Microbiology · MU Sofia

95. Family Retroviridae – HIV-1 and HIV-2

Covers the general features of HIV-1 and HIV-2 within the Retroviridae family, then their structure and genome, including a table of envelope, capsid and enzyme components. It goes on to the replication cycle, the stages of pathogenesis and clinical features from acute infection through latency to AIDS with a list of opportunistic illnesses. It closes with a comparison table of HIV-1 and HIV-2, diagnostic tests, combination treatment and prevention measures.

Inside: 10 sections · 5 labelled pictures · 2 tables · 15 flashcards · 4 min

Topic 95 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 10 sections, about 370 words (4 min of reading), with 15 flashcards.

In this note

  1. Family Retroviridae – HIV-1 and HIV-2
  2. I. General Characteristics
  3. II. Structure and Genome
  4. III. Replication Cycle (Key to Pathogenesis)
  5. IV. Pathogenesis
  6. V. Clinical Features
  7. VI. Differences Between HIV-1 and HIV-2
  8. VII. Diagnosis
  9. VIII. Treatment
  10. IX. Prevention

I. General Characteristics

  • Family: Retroviridae | Genus: Lentivirus
  • Human Immunodeficiency Virus (HIV) includes:
  • HIV-1: Most widespread globally; more virulent
  • HIV-2: Less transmissible, slower progression to AIDS; mostly in West Africa
  • Enveloped, spherical virus, ~100–120 nm in size
  • Genome: 2 copies of (+)ssRNA, diploid, reverse transcribed into DNA
  • Contains enzyme reverse transcriptase, integrase, protease
  • Transmission via:
  • Sexual contact
  • Blood transfusion/needle sharing
  • Vertical (mother-to-child): transplacental, perinatal, breastfeeding

III. Replication Cycle (Key to Pathogenesis)

  1. 1. Attachment: gp120 binds to CD4 on T-helper cells, macrophages, dendritic cells
  • Requires co-receptor: CCR5 (early), CXCR4 (late-stage)
  1. 2. Fusion: via gp41 → viral entry into cell
  2. 3. Reverse Transcription: RNA → cDNA via reverse transcriptase
  3. 4. Integration: cDNA integrated into host genome by integrase
  4. 5. Latency or active replication (depending on immune state)
  5. 6. Budding and maturation: new virions released, matured by protease

IV. Pathogenesis

  • HIV targets and destroys CD4+ T cells → gradual immune system collapse
  • Early stage: high viremia, transient drop in CD4+ cells, flu-like illness
  • Clinical latency: low viremia, stable CD4 count, virus persists in lymphoid tissue
  • AIDS: CD4 < 200 cells/μL or presence of AIDS-defining illnesses (e.g., PCP, Kaposi sarcoma)

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