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Gut and tissue nematode infections acquired by ingestion 

Gut and tissue nematode infections acquired by ingestion

Gut and tissue nematode infections acquired by ingestion

David I. Grove



Ascaris suum—pig ascarid possibly adapting to humans in Japan.

Further reading—recent reviews added.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 28 April 2017


Ascaris lumbricoides (the giant roundworm) is widespread in the tropics and subtropics where sanitation is poor and the soil is contaminated with its eggs. Ingested eggs hatch in the small bowel, cycle through the bloodstream and lungs, then return to the small bowel and develop into adult worms 15 to 30 cm long. Most infections are asymptomatic, but there may be pulmonary infiltrates with eosinophilia, abdominal discomfort and—in children with heavy infections—intestinal obstruction. Infection is diagnosed by finding eggs in the faeces. Treatment is with pyrantel, mebedenazole, or albendazole.


This is caused by larvae of roundworms in the family Anisakidae, which are parasites of marine mammals. After ingestion of larvae in uncooked fish or squid, immature larvae burrow into the gastric or intestinal mucosa and may cause abdominal pain. Diagnosis is usually made at endoscopy, with treatment by endoscopic removal (if possible) of the larvae, although symptoms resolve spontaneously in most cases.


Intestinal capillariasis—caused by Paracapillaria philippinensis, this is acquired by ingestion of undercooked freshwater fish and may cause a severe diarrhoeal disease. Diagnosis is by finding eggs in the stool. Treatment is with mebendazole or albendazole. Prevention is by properly cooking fish.

Hepatic capillariasis—caused by Capillaria hepatica, a parasite of rats. Ingested eggs hatch and larvae pass to the liver and cause a syndrome similar to visceral larva migrans (see below). Diagnosis is made by identifying the parasite or eggs in a liver biopsy. Treatment is usually with thiabendazole or albendazole.


Enterobius vermicularis (the threadworm) is cosmopolitan. Ingested eggs develop directly into adult worms in the gut; fertilized female worms crawl out of the rectum at night and deposit eggs on the perianal skin. Most infections are asymptomatic, but pruritus ani may be troublesome at night. Diagnosis is made by finding eggs on clear adhesive tape applied to the perianal skin. Pyrantel, mebendazole, and albendazole are effective in combination with sanitary measures.


This is due to invasion by larvae of Toxocara canis and T. cati, acquired by ingestion of eggs from dog and cat stools. It occurs in two clinical forms—visceral and ocular larva migrans.

Visceral larva migrans—usually afflicts children; larvae migrate to the viscera and may be asymptomatic or cause protean manifestations including muscular pain, lassitude, anorexia, cough, urticarial rashes, hepatomegaly, and (occasionally) splenomegaly, lymphadenopathy and skin lesions, and (rarely) central nervous system involvement (convulsions). Eosinophilia is prominent. Definitive diagnosis is by finding larvae on biopsy, usually of the liver; a negative serological test for toxocara antibody rules out the diagnosis. Most patients recover spontaneously; there is no proven therapy.

Ocular larva migrans—more commonly seen in older children and due to granuloma formation around a larva in the retina. Diagnosis depends upon positive serology together with consistent fundoscopic features. There is no proven anthelmintic therapy.


This is acquired by ingestion of larvae of Trichinella spiralis in undercooked meat, usually pork. Adult worms in the small bowel produce larvae which seed the muscles and other tissues, where they develop. Most infections are asymptomatic, but heavy infections typically cause diarrhoea, followed by fever and myositis. Definitive diagnosis depends upon finding larvae in muscle biopsies, although this is usually unnecessary; serological tests become positive several weeks after infection. Treatment is symptomatic. Thorough cooking of pork is the best safeguard against infection.


Trichuris trichiura (whipworm) is most prevalent in the tropics and subtropics where sanitation is poor. Ingested eggs hatch in the small bowel and then develop within the gut into adult worms which become embedded in the large bowel mucosa. Very heavy infections may cause dysentery or rectal prolapse. Infection is diagnosed by finding eggs in the faeces. Treatment is with mebedenazole or albendazole.

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