAT).
  • Diagnosis of AIDS: CD4+ T-cell count <200 cells/μL or the presence of specific opportunistic infections/malignancies.

Treatment

  • Antiretroviral Therapy (ART) is the cornerstone of HIV management.
  • Combination therapy: Typically consists of three or more antiretroviral drugs from two or more classes (e.g., Nucleoside Reverse Transcriptase Inhibitors, Non-Nucleoside Reverse Transcriptase Inhibitors, Protease Inhibitors, Integrase Strand Transfer Inhibitors).
  • ART aims to suppress viral replication, preserve immune function, and delay disease progression.
  • Adherence to ART is crucial to prevent drug resistance.

Prevention

  • Safe sexual practices: Condom use, regular testing, and partner notification.
  • Pre-exposure prophylaxis (PrEP): Daily use of antiretroviral medication (e.g., tenofovir/emtricitabine) for individuals at high risk of HIV acquisition.
  • Post-exposure prophylaxis (PEP): Administration of antiretroviral medication within 72 hours following high-risk exposure to prevent HIV infection.
  • Needle/syringe exchange programs and harm reduction strategies to reduce transmission among people who inject drugs.
  • HIV testing and counseling to promote early detection and treatment.

Remember, this guide only provides a brief overview of HIV/AIDS. For a more in-depth understanding, refer to reputable textbooks and resources specifically tailored for the USMLE.

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