What You Will Learn in This Article
- The complete timeline of HIV/AIDS discovery — dates, scientists, and institutions
- The Nobel Prize controversy between Montagnier and Robert Gallo
- Complete virology of HIV — structure, genome, classification
- The step-by-step pathogenesis of HIV — from entry to AIDS
- CD4 count thresholds and their clinical significance
- Opportunistic infections — which occur at what CD4 level
- Diagnosis of HIV — window period, tests, and their interpretation
- Antiretroviral therapy — classes, mechanisms, and combinations
- High-yield exam facts, mnemonics, and the most common exam traps
- 5 original practice MCQs to test yourself immediately
📖 Introduction: Why This Topic Matters in Exams
In 1981, young, previously healthy gay men in the United States began dying from unusual infections — Pneumocystis pneumonia and Kaposi’s sarcoma — diseases that had never been seen in immunocompetent people. The US Centers for Disease Control (CDC) noted a cluster of cases and described a new syndrome of immune deficiency. By 1982, it was named AIDS — Acquired Immunodeficiency Syndrome.
The race to identify the causative agent became one of the most celebrated — and controversial — scientific competitions of the 20th century. In 1983, two independent groups isolated the virus, and the ensuing dispute over credit culminated in a Nobel Prize in 2008. The year 1983 is one of the most tested dates in medical history MCQs — not just in microbiology, but across all of medicine.
This article gives you mastery over every examinable aspect: the history, the virus, the immunology, the diseases, and the treatments.
🔬 Section 1 — The History & Discovery of HIV: The Complete Timeline
Key Dates You Must Know
| Year | Event |
|---|---|
| 1959 | Oldest confirmed HIV-positive blood sample — from a man in Kinshasa, Democratic Republic of Congo (then Belgian Congo) |
| 1969 | HIV found retrospectively in a 15-year-old boy from St. Louis, Missouri who died of an AIDS-like illness |
| 1976 | HIV identified retrospectively in Norwegian sailor and his family who died of AIDS-like illness |
| 1981 | AIDS first described and reported by the CDC in the United States — 5 cases of Pneumocystis carinii pneumonia in gay men in Los Angeles |
| 1982 | Disease officially named AIDS (Acquired Immunodeficiency Syndrome) by the CDC |
| 1983 | HIV first isolated — by Luc Montagnier and Françoise Barré-Sinoussi at the Pasteur Institute, Paris; named LAV (Lymphadenopathy-Associated Virus) |
| 1983 | Robert Gallo (NIH, USA) also claims isolation of the virus — names it HTLV-III |
| 1984 | Margaret Heckler (US Health Secretary) announces Gallo discovered the “probable cause of AIDS” — leading to a long controversy |
| 1986 | International Committee on Taxonomy of Viruses (ICTV) renames the virus HIV (Human Immunodeficiency Virus) — resolving the LAV vs HTLV-III naming dispute |
| 1987 | Zidovudine (AZT) — first antiretroviral drug approved by the FDA |
| 1996 | Combination antiretroviral therapy (cART/HAART) introduced — transforms HIV from a death sentence to a manageable chronic illness |
| 2008 | Nobel Prize in Physiology or Medicine awarded to Luc Montagnier and Françoise Barré-Sinoussi for the discovery of HIV — Robert Gallo was controversially excluded |
The Nobel Prize Controversy
The 2008 Nobel Prize remains one of medicine’s most controversial. Robert Gallo’s group at the National Institutes of Health (NIH) published important work on HIV almost simultaneously with the Pasteur Institute. However, the Nobel Committee awarded the prize exclusively to the French scientists, recognising that Montagnier and Barré-Sinoussi were the first to isolate the virus from a patient.
Exam trap: MCQs may ask “Who discovered HIV?” or “Who received the Nobel Prize for HIV discovery?” — The answer in both cases is Luc Montagnier and Françoise Barré-Sinoussi, not Robert Gallo. The year of the Nobel Prize is 2008.
Why Is 1983 the Answer — Not 1981 or 1976?
