Hookworm anaemia — DTM&H MCQ

Correct answer: E — Necator americanus hookworm

The correct answer is E, Necator americanus hookworm. This child has severe microcytic iron deficiency anaemia (Hb 68 g/L) from chronic intestinal blood loss, and hookworm is the leading global cause of this pattern in endemic tropical settings. Thin shelled, oval, colourless eggs on stool microscopy are the classic morphology for hookworm species, distinguishing them from the thick shelled, mammillated eggs of Ascaris or the barrel shaped eggs of Trichuris. Barefoot walking is the key epidemiological clue, since filariform larvae of Necator americanus penetrate intact skin (commonly the feet) to establish infection, then migrate via the bloodstream and lungs to the small intestine. Adult worms attach to the mucosa and feed on blood continuously, and heavy or chronic burdens produce cumulative blood and iron loss sufficient to cause profound anaemia, exactly as described here. Why the other options are wrong: D. Schistosoma mansoni: infection is acquired by contact with freshwater containing cercariae, not by walking barefoot on soil, and its eggs are large with a characteristic lateral spine, not thin shelled ovals. B. Trichuris trichiura: produces barrel shaped eggs with bipolar plugs, not thin shelled ovals, and heavy whipworm infection causes anaemia mainly through colitis and rectal prolapse rather than the skin penetration route described. C. Ascaris lumbricoides: eggs are thick shelled and mammillated (or smooth if unfertilised), and Ascaris causes malabsorption and obstruction rather than clinically significant chronic blood loss anaemia. A. Enterobius vermicularis: causes perianal itching via eggs deposited around the anus (diagnosed by the sellotape test), not intestinal blood loss, and is not linked to barefoot soil contact. Key point: thin shelled oval eggs plus barefoot exposure equals percutaneous hookworm larval entry, the classic mechanism for tropical iron deficiency anaemia from chronic intestinal blood loss.

Reference: NICE CKS, Anaemia - Iron Deficiency (2024): lists hookworm infection as a cause of chronic gastrointestinal blood loss leading to iron deficiency anaemia, particularly relevant in patients from or visiting endemic tropical/subtropical areas. https://cks.nice.org.uk/topics/anaemia-iron-deficiency/