epidemiology, immunology and demographics

PART 1: HIV-1 VIROLOGY, PATHOGENESIS & THERAPY

1.1 Historical Context & Epidemiology

Emergence of HIV/AIDS:

1981: First clusters of unusual immune deficiencies reported in the US (Pneumocystis pneumonia, Kaposi's sarcoma).
1982: Term "Acquired Immunodeficiency Syndrome" (AIDS) coined.
1983-84: HIV-1 identified as causative agent by Luc Montagnier (France) and Robert Gallo (US).
1986: HIV-2 discovered in West Africa (less pathogenic, slower progression).

Origin:

Cross-species transmission from Simian Immunodeficiency Virus (SIV) in Central African chimpanzees (SIVcpz → HIV-1).
Estimated zoonotic jump in early 20th century (~1910-1930).
First confirmed human case: 1959 (Kinshasa, DRC).

Global Burden (2020s):

>40 million people living with HIV globally.
Sub-Saharan Africa bears ~70% of global burden.
~15 million on Antiretroviral Therapy (ART); major scale-up through PEPFAR and Global Fund.

1.2 HIV Structure & Life Cycle

Viral Structure:

Enveloped retrovirus (Lentivirus family).
Genome: Two identical single-stranded RNA strands.

Key Viral Proteins:

gp120 & gp41: Envelope glycoproteins for attachment/fusion.
p24: Capsid protein.
Reverse Transcriptase (RT), Integrase, Protease: Essential enzymes.

Life Cycle (Stepwise):

1. Attachment & Entry:

gp120 binds CD4 receptor on host cell (T-helper cells, macrophages, dendritic cells).
Conformational change exposes coreceptor binding site (CCR5 or CXCR4).
gp41 mediates fusion of viral envelope with cell membrane → entry.

2. Reverse Transcription:

RT converts viral ssRNA → dsDNA (proviral DNA).
Error-prone: High mutation rate (~1 error/2000 bases).

3. Integration:

Integrase enzyme inserts proviral DNA into host genome → provirus.
Establishes permanent, latent infection in long-lived cells.

4. Transcription & Translation:

Host machinery transcribes viral genes → viral mRNA → viral proteins.

5. Assembly & Budding:

New virions assemble at cell membrane, bud off, mature via protease cleavage.

1.3 Immunopathogenesis & Clinical Progression

Target Cells & Tropism:

Primary: CD4⁺ T-helper lymphocytes.
Also: Macrophages, monocytes, dendritic cells, microglia, gut epithelial cells.

Coreceptor Usage:

R5-tropic: Uses CCR5 (early infection, macrophage-tropic).
X4-tropic: Uses CXCR4 (later-stage, more cytopathic, T-cell-tropic).

Phases of Infection:

1. Acute Infection (Weeks 2-6):

Rapid viral replication, high viremia (10⁶–10⁷ copies/mL).
Flu-like illness (fever, rash, lymphadenopathy).
Massive depletion of gut-associated lymphoid tissue (GALT) CD4⁺ T-cells.

2. Clinical Latency (Chronic Phase):

Asymptomatic but active viral replication in lymphoid tissues.
Slow, steady decline in CD4⁺ count (50–100 cells/μL per year).
Persistent immune activation & inflammation.

3. AIDS (CD4⁺ <200 cells/μL):

Opportunistic infections (Pneumocystis jirovecii, TB, cryptococcal meningitis).
Malignancies (Kaposi's sarcoma, lymphoma).
Neurological disease (HIV encephalopathy).

Key Pathogenic Mechanisms:

CD4⁺ T-cell Depletion: Direct viral killing, apoptosis of bystander cells, immune exhaustion.
Chronic Immune Activation:
Due to microbial translocation from damaged gut barrier (endotoxemia).
Leads to hypergammaglobulinemia, T-cell senescence, fibrosis of lymphoid tissue.

Reservoir Formation:

Latent reservoirs in memory CD4⁺ T-cells, macrophages, CNS.
Sanctuary sites: Lymph nodes, CNS, testes (limited drug penetration).

