AIDS and Opportunistic Infections Overview

HIV Overview

• HIV isolated in 1983; initial recognized case in 1981.
• Disease causes profound immunosuppression leading to opportunistic infections, non-Hodgkin lymphoma (NHL), and neurological manifestations.

Pathogenesis

• HIV primarily targets the immune system and central nervous system (CNS).
• Two types of HIV:
  • HIV-1: most common strain globally.
  • HIV-2: predominantly found in West Africa.
• Genetic variability includes three major groups:
  • M (main), with subtypes A to K.
  • O (outlier).
  • N (non-M, non-O).
• In Ethiopia, subtype C is the dominant strain.

Epidemiology

• 20 million deaths and approximately 40 million individuals currently living with HIV, mainly in sub-Saharan Africa.
• Half of the infected population is aged between 15-24 years, with a majority unaware of their infection status.
• Nearly all infected individuals progress to AIDS and eventual death.

HIV Transmission

• Transmitted through body fluids: sexual contact, shared needles (IV drug users), and blood products.
• Also transmitted from mother to child during pregnancy, childbirth, or breastfeeding.

Natural History of HIV

• Typical course involves three phases:
  • Early, acute phase.
  • Middle, chronic phase.
  • Final, crisis phase.

Phases of HIV Infection

• Early Acute Phase:

  • Occurs 3-6 weeks post-exposure, resolves spontaneously in 2-4 weeks.
  • Symptoms include flu-like reactions, lymphadenopathy, decreased CD4 count.
  • Activation of CD8 T cells reduces viral load with CD4 count reaching 800 cells/µL.

• Middle Chronic Phase:

  • Lasts 2-15 years, often asymptomatic.
  • Characterized by persistent viral replication and gradual decline in CD4 count.
  • May experience generalized lymphadenopathy and minor opportunistic infections like thrush and herpes zoster.

• Final Crisis Phase:

  • Marked by a dramatic increase in viral load, long-lasting fever, weight loss, and diarrhea.
  • CD4 count drops below 500 cells, leading to AIDS-defining conditions.

AIDS-Defining Conditions

• Opportunistic infections include:
  • Protozoal: Cryptosporidiosis, Toxoplasmosis.
  • Fungal: Pneumocystis pneumonia, Candidiasis, Cryptococcosis.
  • Bacterial: Mycobacteriosis, Nocardiosis, Salmonella infections.
  • Viral: Cytomegalovirus infections, Herpes simplex virus, Varicella-zoster virus, Progressive multifocal leukoencephalopathy.

Variants and Exceptions

• Rapid Disease Progressors: Experience shortened chronic phase (2-3 years).
• Long-Term Non-Progressors: Remain asymptomatic for over 10 years with stable CD4 counts; mechanism not fully understood.
• Highly Exposed but Seronegative individuals: Maintain negative HIV status due to specific cytotoxic lymphocytes.
• Small Group Resistant to HIV: Possess mutations in cell surface receptors preventing HIV entry.

HIV Cell Tropism

• Viral glycoproteins gp120 and gp41 facilitate the infection:
  • gp120 binds to CD4 molecules and chemokine co-receptors (CCR5 and CXCR4).
  • CCR5 is expressed on macrophages, while CXCR4 is found on activated T cells.
• Subsequent to binding, gp41 fuses viral envelope with host cell membrane, allowing viral genome entry.

HIV Variants and Cell Types

• Lymphocyte tropic variants predominantly utilize CCR5 co-receptors, infecting macrophages and T cells.
• These are known as R5 viruses and require low levels of CD4 for infection.

This quiz covers key concepts related to AIDS defining conditions and the role of CD4 cells in immune response. It also addresses associated opportunistic infections such as fungal, protozoal, and helminthic infections. Test your knowledge on the key indicators and stages of AIDS.