Question
Read the clinical history and answer the following questions: A 35 year old man presented to the medical OPD with a history of intractable diarrhea for the past one week. He gave past history of multiple exposures six months back. On clinical examination he was emaciated and oral thrush was present.
- (a) What is the provisional diagnosis. 1 mark(s)
- (b) Mention the different routes of transmission in this condition. 1 mark(s)
- (c) Explain the pathogenesis of the above clinical condition. 2 mark(s)
- (d) Describe briefly the laboratory investigations. 3 mark(s)
- (e) What is the confirmatory test. 1 mark(s)
- (f) Mention any four important opportunistic infections associated with this disease. 2 mark(s)
Answer
a) Provisional diagnosis: AIDS (Acquired Immunodeficiency Syndrome) — intractable chronic diarrhoea, wasting/emaciation, oral thrush (candidiasis), and a history of risk exposure 6 months earlier is classical of advanced HIV infection.
b) Routes of transmission: sexual contact (the predominant route), parenteral (blood/blood products, contaminated needles/injecting drug use, needle-stick injury), and vertical/perinatal transmission (mother-to-child — in utero, during delivery, or via breastfeeding).
c) Pathogenesis HIV (a retrovirus) primarily infects cells bearing the CD4 receptor (with a chemokine co-receptor, CCR5 or CXCR4) — chiefly CD4+ T-helper lymphocytes, but also macrophages and dendritic cells. Using reverse transcriptase, the viral RNA genome is converted to DNA, which integrates into the host cell genome (via integrase) and can remain latent or drive active viral replication, progressively destroying infected CD4+ cells. Over months to years, this causes a progressive decline in CD4+ T-cell count, crippling cell-mediated immunity. Once CD4 counts fall below critical thresholds, the patient becomes susceptible to characteristic opportunistic infections and malignancies, defining the transition from HIV infection to clinical AIDS.
d) Laboratory investigations
- Screening: ELISA for HIV antibody (and/or p24 antigen in 4th-generation combination assays) — high sensitivity, used as the initial screening test.
- Rapid tests: point-of-care immunochromatographic rapid antibody tests.
- CD4 count: flow cytometry to assess degree of immunosuppression and guide clinical staging/prophylaxis decisions.
- Viral load: quantitative HIV RNA PCR, used for monitoring disease progression and response to antiretroviral therapy.
- Other supportive findings: lymphopenia, and investigation for specific opportunistic infections as clinically indicated.
e) Confirmatory test: Western blot (detects antibody against specific individual HIV viral proteins, e.g., gp41, gp120/160, p24) — traditionally used to confirm a reactive screening ELISA; in many current programmes, a second, different ELISA/rapid test or a supplemental line immunoassay is used instead, per WHO/national testing algorithms, but Western blot remains the classically taught confirmatory reference method.
f) Four opportunistic infections associated with AIDS: Pneumocystis jirovecii pneumonia (PCP), oral/oesophageal candidiasis, cryptosporidiosis (a cause of the chronic diarrhoea in this patient), and cytomegalovirus (CMV) retinitis/disease (also toxoplasmosis, cryptococcal meningitis, and disseminated Mycobacterium avium complex are valid additional examples).