- 1981 — AIDS was described as a syndrome (clinical entity), but the causative agent was unknown
- 1976 — Retrospective identification of HIV in stored samples from a Norwegian sailor; the virus was not discovered or isolated at the time
- 1983 — The virus was first isolated, cultured, and identified as the causative agent — this is the definition of “discovery”
- 1994 — This date corresponds to no major HIV milestone; it is a distractor
🔬 Section 2 — HIV Virology: Structure and Classification
Classification
- Family: Retroviridae
- Subfamily: Orthoretrovirinae
- Genus: Lentivirus
- Species: HIV-1 and HIV-2
HIV-1 vs HIV-2: HIV-1 is the predominant global strain — responsible for the worldwide pandemic. HIV-2 is found predominantly in West Africa, is less virulent, has a longer asymptomatic period, and lower transmission rates. Both cause AIDS but HIV-2 progresses more slowly.
Structure of HIV — The Complete Picture
HIV is a spherical enveloped virus, approximately 100–120 nm in diameter. From outside to inside:
Envelope:
- Lipid bilayer derived from the host cell membrane
- gp120 — outer envelope glycoprotein; binds to CD4 receptor on target cells; the primary attachment protein
- gp41 — transmembrane glycoprotein; mediates fusion of viral envelope with host cell membrane; the fusion protein
- Together gp120 and gp41 form a non-covalent heterodimer called gp160 (the precursor)
Matrix:
- p17 (matrix protein) — lies between the envelope and the capsid; helps in nuclear import
Capsid (Core):
- p24 (capsid protein) — forms the conical capsid; the target of the p24 antigen test used in HIV diagnosis
- p24 antigenemia occurs early in infection (before seroconversion) — important for early diagnosis
Contents of the Capsid:
- Two copies of single-stranded positive-sense RNA — the viral genome (diploid RNA)
- Reverse transcriptase (RT) — converts viral RNA → DNA; the target of NRTIs and NNRTIs
- Integrase — integrates viral DNA into host genome; the target of integrase inhibitors
- Protease — cleaves polyproteins into functional viral proteins; the target of protease inhibitors
- tRNA^Lys3 — the primer for reverse transcription
HIV Genome — The Nine Genes
The HIV genome contains 9 genes (compared to simple retroviruses which have only 3):
| Gene | Protein | Function |
|---|---|---|
| gag | p17, p24, p7, p6 | Structural proteins (matrix, capsid, nucleocapsid) |
| pol | Reverse transcriptase, Integrase, Protease | Enzymatic functions |
| env | gp120, gp41 | Envelope glycoproteins — attachment and fusion |
| tat | Tat | Transactivator — essential for viral replication |
| rev | Rev | Regulates mRNA export from nucleus |
| vif | Vif | Overcomes host APOBEC3G antiviral defence |
| vpr | Vpr | Facilitates nuclear import; G2 arrest |
| vpu (HIV-1 only) | Vpu | Enhances virion release; degrades CD4 in ER |
| nef | Nef | Downregulates CD4 and MHC-I; enhances infectivity |
Exam pearl: HIV has 9 genes — gag, pol, env (the three structural genes of all retroviruses) + 6 regulatory/accessory genes (tat, rev, vif, vpr, vpu, nef). This distinguishes HIV as a complex retrovirus from simple retroviruses.
🏥 Section 3 — Pathogenesis of HIV Infection
Step-by-Step Entry Mechanism
Step 1 — Attachment:
- HIV gp120 binds to CD4 receptor on target cells (CD4+ T lymphocytes, macrophages, dendritic cells)
- This binding causes conformational change in gp120
Step 2 — Co-receptor binding:
- The changed gp120 now binds to a co-receptor — either:
- CCR5 (C-C chemokine receptor 5) — used by M-tropic (macrophage-tropic) strains; dominant in early infection
- CXCR4 (C-X-C chemokine receptor 4) — used by T-tropic strains; dominant in late infection
- Co-receptor binding is essential for fusion
Clinical relevance: Individuals homozygous for CCR5 deletion (CCR5-Δ32) are highly resistant to HIV infection. This is why the “Berlin patient” (Timothy Ray Brown) was cured of HIV after receiving a bone marrow transplant from a CCR5-Δ32 donor — the first documented HIV cure.
