HIV/AIDS

HIV / AIDS Study Guide for Medical Students

Definition

Human Immunodeficiency Virus (HIV) is a retrovirus that infects cells of the human immune system, primarily CD4+ T lymphocytes, macrophages, and dendritic cells, leading to progressive immunodeficiency. Acquired Immunodeficiency Syndrome (AIDS) is the most advanced clinical stage of HIV infection, defined by severe CD4+ T-cell depletion and/or the presence of specific AIDS-defining conditions (e.g., certain opportunistic infections and malignancies).

HIV exists as two main types: HIV-1, which is responsible for the global pandemic, and HIV-2, which is less transmissible and mainly endemic in West Africa. Both lead to progressive immune dysfunction if untreated.

Epidemiology

HIV remains a major global public health issue, particularly among adolescents and young adults and in key populations such as men who have sex with men (MSM), sex workers, and people who inject drugs. Persistent gaps in knowledge, stigma, and access to prevention and treatment continue to drive transmission, especially in younger populations. [5](https://pubmed.ncbi.nlm.nih.gov/41602051/) [10](https://europepmc.org/article/MED/41717609)

In many regions, studies of health-professional and student populations demonstrate variable knowledge and attitudes towards HIV and people with HIV (PWH), which can influence future quality of care. Improving provider knowledge and reducing stigma are identified as key components of HIV control efforts. [1](https://pubmed.ncbi.nlm.nih.gov/41832561/) [9](https://europepmc.org/article/MED/41764509)

Youth and young adults (15–24 years) have shown increasing rates of HIV and other sexually transmitted infections (STIs) such as syphilis and gonorrhea, highlighting the importance of integrated sexual health education and prevention services in this age group. [5](https://pubmed.ncbi.nlm.nih.gov/41602051/) [7](https://europepmc.org/article/PMC/PMC12989246)

Pathophysiology

1. Viral structure and entry

• HIV is an enveloped, single-stranded, positive-sense RNA retrovirus in the Lentivirus genus.
• Key structural proteins include gp120 and gp41 (envelope proteins), p24 (capsid), and enzymes reverse transcriptase, integrase, and protease.
• HIV targets cells expressing CD4 and co-receptors (CCR5 or CXCR4). Initial infection is typically CCR5-tropic (R5 virus), with potential later evolution to CXCR4-tropic strains associated with more rapid CD4 decline.

2. Replication cycle

• Attachment and fusion: gp120 binds CD4, then co-receptor (CCR5/CXCR4), causing conformational change and fusion of viral and cellular membranes via gp41.
• Reverse transcription: Viral reverse transcriptase converts viral RNA into double-stranded DNA, with high error rate leading to significant genetic variability and drug resistance potential.
• Integration: Viral DNA (provirus) is transported into the nucleus and integrated into host genome by integrase.
• Transcription/translation: Host machinery transcribes and translates viral genes, producing polyproteins and structural components.
• Assembly and budding: Immature virions assemble at the cell membrane and bud off; viral protease cleaves polyproteins to form mature infectious virions.

3. Immune system damage

• Progressive loss of CD4+ T cells via direct viral cytopathic effects, immune-mediated killing, and apoptosis.
• Destruction of gut-associated lymphoid tissue (GALT) early in infection, leading to microbial translocation and chronic immune activation.
• Chronic immune activation drives T-cell exhaustion, immunosenescence, and increased susceptibility to opportunistic infections and malignancies.
• Untreated, this leads to progressive CD4 decline and eventually AIDS-defining immunodeficiency.

Clinical Presentation

HIV infection has a spectrum of clinical stages: acute infection, chronic asymptomatic (clinical latency), symptomatic HIV infection, and AIDS. Presentations vary widely depending on stage and immune status.

Acute HIV Infection

Occurs typically 2–4 weeks after exposure and may be missed without high clinical suspicion.

• Symptoms: Mononucleosis-like illness: fever, sore throat, lymphadenopathy, rash (maculopapular), myalgias, arthralgias, headache. Sometimes oral ulcers or aseptic meningitis.
• Signs: Generalized lymphadenopathy, pharyngitis, hepatosplenomegaly; often non-specific.
• Key point: Viremia is very high, HIV antigen/viral load positive, antibody tests may be negative or indeterminate early on.