1.4 Antiretroviral Therapy (ART)

Goals:

Maximal & durable suppression of viral load.
Restoration/preservation of immune function.
Reduction of HIV-related morbidity/mortality.
Prevention of transmission.

Classes of ART (c. 2020):

1. Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs/NtRTIs):

Mechanism: Chain terminators (lack 3′-OH).
Examples: Tenofovir (TDF/TAF), Emtricitabine (FTC), Abacavir (ABC), Zidovudine (AZT).

2. Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs):

Mechanism: Allosteric inhibition of RT.
Examples: Efavirenz, Rilpivirine, Doravirine.

3. Protease Inhibitors (PIs):

Mechanism: Inhibit viral protease → immature, non-infectious virions.
Examples: Darunavir, Atazanavir (boosted with Ritonavir/Cobicistat).

4. Integrase Strand Transfer Inhibitors (INSTIs):

Mechanism: Block integration of viral DNA.
Examples: Dolutegravir, Raltegravir, Bictegravir.

5. Entry/Attachment Inhibitors:

CCR5 Antagonist: Maraviroc.
Fusion Inhibitor: Enfuvirtide.
Post-attachment Inhibitor: Ibalizumab.

Current First-Line Regimens (WHO):

DTG-based: Dolutegravir + Tenofovir + Lamivudine (or Emtricitabine).
Advantages: High barrier to resistance, fewer side effects, once-daily dosing.

Treatment Challenges:

Adherence: Lifelong therapy, pill burden, side effects.
Drug Resistance: Due to high mutation rate, suboptimal adherence.

Long-term Toxicities:

Metabolic (lipodystrophy, dyslipidemia, insulin resistance).
Cardiovascular (increased MI/stroke risk).
Bone mineral density loss, renal impairment.

Therapeutic Strategies for Cure/Eradication:

"Shock and Kill": Latency-reversing agents (LRAs) like Histone Deacetylase Inhibitors, PKC agonists (Prostratin) to reactivate latent virus → kill by ART/immune system.
Immunotherapies: Broadly neutralizing antibodies (bNAbs), therapeutic vaccines, CAR-T cells.
Gene Editing: CCR5 knockout using CRISPR/Cas9 (inspired by CCR5-Δ32 mutation).

1.5 Prevention & Public Health

Biomedical Prevention:

PrEP (Pre-Exposure Prophylaxis): Tenofovir/Emtricitabine for high-risk individuals.
PEP (Post-Exposure Prophylaxis): 28-day ART course after potential exposure.
Treatment as Prevention (TasP)/U=U: Undetectable viral load = untransmittable.
PARTNER study (2016): Zero linked transmissions in serodifferent couples over 77,000 condomless sex acts.

Global Targets (UNAIDS 95-95-95 by 2030):

95% of PLHIV know their status.
95% of those diagnosed on ART.
95% of those on ART virally suppressed.

Key Populations:

Men who have sex with men (MSM), sex workers, people who inject drugs, prisoners, transgender individuals.

PART 2: ANTIVIRAL DRUG CHEMISTRY & MECHANISMS

2.1 Nucleoside Reverse Transcriptase Inhibitors (NRTIs) – Detailed Chemistry

Prototype: Zidovudine (AZT)

Chemical Structure: Thymidine analogue with azido group (-N₃) replacing 3′-OH on deoxyribose.

Activation: Intracellular phosphorylation by host kinases:

AZT → AZT-MP (thymidine kinase)
AZT-MP → AZT-DP (thymidylate kinase)
AZT-DP → AZT-TP (nucleoside diphosphate kinase)

Mechanism of Action:

AZT-TP competes with dTTP for incorporation by HIV RT.
Once incorporated, absence of 3′-OH prevents formation of phosphodiester bond with next nucleotide → chain termination.
Resistance: Mutations in RT (e.g., M41L, D67N, K70R, T215Y/F, K219Q) reduce binding/incorporation.

