(a) (i) Enumerate different species of Aspergillus and the infections caused by them. Give the laboratory diagnosis of a case of…

(a)(i) Aspergillus species, infections and diagnosis of pulmonary aspergillosis

Species and diseases:

• A. fumigatus (commonest): allergic bronchopulmonary aspergillosis, aspergilloma (fungal ball in old tubercular cavities), chronic pulmonary and invasive aspergillosis in neutropenic or transplant patients.
• A. flavus: sinusitis, keratitis (common in India), invasive disease, aflatoxin (hepatocellular carcinoma).
• A. niger: otomycosis, aspergilloma.
• A. terreus: invasive disease, intrinsically resistant to amphotericin B.
• A. nidulans: chronic granulomatous disease, mycetoma. Laboratory diagnosis (sputum, bronchoalveolar lavage, biopsy):
• KOH or calcofluor-white mount: narrow (3–6 μm), septate hyphae with dichotomous acute-angle branching.
• Culture on Sabouraud dextrose agar (without cycloheximide): rapid growth, colony colour and lactophenol cotton blue mount for species.
• Histopathology with GMS or PAS showing tissue invasion (proof of invasive disease).
• Galactomannan antigen in serum or BAL, β-D-glucan, PCR.
• Serology: Aspergillus-specific IgG for aspergilloma and chronic disease, total IgE and specific IgE with eosinophilia for ABPA.
• HRCT: halo sign, air-crescent sign, fungal ball.

(a)(ii) Dysentery: bacterial versus amoebic and diagnosis of amoebic dysentery

Dysentery is inflammation of the colon with frequent passage of small stools containing blood and mucus, with abdominal cramps and tenesmus. Bacterial (bacillary, mainly Shigella, also EIEC, Campylobacter, Salmonella) versus amoebic (Entamoeba histolytica):

• Onset: acute with high fever and toxaemia, versus gradual with little fever.
• Stools: frequent, small, scanty faecal matter, bright blood and mucus, odourless, alkaline, versus fewer, larger, faecal, dark blood mixed with mucus, offensive, acidic.
• Microscopy: many pus cells and macrophages, RBCs in rouleaux, no trophozoites, versus few pus cells, clumped RBCs, Charcot–Leyden crystals and motile trophozoites with ingested RBCs.
• Pathology: diffuse superficial ulceration of the rectum and sigmoid, versus discrete flask-shaped ulcers in the caecum and ascending colon with normal intervening mucosa. Laboratory diagnosis of amoebic dysentery: fresh warm stool saline and iodine mounts for haematophagous trophozoites (12–60 μm, directional motility) and quadrinucleate cysts, repeated on three samples, formol-ether concentration, stool antigen ELISA specific for E. histolytica (distinguishes from E. dispar), PCR, culture (Boeck–Drbohlav medium) where available, serology (useful in liver abscess), and sigmoidoscopy with scrapings or biopsy.

(b)(i) Drowning and its types

Drowning is the process of respiratory impairment from submersion or immersion in liquid, the commonest cause of death being asphyxia from fluid aspiration. Types:

• Wet (typical) drowning (80–90%): water aspirated into the lungs. Fresh water is absorbed into blood causing haemodilution, haemolysis, hyperkalaemia and ventricular fibrillation within minutes. Salt water (hypertonic) draws fluid into alveoli causing pulmonary oedema, haemoconcentration and slower death.
• Dry drowning (10–15%): reflex laryngospasm prevents water entry, death by asphyxia, little water in lungs.
• Immersion syndrome (hydrocution): sudden cardiac arrest from vagal inhibition when cold water hits the face, larynx or epigastrium, or on entering water after alcohol.
• Secondary (delayed) drowning: death hours to days after rescue from pulmonary oedema, ARDS, pneumonia or electrolyte disturbance.
• Shallow-water drowning: in a small amount of water when the victim is drunk, epileptic, infant or unconscious. Autopsy pointers: fine, persistent froth at mouth and nostrils, emphysema aquosum, water and silt in the airways and stomach, diatoms in bone marrow and organs, washerwoman hands.

(b)(ii) Hyoid bone and its fractures

The hyoid is a U-shaped bone at C3 level, with a body, two greater cornua and two lesser cornua, suspended by muscles and ligaments (stylohyoid ligament to lesser cornu, thyrohyoid membrane to the upper border). The greater cornua fuse with the body in middle age, so fracture is commoner in older people. Fractures (usually of the greater cornu at the junction of its middle and posterior thirds):

• Inward compression fracture: in throttling (manual strangulation), the fingers press the cornua inward, fragment displaced inward, with haemorrhage at the site. A strong indicator of homicide.
• Antero-posterior compression fracture: from a direct blow or ligature pressure, fragments displaced outward.
• Avulsion (traction) fracture: in hanging, the thyrohyoid membrane pulls the cornu, displaced outward, less common than in throttling.
• Direct trauma fractures of the body from blows or falls. Antemortem fracture shows haemorrhage and vital reaction at the site, distinguishing it from postmortem or autopsy artefact.

(c)(i) Mechanism of action of metformin

• Main action: reduces hepatic glucose output by inhibiting gluconeogenesis. It inhibits mitochondrial complex I (raising AMP), activating AMP-activated protein kinase (AMPK), and inhibits mitochondrial glycerophosphate dehydrogenase and adenylate cyclase signalling of glucagon.
• Increases insulin sensitivity and glucose uptake in muscle (GLUT4 translocation) and fatty acid oxidation.
• Reduces intestinal glucose absorption and increases GLP-1, with weight neutrality or mild loss.
• It does not release insulin, so it does not cause hypoglycaemia alone. Main risk: lactic acidosis in renal failure (avoid if eGFR below 30), hypoxia or liver disease, and B12 deficiency with long use.

(c)(ii) Thiazides: indications and adverse effects

Thiazides (hydrochlorothiazide, chlorthalidone, indapamide) block the Na⁺–Cl⁻ symporter in the distal convoluted tubule. Indications: hypertension (first-line), mild oedema of heart failure, liver or renal disease, idiopathic hypercalciuria with calcium stones, nephrogenic diabetes insipidus, and osteoporosis risk reduction. Adverse effects: hypokalaemia and metabolic alkalosis, hyponatraemia, hypomagnesaemia, hypercalcaemia, hyperuricaemia (gout), hyperglycaemia, hyperlipidaemia, erectile dysfunction, photosensitivity and sulfonamide hypersensitivity. They are less effective when GFR is low (except metolazone).