Chronic Asymptomatic (Clinical Latency)

• Patients may be clinically well for years with or without antiretroviral therapy (ART), depending on viral control and immune status.
• Persistent generalized lymphadenopathy may be present.
• Subclinical ongoing immune activation and CD4 decline occur if untreated.

Symptomatic HIV Infection (Pre-AIDS)

• Constitutional symptoms: weight loss, low-grade fever, night sweats, fatigue.
• Mucocutaneous: oral thrush, oral hairy leukoplakia, recurrent herpes simplex, herpes zoster, seborrheic dermatitis, molluscum contagiosum, warts.
• Hematologic: anemia, leukopenia, thrombocytopenia.
• Recurrent bacterial infections: sinusitis, pneumonia, skin infections.

AIDS (Advanced HIV Disease)

AIDS is defined by CD4+ T-cell count <200 cells/µL or the presence of one or more AIDS-defining conditions, irrespective of CD4 count. AIDS-defining illnesses involve opportunistic infections, certain malignancies, and specific HIV-related conditions.

• Opportunistic infections (examples):
  • Pneumocystis jirovecii pneumonia (PJP/Pneumocystis pneumonia): dyspnea, non-productive cough, hypoxia, diffuse bilateral interstitial infiltrates.
  • Mycobacterium avium complex (MAC): fever, weight loss, anemia, hepatosplenomegaly (often CD4 <50).
  • Toxoplasma gondii encephalitis: headache, focal neurologic deficits, seizures, multiple ring-enhancing brain lesions on imaging.
  • Cryptococcal meningitis: subacute headache, fever, meningismus, raised intracranial pressure.
  • Cytomegalovirus (CMV) retinitis: painless visual loss, floaters, retinal hemorrhages and exudates (“pizza pie” fundus).
  • Candida esophagitis: odynophagia, retrosternal pain.
  • Chronic herpes simplex or Varicella zoster reactivation: extensive or persistent lesions.
  • Recurrent severe bacterial infections: pneumonia, sepsis.
• AIDS-defining malignancies:
  • Kaposi sarcoma (HHV-8 associated; violaceous skin lesions, GI or pulmonary involvement).
  • High-grade non-Hodgkin lymphomas (especially diffuse large B-cell lymphoma, primary CNS lymphoma).
  • Invasive cervical carcinoma (HPV-associated).
• Other AIDS-defining conditions: HIV wasting syndrome, HIV-associated dementia, progressive multifocal leukoencephalopathy (JC virus).

Diagnosis

HIV diagnosis relies on a combination of serologic assays, virologic tests, and immunologic markers. Screening and confirmation algorithms may vary by country but follow similar principles.

1. Screening and Confirmatory Testing

• Fourth-generation HIV tests (preferred): Detect both HIV-1/2 antibodies and p24 antigen, allowing earlier detection than antibody-only tests.
• Initial screening: Laboratory-based or rapid fourth-generation combination immunoassays.
• Reactive screening test: Follow with supplemental antibody differentiation immunoassay to distinguish HIV-1 from HIV-2.
• Indeterminate or discordant results: Use HIV-1 RNA (NAAT) to resolve early infection versus false-positive serology.

2. Diagnosis of Acute HIV Infection

• Suspect in patients with compatible acute retroviral syndrome and recent high-risk exposure.
• HIV-1 RNA (viral load) is typically high; p24 antigen positive; antibodies may be negative or indeterminate.
• Definitive diagnosis: positive HIV-1 RNA in the appropriate clinical context with evolving serology.

3. Baseline Evaluation After HIV Diagnosis

• Confirmatory test: Repeat HIV-1/2 test to confirm diagnosis if needed.
• CD4+ T-cell count: Assesses immune status and risk of opportunistic infections.
• HIV viral load (HIV-1 RNA): Baseline level prior to ART initiation and for monitoring response.
• Resistance testing: Genotypic resistance assay, ideally before or soon after ART initiation.
• Routine labs: CBC, CMP (including renal and hepatic function), fasting lipids and glucose, urinalysis.
• Co-infection screening: Hepatitis B and C, syphilis, gonorrhea, chlamydia, TB (IGRA or TST), and other STIs as indicated. Young adults often have overlapping STIs, underscoring the need for comprehensive screening. [5](https://pubmed.ncbi.nlm.nih.gov/41602051/)
• Vaccination status: Evaluate and update (HBV, HPV, pneumococcal, influenza, etc.).