Other Key NRTIs:

Lamivudine (3TC): Cytidine analogue (–S– replacement in sugar ring). Low barrier to resistance (M184V mutation).
Tenofovir: Acyclic nucleoside phosphonate (phosphonate mimics phosphate). Prodrugs: TDF (disoproxil fumarate) & TAF (alanine phenyl ester).
Didanosine (ddI): Adenosine analogue. Activated to ddA-TP. Side effects: pancreatitis, peripheral neuropathy.

2.2 Anti-Herpes Drugs: Acyclovir & Mechanism

Acyclovir (ACV) – Prototype Anti-HSV Drug

Chemistry: Guanosine analogue with acyclic side chain (lacks 2′ & 3′ carbons of ribose).
Selective Activation (Key to Specificity):

1. First Phosphorylation: Viral Thymidine Kinase (TK) converts ACV → ACV-MP. This step occurs almost exclusively in HSV-infected cells.

2. Second Phosphorylation: Cellular GMP kinase converts ACV-MP → ACV-DP.

3. Third Phosphorylation: Cellular NDP kinase converts ACV-DP → ACV-TP.

Mechanism of Action:

ACV-TP competes with dGTP for viral DNA polymerase.
Incorporated into growing DNA chain → lacks 3′-OH → chain termination.
Viral DNA polymerase has higher affinity for ACV-TP than host polymerase.
Clinical Use: HSV-1/2, VZV. Prodrugs: Valacyclovir (better oral bioavailability).

2.3 Pharmacokinetics & Toxicity Considerations

NRTIs: Require intracellular activation. Toxicity often related to mitochondrial dysfunction (inhibit human DNA polymerase-γ) → lactic acidosis, hepatic steatosis, peripheral neuropathy.
Acyclovir: Renally excreted; risk of crystalluria/nephrotoxicity if hydrated inadequately.
Drug-Drug Interactions: Metabolized by hepatic enzymes (CYP450) or renal transporters; relevant for ART combinations.

PART 3: INTEGRATION WITH STI MANAGEMENT & ANAEMIA CONTEXT

3.1 HIV/STI Syndemic & Pharmacist Role

STI Co-infection Dynamics:

STIs (especially ulcerative: syphilis, herpes) increase HIV transmission risk 3-5x by disrupting mucosal barriers.
HIV increases STI acquisition risk and severity.

Pharmacist Interventions in STI Management (from STI PPT):

1. Testing & Triage:

Point-of-care tests (e.g., chlamydia/gonorrhoea NAAT, HIV rapid tests).
Signposting to sexual health clinics.

2. Treatment:

Supply prescribed antibiotics (e.g., doxycycline for chlamydia, ceftriaxone for gonorrhoea).
Directly provide treatments under PGDs (Patient Group Directions).

3. Partner Notification (PN):

Assist with patient-led PN, provide contact slips.
Digital PN via apps/texts.

4. Prevention:

Condom distribution, PrEP/PEP provision, HPV vaccination signposting.

5. Public Health Campaigns:

National Chlamydia Screening Programme (NCSP) for under-25s.
HPV vaccination (Gardasil-9) for boys/girls aged 12-13, MSM up to 45.

3.2 Anaemia in HIV & Chronic Disease

Causes of Anaemia in HIV:

1. Chronic Disease Anaemia (ACD):

Hepcidin-mediated iron sequestration.
Inflammatory cytokines suppress erythropoiesis.

2. Drug-Induced:

Zidovudine (AZT): Bone marrow suppression (macrocytic anaemia).
Other ART: Protease inhibitors can cause haemolytic anaemia.

3. Opportunistic Infections:

Parvovirus B19 (pure red cell aplasia), Mycobacterium avium complex.

4. Nutritional Deficiencies:

Iron, B12, folate deficiency due to malabsorption (HIV enteropathy).

Management (from Anaemia PPT):

Investigation: Full blood count, MCV, ferritin, B12, folate, reticulocyte count.
Iron Deficiency: Oral iron (65 mg elemental Fe daily), IV iron if malabsorption.
B12/Folate Deficiency: Hydroxocobalamin IM, oral folic acid.
ART Modification: Switch from AZT if causing severe anaemia.

