Infectious Disease Pathology
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Direct answer
Infectious disease pathology for FMGE is anchored in the Indian burden: tuberculosis with caseating granulomas under the National Tuberculosis Elimination Programme; leprosy across its tuberculoid-to-lepromatous spectrum with multidrug therapy; typhoid with Peyer patch ulcers; dengue, malaria, kala-azar, filariasis and hydatid disease; and HIV. Each disease carries a hallmark cell, pigment, granuloma or programme tag that examiners convert into single-best-answer questions, so buzzword fluency pays more here than anywhere else.
What you must remember
- Tuberculosis: primary Ghon complex of subpleural focus with hilar node; post-primary apical cavitary disease; caseating granulomas with Langhans giant cells; India carries the world's highest burden under the national elimination programme with Nikshay notification.
- Leprosy: Mycobacterium leprae, uncultivable, infecting Schwann cells; tuberculoid paucibacillary disease with few anaesthetic hypopigmented plaques and strong immunity against lepromatous multibacillary disease with nodules, lion facies and globi; type 1 reversal and type 2 erythema nodosum leprosum reactions; paucibacillary and multibacillary multidrug therapy per the national programme; ulnar and great auricular nerves thicken.
- Bacterial classics: diphtheria's grey pseudomembrane with bull neck and Albert-stain metachromatic granules; tetanus risus sardonicus; cholera rice-water stools; typhoid with step-ladder fever, rose spots, Peyer patch ulcers and gallbladder carriage; syphilis with chancre, condylomata lata and gumma; scrub typhus eschar in the Indian monsoon.
- Viral: dengue with plasma leakage, thrombocytopenia and shock syndrome from Aedes; Japanese encephalitis from Culex; rabies Negri bodies; measles Koplik spots; infectious mononucleosis with atypical lymphocytes and positive Monospot; HIV with CD4 decline — oral candidiasis, Pneumocystis below 200 cells, toxoplasmosis and cryptococcosis below 100.- Fungal: mucormycosis in diabetic ketoacidosis with black necrotic turbinates; angioinvasive aspergillosis with haemoptysis; mycetoma (Madura foot) with sinus grains, a rural Indian classic.
- Parasitic: falciparum malaria causing cerebral disease and blackwater while vivax relapses; kala-azar with LD bodies in macrophages, splenomegaly, pancytopenia, rK39 diagnosis and liposomal amphotericin in endemic eastern India; amoebic flask-shaped ulcers with anchovy-paste liver abscess; hydatid daughter cysts with anaphylaxis on spillage; cysticercosis brain seizures; filarial lymphoedema under mass drug administration; hookworm iron deficiency.
Common confusion
Tuberculoid versus lepromatous leprosy anchors cell-mediated immunity against anergy — and the reactions differ: type 1 nerve-function worsening against type 2 systemic erythema nodosum leprosum. Amoebic abscess is single, anchovy-paste and metronidazole-responsive; pyogenic abscess is often multiple with a biliary source. Only falciparum routinely causes cerebral malaria.
Exam-focused takeaway
FMGE quotes the histological clue — Langhans cell, LD body, Negri body, flask ulcer, scolex in a brain cyst — and expects disease plus first-line drug under the relevant programme. Dengue warning signs, malaria species-phenotype pairing, leprosy classification and multidrug therapy, and HIV CD4 thresholds are fixed favourites; programme tags appear as public-health one-liners.
Frequently asked questions
What is the histological hallmark of tuberculosis?
The caseating granuloma — amorphous central necrosis ringed by epithelioid macrophages, Langhans giant cells and lymphocytes — a type IV hypersensitivity response.
How do tuberculoid and lepromatous leprosy differ?
Tuberculoid disease shows strong immunity with few anaesthetic plaques and scarce bacilli; lepromatous disease shows anergy with infiltrations, globi and systemic involvement needing longer multidrug therapy with clofazimine.
Which malaria species causes cerebral disease?
Plasmodium falciparum through sequestration in cerebral microvessels, also causing severe anaemia and blackwater; vivax relapses from liver hypnozoites.
What are dengue warning signs?
Abdominal pain, persistent vomiting, mucosal bleeding, lethargy, tender hepatomegaly and rising haematocrit with falling platelets — impending shock needing careful isotonic fluids; avoid aspirin.
How does kala-azar present?
Prolonged fever with massive splenomegaly, pancytopenia and hypergammaglobulinaemia; LD bodies and rK39 testing support diagnosis, with liposomal amphotericin first-line in India's programme.
Which parasite causes seizures in an Indian child?
Neurocysticercosis from Taenia solium larvae, with a ring lesion and eccentric scolex on imaging; albendazole with corticosteroids and antiepileptics is standard care.