Step 3 — Fusion:
- gp41 mediates fusion of viral envelope with host cell membrane
- Viral contents enter the cytoplasm
Step 4 — Reverse Transcription:
- Reverse transcriptase converts the viral ssRNA → dsDNA
- This is error-prone (no proofreading) → high mutation rate → rapid generation of drug-resistant variants
Step 5 — Integration:
- Viral dsDNA is transported to the nucleus
- Integrase integrates the viral DNA (now called a provirus) into the host chromosome
- The provirus remains latent or actively replicates
Step 6 — Transcription and Translation:
- Host RNA polymerase transcribes the provirus
- Tat protein dramatically increases transcription rate
- mRNAs are translated into viral polyproteins
Step 7 — Budding and Maturation:
- New virions bud from the cell membrane
- Protease cleaves the polyproteins during or after budding → mature, infectious virus
CD4 Count and Disease Progression
The CD4 T-lymphocyte count (normal: 500–1500 cells/μL) is the key prognostic marker:
| CD4 Count | Clinical Stage / Significance |
|---|---|
| >500 cells/μL | Normal or asymptomatic HIV infection |
| 200–500 cells/μL | Symptomatic HIV; minor opportunistic infections |
| <200 cells/μL | AIDS-defining threshold; major opportunistic infections begin |
| <100 cells/μL | Severe immunodeficiency; MAC, CMV retinitis |
| <50 cells/μL | Profound immunodeficiency; CMV disease, cerebral toxoplasmosis, PML |
🏥 Section 4 — Opportunistic Infections by CD4 Count
This is one of the most heavily tested tables in all of medicine:
| CD4 Count | Opportunistic Infection |
|---|---|
| <200 | Pneumocystis jirovecii pneumonia (PCP) — most common OI in AIDS; prophylaxis with TMP-SMX |
| <200 | Toxoplasma gondii — cerebral toxoplasmosis; ring-enhancing lesions on CT |
| <150 | Histoplasma capsulatum — disseminated histoplasmosis |
| <100 | Cryptococcus neoformans — cryptococcal meningitis; treat with amphotericin B + flucytosine |
| <100 | CMV retinitis — painless visual loss; “pizza pie” fundus |
| <50 | Mycobacterium avium complex (MAC) — disseminated; treat with azithromycin + ethambutol |
| <50 | Progressive Multifocal Leukoencephalopathy (PML) — JC virus; demyelinating disease |
| Any CD4 | Tuberculosis — most common OI in developing countries including India |
| Any CD4 | Kaposi’s Sarcoma — HHV-8; violaceous skin lesions |
| Any CD4 | Herpes Zoster — reactivation of VZV |
India-specific exam pearl: In India, Tuberculosis is the most common opportunistic infection in HIV-positive patients — not PCP (which is most common in Western countries). This geographic difference is tested in context-based MCQs.
🧪 Section 5 — Diagnosis of HIV
The Window Period
- Window period = time between HIV infection and the appearance of detectable markers (antibodies, antigen, or viral RNA)
- Varies by test used:
| Test | Window Period | What It Detects |
|---|---|---|
| NAT (Nucleic Acid Test / RNA PCR) | 10–33 days | HIV RNA — earliest detectable marker |
| p24 antigen test | 18–45 days | p24 capsid protein — antigen appears before antibodies |
| 4th Generation ELISA (Ag/Ab combo) | 18–45 days | Detects both p24 antigen AND HIV antibodies |
| 3rd Generation ELISA (Ab only) | 23–90 days | HIV antibodies (IgM + IgG) |
| Rapid antibody test | 23–90 days | HIV antibodies |
| Western Blot | 45–90 days | Confirms specific HIV protein bands |
Diagnostic Algorithm
- Screening: 4th generation ELISA (Ag/Ab combo) — high sensitivity
- If reactive: Repeat ELISA and/or Western Blot — high specificity for confirmation
- Western Blot positive criteria: Bands for gp120/gp160 + gp41 + p24 (at least 2 of these)
- Viral Load (HIV RNA PCR): Quantifies viral replication; guides treatment and monitors response
Exam trap: Western Blot is the confirmatory test. ELISA is the screening test. Never diagnose HIV on a single ELISA — always confirm with Western Blot (or a second ELISA of different design in resource-limited settings).
