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 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 — 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 (cutting plates in Necator, 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; larval skin penetration causes a local pruritic dermatitis (“ground itch”); pulmonary migration can cause mild respiratory symptoms.
Clinical features: iron-deficiency anaemia (pallor, fatigue), hypoalbuminaemia 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 (non-bile-stained) eggs, typically containing a developing (4–8-cell stage) embryo in fresh stool.
Treatment: albendazole or mebendazole; iron supplementation to correct anaemia.
Prevention: sanitation, wearing footwear in endemic areas, periodic deworming programmes.