4. Monitoring

• CD4 count and viral load at baseline, 3 months after ART initiation or modification, then every 3–6 months once stable.
• More frequent monitoring in advanced disease, treatment failure, or adherence concerns.

Management

Management of HIV centers around early and sustained use of combination antiretroviral therapy (ART), prevention and treatment of opportunistic conditions, and comprehensive preventive care including sexual health and pre-exposure prophylaxis (PrEP) where appropriate. Provider preparedness for PrEP and HIV prevention care is critical, and targeted education for medical students and trainees improves efficacy of prevention strategies. [8](https://europepmc.org/article/PPR/PPR1157129) [9](https://europepmc.org/article/MED/41764509)

1. Principles of Antiretroviral Therapy (ART)

• Goals: Maximize and durable suppression of HIV viral load, restore and preserve immune function, reduce HIV-associated morbidity and mortality, and prevent transmission.
• General rule: ART is recommended for all persons with HIV, regardless of CD4 count, as soon as possible after diagnosis.
• Combination therapy: Typically 3 active drugs from at least 2 classes to prevent resistance (or 2 fully active drugs in certain integrase-based regimens, depending on guideline).

2. Antiretroviral Drug Classes (Overview)

• NRTIs (Nucleoside/Nucleotide Reverse Transcriptase Inhibitors): e.g., tenofovir disoproxil fumarate (TDF), tenofovir alafenamide (TAF), emtricitabine (FTC), lamivudine (3TC), abacavir (ABC). They are the backbone of most regimens; inhibit reverse transcriptase by chain termination.
• NNRTIs (Non-Nucleoside Reverse Transcriptase Inhibitors): e.g., efavirenz, nevirapine, rilpivirine, doravirine. Allosterically inhibit reverse transcriptase.
• Integrase Strand Transfer Inhibitors (INSTIs): e.g., dolutegravir, bictegravir, raltegravir, cabotegravir. Inhibit integration of viral DNA into host genome; highly effective and well tolerated.
• Protease Inhibitors (PIs): e.g., atazanavir, darunavir, typically boosted with ritonavir or cobicistat. Inhibit viral protease, preventing maturation of virions.
• Entry/Attachment Inhibitors: Maraviroc (CCR5 antagonist), enfuvirtide (fusion inhibitor), ibalizumab (post-attachment inhibitor), and others; usually reserved for treatment-experienced cases.

3. Initial ART Regimens (Conceptual)

Current guidelines favor once-daily, integrase inhibitor–based regimens using two NRTIs plus an INSTI, due to potent viral suppression, favorable side-effect profiles, and high barrier to resistance.

• Common regimen concepts include: tenofovir (TDF or TAF) + emtricitabine (FTC) or lamivudine (3TC) + dolutegravir/bictegravir, tailored to comorbidities, resistance profile, and drug–drug interactions.
• Abacavir-based regimens require HLA-B*57:01 testing because of hypersensitivity risk.

4. Management of Opportunistic Infections and Prophylaxis

• Pneumocystis jirovecii pneumonia (PJP) prophylaxis: Start TMP-SMX when CD4 <200 cells/µL or history of oropharyngeal candidiasis; discontinue when CD4 >200 for >3 months with virologic control.
• Toxoplasma gondii prophylaxis: TMP-SMX when CD4 <100 and Toxoplasma IgG positive.
• MAC prophylaxis: Azithromycin considered when CD4 <50 in settings where rapid ART initiation and viral suppression are not expected.
• Other prophylaxis: Tailored to local epidemiology and individual risk (e.g., TB preventive therapy if latent infection).
• Treatment: Standard antimicrobial regimens for each opportunistic infection, often longer duration and with ART optimization.
• Immune Reconstitution Inflammatory Syndrome (IRIS): In some patients starting ART with advanced disease, paradoxical worsening of known or unrecognized infections due to recovering immune responses; requires careful timing of ART, especially in TB and cryptococcal meningitis.