💊 Section 6 — Antiretroviral Therapy (ART)
Classes of Antiretroviral Drugs
| Class | Mechanism | Examples |
|---|---|---|
| NRTIs (Nucleoside/Nucleotide Reverse Transcriptase Inhibitors) | Competitive inhibitors of RT; lack 3′-OH for chain termination | Zidovudine (AZT), Tenofovir, Lamivudine, Emtricitabine, Abacavir, Stavudine |
| NNRTIs (Non-Nucleoside RT Inhibitors) | Non-competitive allosteric inhibitors of RT | Efavirenz, Nevirapine, Rilpivirine, Etravirine |
| PIs (Protease Inhibitors) | Block HIV protease → immature, non-infectious virions | Ritonavir, Lopinavir, Atazanavir, Darunavir |
| Integrase Inhibitors (INSTIs) | Block viral DNA integration into host genome | Raltegravir, Dolutegravir, Bictegravir |
| Fusion Inhibitors | Block gp41-mediated membrane fusion | Enfuvirtide (T-20) |
| CCR5 Antagonists | Block CCR5 co-receptor binding | Maraviroc |
Standard ART Regimen
Current guidelines (WHO, NACO) recommend:
- 2 NRTIs + 1 INSTI as the preferred first-line regimen
- Example: Tenofovir + Lamivudine + Dolutegravir (TLD) — the current preferred first-line in India and globally
- The goal: Suppress viral load to undetectable (<50 copies/mL)
“U = U” concept: Undetectable = Untransmittable — when viral load is suppressed to undetectable levels, HIV transmission risk is effectively zero. This is now a central message of HIV prevention.
Important Drug Side Effects (High-Yield)
| Drug | Key Side Effect |
|---|---|
| Zidovudine (AZT) | Bone marrow suppression → anaemia, neutropenia; myopathy |
| Tenofovir | Nephrotoxicity; Fanconi syndrome; bone mineral density loss |
| Efavirenz | CNS side effects (vivid dreams, dizziness); teratogenic (avoid in 1st trimester) |
| Nevirapine | Stevens-Johnson syndrome; hepatotoxicity |
| Abacavir | Hypersensitivity reaction — associated with HLA-B*5701 allele; screen before use |
| Lopinavir/Ritonavir | GI intolerance; dyslipidaemia; QT prolongation |
| Enfuvirtide | Injection site reactions (subcutaneous injection) |
🎯 High-Yield Exam Facts
These are the specific facts that appear repeatedly across NEET PG, USMLE, AIIMS and FMGE papers.
- 🔴 HIV was first discovered in 1983 — by Luc Montagnier and Françoise Barré-Sinoussi at the Pasteur Institute, Paris
- 🔴 Nobel Prize 2008 — awarded to Montagnier and Barré-Sinoussi; Gallo excluded controversially
- 🔴 AIDS defined by CD4 < 200 cells/μL OR presence of AIDS-defining illness regardless of CD4 count
- 🔴 HIV belongs to genus Lentivirus, family Retroviridae — a complex retrovirus with 9 genes
- 🔴 gp120 binds CD4; co-receptor is CCR5 (early) or CXCR4 (late) — co-receptor usage determines cell tropism
- 🔴 p24 antigen is the earliest detectable marker in acute HIV infection — before antibodies appear
- 🔴 Most common OI in AIDS globally = PCP (Pneumocystis jirovecii pneumonia) — prophylaxis: TMP-SMX when CD4 <200
- 🔴 Most common OI in AIDS in India = Tuberculosis — geographic distinction critical for context MCQs
- 🟠 First antiretroviral drug = Zidovudine (AZT) — approved 1987; NRTI; causes anaemia
- 🟠 CCR5-Δ32 homozygotes are resistant to HIV infection — basis for the Berlin patient cure
- 🟠 Western Blot = confirmatory test; ELISA = screening test — never diagnose on ELISA alone
- 🟠 Current preferred first-line ART in India = TLD — Tenofovir + Lamivudine + Dolutegravir
- 🟠 Abacavir hypersensitivity → test for HLA-B*5701 before prescribing — pharmacogenomics applied to HIV
- 🟡 HIV-2 predominates in West Africa — less virulent, slower progression, lower transmission
- 🟡 HIV genome is diploid — two identical copies of ssRNA in each virion
- 🟡 Reverse transcriptase has NO proofreading ability — explains high mutation rate and rapid resistance development
- 🟡 CMV retinitis occurs at CD4 <100 — “pizza pie” or “tomato ketchup” fundus; treat with ganciclovir
🧠 Mnemonics & Memory Tricks
Mnemonic 1: HIV Discovery — “In 1983, Montagnier Made Lentivirus Apparent” 1983 → Montagnier → Made → Lentivirus → Apparent (LAV = Lymphadenopathy-Associated Virus) Use it for: Locking in the year, scientist, and original name of HIV in one connected phrase
