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Microbiology · Other RNA viruses

Human immunodeficiency virus !

  • Virus
  • Enveloped
  • Exam priority: high

A virus that slowly destroys the body's defences (CD4 cells). Untreated it leads to AIDS; with antiretrovirals people live long lives.

Updated 2026-11-01

Also called: HIV, HIV-1, HIV-2

At a glance

Shape
Spherical, with a cone-shaped capsid
Genome
Single-stranded, positive-sense RNA, diploid (two copies)
Envelope
Enveloped
Family
Retroviridae, genus Lentivirus
Size
About 80 to 120 nm

Morphology

  • Envelope with gp120 (binds CD4) and gp41 (fusion)
  • Cone-shaped p24 capsid holding two RNA copies, reverse transcriptase, integrase and protease
  • HIV-1 dominates worldwide; HIV-2, less virulent, is concentrated in West Africa

Transmission

  • Condomless sex (anal or vaginal)
  • Blood: shared needles, unscreened transfusions, sharps injuries
  • Mother to child in pregnancy, delivery or breastfeeding
  • Not spread by kissing, hugging, food or everyday objects

Reservoir: Humans; it arose from non-human primates in Africa

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Binding: gp120 attaches to CD4 and a co-receptor (CCR5 or CXCR4)
  2. Fusion: gp41 fuses the envelope with the membrane and the capsid enters
  3. Reverse transcription: reverse transcriptase copies RNA into double-stranded DNA
  4. Integration: integrase inserts the viral DNA (provirus) into the cell genome
  5. Replication: the cell transcribes the provirus and makes viral RNA and proteins
  6. Assembly and budding: new particles leave through the cell membrane
  7. Maturation: protease cuts the polyproteins and the virion becomes infectious

Virulence factors

  • Progressive loss of CD4 T cells and of cell-mediated immunity
  • Error-prone reverse transcriptase: high variability and drug resistance
  • The provirus integrated in latent cells forms a reservoir that blocks cure
  • Chronic immune activation and damage to the gut mucosa

Diseases it causes

  • HIV infection: acute, chronic asymptomatic and AIDS (advanced disease) HIV infection and AIDS →
  • Tuberculosis, the leading opportunistic infection and cause of death in people with HIV Tuberculosis →
  • Other opportunistic diseases: Pneumocystis pneumonia, cryptococcal meningitis, cerebral toxoplasmosis, Kaposi sarcoma and lymphomas

Clinical picture

  • Acute infection: mononucleosis-like illness with fever, sore throat, rash and lymph nodes, or no symptoms
  • Chronic asymptomatic phase for years with a gradual fall in CD4
  • Advanced disease: CD4 below 200 cells/µL or a WHO stage 3 or 4 event
  • AIDS: opportunistic infections, tuberculosis, defining cancers, wasting

Diagnosis

  • Rapid tests or a fourth-generation immunoassay (antibodies plus p24 antigen)
  • Confirmation with a testing algorithm before treatment starts
  • Viral load (RNA) for follow-up and CD4 count for staging
  • Under 18 months, virological testing (PCR), because maternal antibodies interfere
  • Window period: repeat the test after a recent exposure

Treatment

Combination antiretroviral therapy, started as soon as possible after diagnosis. The classes are: nucleoside/nucleotide reverse transcriptase inhibitors (tenofovir, lamivudine), non-nucleoside inhibitors (efavirenz), integrase inhibitors (dolutegravir), protease inhibitors (darunavir), entry or fusion inhibitors and capsid inhibitors. Resistance emerges when adherence fails; with an undetectable viral load there is no sexual transmission (undetectable = untransmittable).

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Condoms and regular testing for HIV and STIs
  • Pre-exposure prophylaxis (PrEP) with antiretrovirals for people at risk
  • Post-exposure prophylaxis (PEP), started as soon as possible after a risky exposure
  • Prevention of mother-to-child transmission with ART in pregnancy
  • Sterile equipment and harm-reduction programmes

Test yourself

Think of the answer, then tap the question to see it.

Which co-receptors does HIV use besides CD4?

CCR5 (macrophage-tropic strains, typical early on) and CXCR4 (T-cell-tropic strains, later).

What does a fourth-generation HIV test detect?

HIV antibodies and p24 antigen, which shortens the window period.

Which step of the life cycle does dolutegravir block?

Integration of viral DNA into the cell genome (integrase inhibitor).

Why is a six-month-old born to a mother with HIV tested by PCR, not antibodies?

Maternal antibodies cross the placenta and can persist up to 18 months.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: HIV and AIDS (World Health Organization (WHO), 2025); About HIV (CDC, 2025); Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions (CDC, 2024).

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