Nematoda

Nematoda (round worm)

ASCARIS LUMBRICOIDES (ROUNDWORM) 

This pale yellow nematode is 20-35 cm long. Humans are infected by eating food contaminated with mature ova. Ascaris larvae hatch in the duodenum, migrate through the lungs, ascend the bronchial tree, are swallowed and mature in the small intestine.

This tissue migration can provoke both local and general hypersensitivity reactions with pneumonitis, eosinophilic granulomas, bronchial asthma and urticaria.

Normally, the adult worms are located in the small intestine. In unusual circumstances, such as fever, irritation due to drugs, anaesthesia, and bowel manipulation during surgery, the worms may migrate to ectopic sites where they may give rise to severe disease.

Clinical features 

Intestinal ascariasis causes symptoms ranging from occasional vague abdominal pain through to malnutrition. The large size of the adult worm and its tendency to aggregate and migrate can result in severe obstructive complications. In endemic areas ascariasis causes up to 35% of all intestinal obstructions, most commonly in the terminal ileum. Obstruction can be complicated further by intussusception, volvulus, haemorrhagic infarction and perforation. Other complications include blockage of the bile or pancreatic duct and obstruction of the appendix by adult worms.

Investigations  

The diagnosis is made microscopically by finding ova in the faeces. Adult worms are frequently expelled rectally or orally. Occasionally, the worms are demonstrated radiographically by a barium examination. There is eosinophilia. 

Management  

Mebendazole 100 mg 12-hourly for 3 days, albendazole 400 mg or piperazine 4 g as a single dose is effective for intestinal ascariasis. Patients should be warned that they may expel numerous whole, large worms. Obstruction due to ascariasis should be treated with nasogastric suction, piperazine and intravenous fluids.

Prevention 

Community chemotherapy programmes have been used to reduce Ascaris infection. The whole community can be treated every 3 months and over several years. Alternatively, schoolchildren can be targeted; treating them lowers the prevalence of ascariasis in the whole community.

Enterobiasis

Enterobiasis is a disease caused by Enterobius vermicularis infestation.

Children are more often involved than adults. It occurs in groups such as families living together, and in army camps.

This helminth is common throughout the world. It affects children especially. After the ova are swallowed, development takes place in the small intestine, but the adult worms are found chiefly in the colon. The male is approximately 5 mm long with a diameter of 0.1 to 0.2 mm. The female is approximately 13 mm long.

Clinical features:

The gravid female worm lays ova around the anus, causing intense itching, especially at night. The ova are often carried to the mouth on the fingers and so reinfection takes place. In females the genitalia may be involved. The adult worms may be seen moving onthe buttocks or in the stool. 

Investigations:

Ova are detected by applying the adhesive surface of cellophane tape to the perianal skin in the morning. This is then examined on a glass slide under the microscope. A perianal swab, moistened with saline, is an alternative method for diagnosis. 

Management: 

A single dose of mebendazole 100 mg, albendazole 400 mg or piperazine 4 g is given and may be repeated after 2 weeks to control auto-reinfection. Where infection constantly recurs in a family, each member should be treated as above. During this period all nightclothes and bed linen are laundered. Fingernails must be kept short and hands washed carefully before meals. Subsequent therapy is reserved for those family members who develop recurrent infection.