3.3 Special Populations: Children & Adolescents with HIV

Mother-to-Child Transmission (MTCT):

Risk without intervention: 15–45%.
With full intervention (maternal ART, Caesarean, infant prophylaxis, no breastfeeding): <1%.
Infant Diagnosis: PCR for HIV DNA/RNA (maternal antibodies persist 18–24 months).

Paediatric ART:

Immediate ART for all infants <1 year regardless of CD4/viral load.
First-line: Abacavir + Lamivudine + Lopinavir/r (or Dolutegravir if >4 weeks old).
Challenges: Adherence, palatability, long-term toxicities (growth, neurodevelopment, cardiovascular).

Adolescents:

Barriers: Stigma, mental health, transition from paediatric to adult services.
Interventions: Cash transfers, free schooling, psychosocial support improve outcomes.

QUESTIONS

### Consolidated Core Notes: HIV-1, Antiviral Therapy & Integrative Management

#### 1. HIV-1 Virology, Pathogenesis & Clinical Course

* Structure: Enveloped retrovirus with ssRNA genome. Key proteins: gp120/gp41 (entry), Reverse Transcriptase (RT), Integrase, Protease.

* Life Cycle:

1. Attachment/Entry: Binds CD4 receptor + CCR5/CXCR4 co-receptor on T-cells/macrophages.

2. **Reverse Transcription:** RT converts viral RNA → dsDNA (**proviral DNA**). Error-prone → high mutation rate.

3. **Integration:** Integrase inserts proviral DNA into host genome → permanent latent reservoir.

4. Assembly/Release: New virions bud and are matured by Protease.

* Disease Progression:

* Acute: Flu-like illness, high viremia, gut CD4+ depletion.

* Chronic/Latent: Asymptomatic but active replication; slow CD4+ decline.

* AIDS (CD4+ <200 cells/μL): Opportunistic infections (e.g., PCP, TB), cancers.

#### 2. Antiretroviral Therapy (ART) - Drug Classes & Mechanisms

| :--- | :--- | :--- | :--- |

| NRTIs | Chain terminators (lack 3'-OH). Compete with natural nucleosides. | Zidovudine (AZT), Tenofovir (TDF/TAF), Lamivudine (3TC) | Activated intracellularly to triphosphate form. AZT can cause bone marrow suppression (anaemia). |

| Integrase Inhibitors (INSTIs) | Block integration of viral DNA into host genome. | Dolutegravir (DTG), Raltegravir | First-line (high barrier to resistance, good tolerability). |

| Entry Inhibitors | Block attachment (Maraviroc - CCR5 antagonist) or fusion (Enfuvirtide). | Maraviroc, Enfuvirtide | Used in salvage therapy or for multi-drug resistant virus. |

* **Modern First-Line Regimen:** Dolutegravir + Tenofovir + Lamivudine/Emtricitabine.

* U=U (Undetectable = Untransmittable): A person with a sustained undetectable viral load on ART cannot sexually transmit HIV.

#### 3. Key Antiviral Mechanisms (HIV & HSV)

* NRTI Mechanism (e.g., AZT):

1. Phosphorylated in cell to AZT-TP.

2. Competes with dTTP, incorporated by HIV RT into growing DNA chain.

3. Lacks 3'-OH → prevents addition of next nucleotide → chain termination.

* Acyclovir (ACV) Anti-HSV Mechanism:

1. **Selective Activation:** Viral Thymidine Kinase (TK) performs first phosphorylation (ACV→ACV-MP) only in infected cells.

2. Host kinases complete activation to ACV-TP.

3. ACV-TP (guanosine analogue) inhibits viral DNA polymerase, causing chain termination.

#### 4. Integration with STI Management & Anaemia

* STI/HIV Syndemic: STIs (especially ulcerative) increase HIV transmission risk. Pharmacists play key roles in testing, treatment (e.g., doxycycline for chlamydia), partner notification, and prevention (PrEP/PEP, condoms, HPV vaccination).

* Anaemia in HIV:

* **Causes:** Chronic disease (anaemia of inflammation), drug-induced (e.g., AZT), nutritional deficiencies, opportunistic infections.

