subject: Hookworm aetiology diagnosis and management [print this page] Hookworm aetiology diagnosis and management
This is infection of the gut with either Ancylostoma duodenaleor Necator americanus. Both grip the wall of themucosa with their mouth parts and take a small amount ofblood from the host each day. A relatively small numberof people develop disease related to hookworm infection.
Aetiology The worms are about 9 mm long. The female Ancylostomaproduces 30000 eggs per day and Necator 9000 eggs perday. Eggs must be passed into warm, moist soil for theovum to develop into the larval stage.Larvae of Necator grow in the lungs.Ancylostoma larvae can be ingested with food and developin the gut lumen without tissue migration.
Epidemiology Both species occur worldwide where temperature and soilconditions are suitable. Ancylostoma eggs are capableof resisting desiccation to some extent. Infection rates of360 80-90% are common in endemic rural areas. The use ofuntreated faeces as fertilizer on crops accounts for the high infection of farm workers.
Pathogenesis and pathology Each worm takes a small amount of blood from the host.Nutrients are removed by the parasite and the residuepasses into the gut, where it can be digested and absorbed.Iron deficiency anaemia occurs when iron losses exceed intake and iron stores are depleted. Anaemia may besevere, with haemoglobin levels of less than 5.0g/dL.Hypoalbuminaemia is usual at this stage, but malabsorptiondoes not occur.
Clinical features No symptoms are attributed to hookworm infection.Hookworm anaemia appears to cause few symptoms untiloedema due to hypoproteinaemia develops. Salt and waterretention exacerbates the oedema and causes some degreeof exertional dyspnoea. The findings are those of severeiron deficiency anaemia, with mucosal pallor and koilonychia.Some patients present with high-output congestivecardiac failure.
Diagnosis and investigation Diagnosis is confirmed by finding eggs in the faeces.Worm burden can be assessed from 24-hour faecal eggoutputs.Hypochromic microcytic anaemia is present. It isimportant to distinguish between iron deficiency andp-thalassaemia trait, which is common in the tropics.Eosinophil counts can be normal or increased, though theyare often markedly raised during the phase of migration.ManagementMebendazole (100 mg twice daily for 3 days) or albendazole(200 mg twice daily for 2 days) is effective. Bepheniumhydroxynaphthoate granules (5.0g) are given on an emptystomach. The cheapest treatment is tetrachlorethylenegiving 0.5mL/kg to a maximum single dose of5.0mL. Eradication of the worms is not the priority if anaemiais present. Packed cell transfusion may be needed aftergiving diuretics. Where there is heart failure, diuretics and cautious blood transfusion with packed cells are needed. Exchange transfusion is another way of correcting anaemia without risking the adverse effects of fluid overload. Later,iron stores will need replacing.
Prevention and control Safe disposal of faeces prevents transmission. Where nightsoil must be used to fertilize crops, prior chemical treatment kills ova. Wearing shoes or sandalsalso prevents infection. A diet with meat as a regular constituentwould prevent anaemia, but in the tropics and subtropicsthis is often beyond the means of many families andso vegetables with a high content of ferrous iron, e.g. soyabeans, should be introduced into the diet. Regular dewormingis increasingly used.