5. Prevention and Public Health Measures

• Pre-exposure prophylaxis (PrEP): Daily oral tenofovir-based regimens (e.g., TDF/FTC) or long-acting injectable cabotegravir in high-risk HIV-negative individuals. Provider knowledge and comfort in prescribing PrEP is crucial; educational gaps among medical students have been identified and should be addressed in curricula. [8](https://europepmc.org/article/PPR/PPR1157129)
• Post-exposure prophylaxis (PEP): Short course of combination ART after high-risk exposure (occupational or non-occupational), ideally within 72 hours.
• Prevention of mother-to-child transmission (PMTCT): Universal ART in pregnancy, optimized obstetric management, and neonatal prophylaxis drastically reduce perinatal transmission.
• Sexual health interventions: Condom promotion, STI screening and treatment, harm reduction for people who inject drugs, and structural interventions to reduce stigma and improve health-care access. [3](https://pubmed.ncbi.nlm.nih.gov/41717609/) [5](https://pubmed.ncbi.nlm.nih.gov/41602051/)

Psychosocial and Educational Aspects

HIV care is significantly influenced by healthcare providers’ knowledge, attitudes, and biases. Studies among medical and pharmacy students demonstrate that although knowledge can be high, misconceptions and stigma persist, potentially affecting future care of people with HIV. Targeted education improves attitudes, reduces stigma, and enhances preparedness for both treatment and prevention care such as PrEP. [1](https://pubmed.ncbi.nlm.nih.gov/41832561/) [8](https://europepmc.org/article/PPR/PPR1157129) [9](https://europepmc.org/article/MED/41764509)

Key Clinical Pearls

• Always consider acute HIV infection in patients with a mononucleosis-like illness and recent high-risk exposure, particularly when initial serology is negative but viral load is high.
• Fourth-generation assays detecting both antigen and antibody improve early diagnosis and should be the default screening test where available.
• Start ART as soon as possible after diagnosis in almost all patients; modern regimens are potent, well tolerated, and dramatically reduce transmission risk when viral suppression is achieved.
• CD4 count guides prophylaxis and risk stratification for opportunistic infections, but ART decisions are no longer CD4-dependent.
• Think broadly about co-infections (TB, HBV, HCV, syphilis, gonorrhea, chlamydia) in all patients with HIV, especially adolescents and young adults, given high rates of STI co-infection. [5](https://pubmed.ncbi.nlm.nih.gov/41602051/)
• Adherence counseling and psychosocial support are as important as regimen choice; address mental health, substance use, and stigma.
• PrEP and PEP are powerful prevention tools; medical students and trainees should be comfortable counseling, prescribing, and monitoring these interventions. [8](https://europepmc.org/article/PPR/PPR1157129)
• Stigma and provider attitudes directly impact patient outcomes; continual education is necessary to improve attitudes toward people living with HIV and enhance quality of care. [1](https://pubmed.ncbi.nlm.nih.gov/41832561/) [9](https://europepmc.org/article/MED/41764509)
• Family and social context influence preventive behaviors in young people, making family-centered and school-based interventions important for HIV and STI prevention. [3](https://pubmed.ncbi.nlm.nih.gov/41717609/) [7](https://europepmc.org/article/PMC/PMC12989246)

Summary

HIV/AIDS represents a chronic, manageable condition with effective ART, but it remains a significant public health challenge due to ongoing transmission, co-existing STIs, and persistent stigma. For medical students, a solid understanding of virology, clinical stages, diagnostic algorithms, and modern treatment strategies is critical, along with appreciation of the psychosocial, educational, and public health dimensions. Robust training in HIV care and prevention, including PrEP and comprehensive sexual health, is essential to meet the needs of diverse patient populations and to improve long-term outcomes for people living with or at risk for HIV. [1](https://pubmed.ncbi.nlm.nih.gov/41832561/) [5](https://pubmed.ncbi.nlm.nih.gov/41602051/) [8](https://europepmc.org/article/PPR/PPR1157129)