Question
Hook worm
Answer
Hookworm infection is caused by Ancylostoma duodenale and Necator americanus, soil-transmitted intestinal nematodes, and a major cause of iron-deficiency anaemia in endemic tropical/subtropical regions.
Transmission: infective filariform (third-stage) larvae in warm, moist soil penetrate exposed human skin (typically bare feet) — a percutaneous route of infection (distinct from the faecal-oral egg-ingestion route of most other soil-transmitted helminths); A. duodenale can also be transmitted by oral ingestion of larvae.
Life cycle: larvae penetrating skin enter the bloodstream, undergo a pulmonary migration (similar to Ascaris) — reaching the lungs, ascending the bronchial tree, and being swallowed — before reaching the small intestine, where they attach to the mucosa via their buccal capsule (armed with cutting plates in Necator or teeth in Ancylostoma) and mature into adult worms.
Pathogenesis: 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 already malnourished populations; larval skin penetration can cause a local pruritic dermatitis (“ground itch”); pulmonary migration can cause mild respiratory symptoms.
Clinical features: iron-deficiency anaemia (pallor, fatigue), hypoalbuminaemia/protein loss in heavy infection, and, in children, potential growth/cognitive impairment from chronic anaemia and nutrient loss.
Laboratory diagnosis: stool microscopy for characteristic thin-shelled, oval, colourless eggs, typically containing a developing (4–8-cell stage) embryo in fresh stool.
Treatment: albendazole or mebendazole; iron supplementation to correct anaemia.
Prevention: sanitation (proper faecal disposal), wearing footwear in endemic areas, and periodic deworming programmes.