* Management: Investigate (FBC, ferritin, B12/folate). Treat deficiency. May require ART switch (e.g., away from AZT).

#### 5. Prevention & Global Health

* **PrEP (Pre-Exposure Prophylaxis):** Tenofovir/Emtricitabine for high-risk individuals.

* PEP (Post-Exposure Prophylaxis): 28-day ART course, must start within 72 hours.

* Global Target (UNAIDS 95-95-95): By 2030: 95% know status, 95% on ART, 95% virally suppressed.

---

Part 1: Single Best Answer (SBA) Questions

1.

The modern first-line antiretroviral therapy (ART) regimen for HIV often includes Dolutegravir. To which class does Dolutegravir belong, and what is its primary mechanism?

a) NRTI; it acts as a chain terminator during reverse transcription.

b) Protease Inhibitor; it prevents the cleavage of viral polyproteins.

c) Integrase Strand Transfer Inhibitor (INSTI); it blocks the integration of viral DNA into the host genome.

d) NNRTI; it allosterically inhibits reverse transcriptase.

Answer:

c) Integrase Strand Transfer Inhibitor (INSTI); it blocks the integration of viral DNA into the host genome.

Dolutegravir is a preferred first-line INSTI due to its high barrier to resistance and good tolerability. It works by inhibiting the integrase enzyme, preventing the proviral DNA from being inserted into the host cell's DNA.

2.

A patient with HIV develops severe macrocytic anaemia after starting ART. Which antiretroviral drug is most likely responsible, and what is a key management step?

a) Tenofovir; switch to a different NRTI.

b) Efavirenz; reduce the dose.

c) Zidovudine (AZT); consider switching to an alternative NRTI like Abacavir or Tenofovir.

d) Darunavir; add folic acid supplementation.

Answer:

c) Zidovudine (AZT); consider switching to an alternative NRTI like Abacavir or Tenofovir.

AZT is well-known for causing bone marrow suppression, leading to macrocytic anaemia. A key management strategy is to switch to a less myelosuppressive NRTI (e.g., Abacavir or Tenofovir) while ensuring the new regimen maintains viral suppression.

3.

The high selectivity of Acyclovir for herpes simplex virus (HSV)-infected cells is primarily due to:

a) Its exclusive binding to viral envelope proteins.

b) Its initial activation by a host cell kinase found only in neurons.

c) Its preferential uptake by virus-infected cells via endocytosis.

d) Its first phosphorylation step being catalyzed by viral thymidine kinase (TK).

Answer:

d) Its first phosphorylation step being catalyzed by viral thymidine kinase (TK).

Acyclovir is a prodrug. The crucial first phosphorylation step is performed by the virus-encoded thymidine kinase, which has a high affinity for acyclovir. This enzyme is present in HSV-infected cells but not in uninfected human cells, providing excellent selectivity.

4.

According to the UNAIDS 95-95-95 targets for 2030, what does the final "95" represent?

a) 95% of people living with HIV (PLHIV) know their status.

b) 95% of PLHIV are receiving sustained antiretroviral therapy.

c) 95% of PLHIV on therapy are virally suppressed.

d) 95% reduction in new HIV infections.

Answer:

c) 95% of PLHIV on therapy are virally suppressed.

The 95-95-95 cascade is: 1) 95% of PLHIV know their status, 2) 95% of those diagnosed are on ART, and 3) 95% of those on ART are virally suppressed. Viral suppression is the ultimate goal for individual health and preventing transmission (U=U).

Part 2: Extended Matching Questions (EMQ)

Questions 5-7:

For each drug description, select the correct antiretroviral drug class.

Options:

A. Nucleoside Reverse Transcriptase Inhibitor (NRTI)

B. Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)

C. Integrase Strand Transfer Inhibitor (INSTI)

D. Protease Inhibitor (PI)

E. Entry Inhibitor

5.

Maraviroc, which blocks the CCR5 co-receptor on the host cell surface.

Answer:

E. Entry Inhibitor

Maraviroc is a CCR5 antagonist, a type of entry inhibitor. It prevents HIV from binding to and entering the host cell.

6.

