Question
Classify nematodes, Enumerate intestinal nematodes. Add a note on life cycle, pathogenesis and lab diagnosis of Hookworm. (1+2+5)
Answer
Classification of nematodes: by habitat in the human host — intestinal nematodes (reside in the gut lumen) and tissue nematodes (reside in blood, lymphatics, subcutaneous tissue, or other organs, e.g., filarial worms).
Intestinal nematodes: Ascaris lumbricoides, hookworm (Ancylostoma duodenale, Necator americanus), Trichuris trichiura (whipworm), Enterobius vermicularis (pinworm), Strongyloides stercoralis.
Hookworm — life cycle, pathogenesis, and laboratory diagnosis
Life cycle: infective filariform (third-stage) larvae in warm, moist soil penetrate exposed human skin (typically bare feet); larvae enter the bloodstream, undergo pulmonary migration (reaching the lungs, ascending the bronchial tree/trachea, being swallowed), and reach the small intestine, where they attach to the mucosa via their buccal capsule (cutting plates in Necator, teeth in Ancylostoma) and mature into adult worms over several weeks; adult female worms produce eggs, passed in stool to continue the cycle in the environment.
Pathogenesis: larval skin penetration causes local pruritic dermatitis (“ground itch”); pulmonary migration can cause mild respiratory symptoms; adult worms attach to the intestinal mucosa and feed on blood, causing chronic occult intestinal blood loss — each worm causes a small but cumulatively significant daily blood loss, and heavy infection produces significant iron-deficiency anaemia, particularly problematic in malnourished populations; chronic heavy infection can also cause hypoalbuminaemia and, in children, impaired growth/cognitive development.
Laboratory diagnosis: stool microscopy for characteristic thin-shelled, oval, colourless (non-bile-stained) eggs, typically containing a developing 4–8-cell-stage embryo in fresh stool; stool concentration techniques improve sensitivity for light infections; larval culture (Harada-Mori technique) can be used to differentiate species when needed, since the two hookworm species’ eggs are morphologically indistinguishable.
Treatment: albendazole or mebendazole; iron supplementation to correct anaemia.
Prevention: sanitation, wearing footwear in endemic areas, periodic deworming programmes.