Mnemonic 2: HIV genes — “GAG POL ENV — TAT REV VIF VPR VPU NEF” The first three (gag, pol, env) are the structural genes shared by ALL retroviruses The last six (tat, rev, vif, vpr, vpu, nef) are the regulatory/accessory genes UNIQUE to complex retroviruses like HIV Memory hook: “GAG POL ENV = the basic template; TV VPN (tat, rev, vif, vpr, vpu, nef) = the advanced features” Use it for: Listing all 9 HIV genes without missing one
Mnemonic 3: Opportunistic infections by CD4 — “People Can’t Travel Hilly Country Mostly”
- PCP → CD4 <200
- Cerebral toxoplasmosis → CD4 <200
- TB → Any CD4 (in India — always)
- Histoplasmosis → CD4 <150
- Cryptococcal meningitis → CD4 <100
- MAC → CD4 <50 Use it for: Recalling OI thresholds in order from highest to lowest CD4
Mnemonic 4: ART drug classes — “Never Put In Freezing Cold Ice” NRTIs → PIs → INSTIs → Fusion inhibitors → CCR5 antagonists → (NNRTIs) Use it for: Recalling all major ART drug classes with their targets in sequence
Mnemonic 5: Western Blot positive criteria — “gp120 AND gp41 AND p24 = POSITIVE” Remember: “GPS confirms the address” — Gp120, Gp41 (two gps) + P24 = the three bands that confirm HIV on Western Blot Use it for: Answering “what constitutes a positive Western Blot result?”
⚠️ Common Mistakes Students Make
❌ Mistake: “AIDS was discovered in 1983 / HIV was described in 1981” ✅ Reality: These are two distinct events. AIDS (the syndrome) was first described/recognised in 1981 by the CDC in the USA. HIV (the causative virus) was first isolated and discovered in 1983 by Montagnier and Barré-Sinoussi. The MCQ asks specifically about the “causative agent” — that answer is 1983, not 1981. 📝 Exam trap: Option A in this MCQ was 1976 (retrospective Norwegian sailor case) — not the year of virus isolation. Option D was 1969 (retrospective St. Louis case). Neither constitutes “discovery” of the causative agent since the virus was identified retrospectively in stored samples, not actively isolated and characterised at those times.
❌ Mistake: “Robert Gallo discovered HIV and won the Nobel Prize” ✅ Reality: Robert Gallo made important contributions and his group simultaneously claimed discovery, but the Nobel Prize in 2008 was awarded exclusively to Luc Montagnier and Françoise Barré-Sinoussi of the Pasteur Institute. Gallo was not included. The Nobel Committee recognised the French team as the first to truly isolate the virus. 📝 Exam trap: “Who received the Nobel Prize for HIV discovery?” — Answer: Montagnier and Barré-Sinoussi (NOT Gallo). This name-based question appears in historical microbiology MCQs.
❌ Mistake: “CCR5 is the co-receptor for T-tropic strains; CXCR4 for M-tropic strains” ✅ Reality: This is exactly reversed. CCR5 is the co-receptor for M-tropic (macrophage-tropic) strains — which dominate in early infection. CXCR4 is the co-receptor for T-tropic strains — which emerge in late infection and predict faster progression to AIDS. CCR5-Δ32 deletion protects against infection precisely because M-tropic strains (which use CCR5) dominate in transmission. 📝 Exam trap: “Which co-receptor is used by the strain that predominates during sexual transmission?” — Answer: CCR5 (M-tropic strains are transmitted sexually and dominate early).
❌ Mistake: “ELISA alone confirms HIV infection” ✅ Reality: ELISA is a screening test with high sensitivity but lower specificity — false positives occur. A reactive ELISA must be confirmed by Western Blot (or immunofluorescence assay / line immunoassay / HIV-1/2 antibody differentiation immunoassay). A diagnosis of HIV should never be made on the basis of a single positive ELISA. 📝 Exam trap: “A patient has a positive ELISA for HIV. What is the next step?” — Answer: Confirmatory Western Blot. Not starting ART, not informing the patient of definitive diagnosis, not repeating ELISA alone.