Efavirenz, which binds to a hydrophobic pocket on reverse transcriptase, causing allosteric inhibition.

Answer:

B. Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)

Efavirenz is a classic NNRTI. It does not compete at the active site but binds nearby, distorting the enzyme's structure.

7.

Tenofovir disoproxil fumarate (TDF), an acyclic nucleoside phosphonate that requires intracellular phosphorylation to become an active chain terminator.

Answer:

A. Nucleoside Reverse Transcriptase Inhibitor (NRTI)

Tenofovir is an NRTI (specifically an NtRTI). It mimics a natural nucleotide and, once activated to tenofovir-diphosphate, causes chain termination during reverse transcription.

Part 3: Clinical Scenarios (OSCE/Patient Style)

Scenario 1: Counselling on U=U

A patient newly diagnosed with HIV is started on ART. After 6 months, their viral load is undetectable. Their partner, who is HIV-negative, is anxious about the risk of transmission.

How do you counsel them?

* State the Principle Clearly: "This is a very important and positive development. When someone with HIV is on effective treatment and has an undetectable viral load, it means the amount of virus in their blood is so low that it cannot be passed on to a sexual partner. This is known as Undetectable = Untransmittable, or U=U."

* Cite the Evidence: "This isn't just theory; it's based on major studies like the PARTNER study, which followed thousands of couples where one partner was HIV-positive and undetectable. They found zero linked transmissions through sex."

* Empower and Reassure: "This means you can have a normal, healthy sex life without fear of HIV transmission. It also shows how crucial it is for your partner to continue taking their medication regularly to stay undetectable."

Scenario 2: Managing a Potential Drug-Disease Interaction

A patient stable on Dolutegravir-based ART presents with a suspected STI and is prescribed doxycycline 100mg BD for 7 days.

Is there a significant interaction to be concerned about?

* Assessment: "There is a known interaction, but it is usually not clinically significant in this context."

* Mechanism: "Doxycycline can moderately reduce the absorption of Dolutegravir if taken at the exact same time, because doxycycline chelates divalent cations (like the metal ions in the dolutegravir tablet)."

* Practical Advice: "The simple advice is to separate the doses. The patient should take their doxycycline at least 2-3 hours before or 6 hours after their daily Dolutegravir dose. This avoids the interaction completely."

* Safety Net: "They should finish the full course of doxycycline. No change to their HIV medication is needed."

Part 4: Integration & Mechanism Application

Question 8: Linking Pathophysiology to Treatment

Why does the establishment of a latent viral reservoir in resting memory CD4+ T-cells pose the greatest challenge to curing HIV, and how does this relate to the mechanism of Integrase Inhibitors?

Answer:

* Challenge: The proviral DNA is integrated into the host cell's genome in these long-lived, resting cells. The virus is "hidden" and does not actively replicate, making it invisible to both the immune system and antiretroviral drugs that only target active replication (like NRTIs, NNRTIs, PIs).

* Relation to INSTIs: Integrase Inhibitors (e.g., Dolutegravir) block the integration step. However, they are only effective before integration occurs. Once a cell is latently infected (provirus integrated), INSTIs cannot eliminate it. This is why ART suppresses but does not eradicate HIV.

Question 9: Public Health & Pharmacy Role

A community pharmacist is running a sexual health promotion event. List three specific, evidence-based actions they could take to contribute to HIV prevention, aligning with the notes on STI management and prevention.

Answer:

1. PrEP Promotion & Signposting: Provide information on Pre-Exposure Prophylaxis (PrEP) and refer eligible, high-risk individuals (e.g., MSM, serodifferent couples) to local sexual health clinics for assessment and prescription.

2. Condom Distribution & STI Testing: Offer free condoms and promote opportunistic STI testing (e.g., chlamydia/gonorrhoea NAAT kits for under-25s, HIV rapid testing) to reduce STI incidence, which in turn lowers HIV transmission risk.

3. "U=U" Education & Stigma Reduction: Actively counsel that "Undetectable = Untransmittable," explaining that effective ART prevents sexual transmission. This combats stigma and encourages testing and treatment adherence.