subject: Ascariasis aetiology and management [print this page] Ascariasis aetiology and management Ascariasis aetiology and management
Aetiology The adult female worm measures up to 400mm long by6mm wide at its thickest. The male is up to300mm long by 2-4 mm. They live for about 1 year. Bothare a greyish-white colour. The female lays up to 200000eggs per day. The worms do not attach themselves to thegut mucosa but maintain their position by actively movingagainst the flow of intestinal contents. The eggs survive wellin warm moist soil but are killed by heating to 50 C.Distribution and incidenceAscariasis is common in the tropics and subtropics, and upto 90% of people may be infected. Poor or absent sanitationand frequent faecal contamination of the environmentwith vast numbers of Ascaris eggs lead to a high frequencyof infection, often with large worm loads in children.
Transmission and epidemiology Eggs are ingested in food or water or from fingers, and thelarvae are released in the small intestine. They enter themucosa and then blood vessels to reach the lungs, wherethey leave blood vessels and enter air spaces. Here theyundergo two further moults and then ascend the bronchialtree to the pharynx. They migrate down the oesophagusand through the stomach to reach the small intestine.An excess of infections is found in a small proportionof the population, the reasons for which are uncertain.However, among this group there is evidence of undernutrition,perhaps because of the effect of the worm bulkcreating a sense of satiety, with consequent reduction infood intake.
Pathology No intestinal mucosal lesions are attributable to the adultworms. Pulmonary infiltrates with eosinophils are foundduring the larval migratory phase of the lifecycle, but thisrarely has a clinical correlate.
Clinical features Symptoms due to the migrating phase of ascariasis are veryuncommon. Pulmonary infiltrates on X-ray, eosinophiliaand restrictive pulmonary function defects can occur. Thiscan be seen when humans are infected with the pig ascaris,Ascaris suum.There are also few symptoms attributable to establishedinfection. Worms may be vomited, or passed with thestools, or may even emerge from a nostril. Bolus obstructionof the small intestine occurs, particularly in childrenwith very heavy infections. A mass of matted worms in asegment of gut can cause intestinal obstruction, volvulusand infarction. Occasionally an adult worm will migrate.into the common bile duct, causing pain, obstructive jaundiceand ascending cholangitis, or into the pancreatic ductto cause pancreatitis. Ascarids can also migrate throughintestinal suture lines to cause leakage from an anastomosis.Ascaris egg granulomas are occasionally found in theperitoneal cavity, presumably related to ectopic developmentof an adult female.
Diagnosis Diagnosis is made by finding eggs in faecal samples. Thecomplications of ascariasis are usually diagnosed on surgicalexploration or endoscopic examination. Eosinophilia isuncommon, apart from at the stage of tissue migration.
Management Mebendazole (100 mg twice daily for 3 days) or albendazole(400 mg as a single dose) is effective. Both drugs arerelatively expensive.Piperazine hydrate elixir (750 mg of hydrate per 5mL) iseffective. The dose depends on age and weight. Where amixed infection of ascaris and hookworm is being treatedwith piperazine and tetrachlorethylene (TCE) for hookworm,it is usual to treat the ascaris first, as TCE may stimulateascaris migration into biliary or pancreatic ducts.
Prevention and control The use of latrines would prevent infection. Regularadministration of drugs, e.g. albendazole, in affected communitiesis being used. Faecal contamination of the environmentand the use of human faeces as fertilizer on cropsencourage transmission. Before use as fertilizer, faeces canbe treated with sodium nitrate or calcium superphosphateto kill the eggs of gut parasites. Education of the communityabout the control efforts, and their active cooperation,are essential to the success of control programmes.