❌ Mistake: “PCP is the most common OI in Indian HIV patients” ✅ Reality: In India (and other developing countries), Tuberculosis is the most common opportunistic infection in HIV-positive patients. PCP is the most common OI in developed/Western countries. This is because TB is endemic in India and can occur at any CD4 count, while PCP requires more profound immunosuppression (CD4 <200). Context-based MCQs specifically test this geographic variation. 📝 Exam trap: “In an HIV-positive patient from India, the most common opportunistic infection is?” — Answer: Tuberculosis. If the question says “globally” or in a Western context — PCP.
🔗 How This Topic Connects to Others
Mastering HIV connects to an enormous range of high-yield topics across multiple subjects:
- Immunology — CD4+ T cells — HIV targets CD4+ helper T cells; understanding their role in coordinating both humoral and cellular immunity explains why HIV causes susceptibility to such diverse infections
- Microbiology — Retroviruses — HIV as a retrovirus connects to the broader family: HTLV-1 (causes adult T-cell leukaemia), HTLV-2; reverse transcriptase as a shared enzyme; retroviral integration and latency
- Pharmacology — Antiretroviral drugs — NRTIs, NNRTIs, PIs, INSTIs are tested in mechanisms, side effects, and drug interactions across pharmacology papers; zidovudine in pregnancy (PMTCT) is a separate high-yield subtopic
- Opportunistic infections — PCP, toxoplasmosis, cryptococcal meningitis, CMV retinitis, MAC — each OI is independently examinable in medicine, microbiology, and ophthalmology papers
- Oncology — AIDS-defining malignancies — Kaposi’s sarcoma (HHV-8), Primary CNS lymphoma, Invasive cervical carcinoma — HIV-associated malignancies are tested in oncology and dermatology
- Obstetrics — Prevention of Mother-to-Child Transmission (PMTCT) — ART in pregnancy, mode of delivery, breastfeeding guidance — high-yield in OBG papers
❓ The MCQ That Started This — Fully Explained
Question: First time causative agent of AIDS was discovered in:
- A. 1976
- B. 1983
- C. 1994
- D. 1969
✅ Correct Answer: B. 1983
Why correct: In 1983, Dr. Luc Montagnier and Dr. Françoise Barré-Sinoussi at the Institut Pasteur in Paris, France, first isolated and characterised the causative agent of AIDS from a patient with lymphadenopathy. They named it LAV (Lymphadenopathy-Associated Virus). This was the first time the causative agent of AIDS was actively identified, isolated, grown in culture, and demonstrated to be the cause of the immune deficiency syndrome. They were awarded the Nobel Prize in Physiology or Medicine in 2008 for this discovery.
Why A is wrong: 1976 corresponds to retrospective identification of HIV in stored serum samples from a Norwegian sailor and his family who died of an AIDS-like illness. The virus was identified retrospectively — it was not discovered or isolated at that time. This does not constitute “first discovery” of the causative agent.
Why D is wrong: 1969 corresponds to the retrospective identification of HIV in stored tissue from a 15-year-old boy from St. Louis, Missouri who died of a mysterious immune deficiency illness. Again, this was retrospective analysis, not active discovery of the causative agent of AIDS.
Why C is wrong: 1994 does not correspond to any landmark HIV discovery. It falls within the era of growing understanding of HIV pathogenesis and early antiretroviral use, but no first discovery of significance occurred in that year. This is a pure distractor date.
📝 Test Your Understanding — 5 Practice MCQs
Q1. Which of the following is the EARLIEST detectable marker of acute HIV infection in a newly infected individual?
- A. HIV antibodies (IgG)
- B. Western Blot bands
- C. p24 antigen
- D. HIV RNA (by NAT/PCR)
✅ **D. HIV RNA (by NAT/PCR)** — HIV RNA becomes detectable by nucleic acid testing within 10–33 days of infection — the earliest of all HIV markers. p24 antigen appears at 18–45 days. HIV antibodies appear at 23–90 days. Western Blot bands appear latest (45–90 days). The sequence is: RNA → p24 antigen → IgM antibodies → IgG antibodies → Western Blot. This sequence defines the “window period” for each test — the period during which infection exists but the specific test is negative.
Q2. A 32-year-old HIV-positive man from Delhi has CD4 count of 180 cells/μL. He develops fever, cough, and night sweats. Chest X-ray shows upper lobe infiltrates with cavitation. What is the most likely opportunistic infection?
- A. Pneumocystis jirovecii pneumonia
- B. Pulmonary tuberculosis
- C. CMV pneumonitis
- D. Cryptococcal pneumonia
✅ **B. Pulmonary tuberculosis** — In an Indian patient with HIV, tuberculosis is the most common opportunistic infection at any CD4 count. Upper lobe infiltrates with cavitation is the classic radiological pattern of post-primary pulmonary TB. While PCP is common at CD4 <200, it presents with bilateral interstitial infiltrates (ground-glass pattern), not cavitating upper lobe disease. The clinical context (Indian patient + cavitation + night sweats) strongly points to TB. Remember: TB can occur at any CD4 level in India.
Q3. An HIV-positive patient with CD4 count of 60 cells/μL develops sudden painless visual loss in one eye. Fundoscopy reveals perivascular yellowish-white exudates with haemorrhages in a “pizza pie” distribution. What is the most likely diagnosis and treatment?
- A. Toxoplasma chorioretinitis — treat with pyrimethamine + sulfadiazine
- B. CMV retinitis — treat with ganciclovir
- C. Cryptococcal choroiditis — treat with amphotericin B
- D. HIV retinopathy — no treatment needed
✅ **B. CMV retinitis — treat with ganciclovir** — CMV retinitis occurs at CD4 <100 cells/μL and classically presents with painless visual loss and the “pizza pie” or “tomato ketchup” fundus appearance — yellowish-white necrotic areas with haemorrhages. Treatment is IV ganciclovir (or oral valganciclovir for maintenance). Toxoplasma retinochoroiditis gives a different pattern (white fluffy lesion with overlying vitreous haze — “headlight in fog”). HIV retinopathy (cotton wool spots alone) does not cause the pizza pie appearance and does not cause severe visual loss.
Q4. A patient is found to be HIV-positive on a 4th generation ELISA. Before starting treatment, a Western Blot is performed. Which combination of bands constitutes a positive Western Blot for HIV-1?
- A. p24 alone
- B. gp41 alone
- C. p24 + gp41 + gp120/gp160 (at least 2 of these 3)
- D. Any single band from gag, pol, or env regions
✅ **C. p24 + gp41 + gp120/gp160 (at least 2 of these 3)** — WHO and CDC criteria for a positive HIV Western Blot require the presence of at least 2 of the following bands: p24 (gag), gp41 (env transmembrane), and gp120/gp160 (env surface). A single band alone is indeterminate — not positive. An indeterminate result requires repeat testing in 4–6 weeks or supplementary testing with NAT. This specificity is why Western Blot serves as the gold-standard confirmatory test.
Q5. Which of the following antiretroviral drugs requires testing for HLA-B*5701 before initiation, and why?
- A. Tenofovir — to predict nephrotoxicity
- B. Efavirenz — to predict CNS side effects
- C. Abacavir — to prevent potentially fatal hypersensitivity reaction
- D. Zidovudine — to predict bone marrow suppression
✅ **C. Abacavir — to prevent potentially fatal hypersensitivity reaction** — Abacavir causes a severe, potentially life-threatening hypersensitivity reaction in patients carrying the **HLA-B*5701** allele (present in approximately 5–8% of Caucasians, less common in other populations). Symptoms include fever, rash, GI symptoms, and respiratory symptoms — progressing to multi-organ failure if the drug is not stopped and rechallenge is fatal. Screening for HLA-B*5701 before prescribing abacavir is mandated in current HIV treatment guidelines — a landmark example of pharmacogenomics applied to clinical practice.
📚 References & Further Reading
- Ananthnarayan & Paniker’s Textbook of Microbiology — Chapter on Human Immunodeficiency Virus: History, Classification, Structure, Pathogenesis
- Harrison’s Principles of Internal Medicine — Chapter on HIV Disease: AIDS and Related Disorders (comprehensive clinical reference)
- Katzung’s Basic & Clinical Pharmacology — Chapter on Antiviral Drugs: Antiretroviral Agents — Mechanisms, Resistance, Side Effects
- Robbins & Cotran Pathologic Basis of Disease — Chapter on Immunodeficiency Diseases: AIDS — Pathogenesis and Morphology
- NACO (National AIDS Control Organisation) Guidelines — ART Guidelines for HIV-Infected Adults and Adolescents in India (current first-line regimens)
🚀 Ready to Master Microbiology & Medicine?
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