T. trichiura is a common parasite and is found worldwide. Prevalence varies from 1% to 90%, being highest in poor communities with inadequate sanitation. Adult worms are most commonly found in the distal ileum and caecum, although in heavy infection no part of the colon is spared. The adult worm embeds its cephalic region into the intestinal mucosa, leaving the distal tail free within the lumen. Such invasion damages the intestinal mucosa and in heavy infection overt colonic and rectal ulceration may result, leading to significant blood and protein loss.
Most infections are asymptomatic and haematological or biochemical deficits do not occur provided nutritional intke is adequate. Heavy infection is associated with diarrhoea with blood and mucus, often associated with abdominal discomfort, tenesmus, anorexia and weight loss. Involvement of the appendix can cause appendicitis, and rectal prolapse has been reported in children.
Stool examination confirms the presence of typical barrelshaped eggs. Proctosigmoidoscopy may reveal adult worms firmly attached to the rectal mucosa.
Mebendazole 100 mg twice daily for 3 days or a single dose of pyrantel pamoate 10 mg kg-l are effective therapies.
Enterobius vermicularis (threadworm) infection
This parasite occurs worldwide but is more prevalent in temperate and cold climates. Children are most commonly infected, but it may affect whole families, inhabitants of residential institutions, and any group of people living in overcrowded circumstances. Adult worms reside largely in the colon, the female migrating to the anus to deposit embryonated eggs on the perianal and perineal areas. Superficial damage to the colonic mucosa occurs during heavy infection and secondary bacterial infection of these lesions may rarely result in submucosal abscesses.
Intense pruritus ani is usually the only symptom of threadworm infection. This is usually nocturnal and related to egg-laying in the perianal region by the female worms. Scratching results in dissemination of eggs and autoinfection. Infection has little significance while the parasite remains within the intestinal lumen, although on occasions migration occurs to the peritoneum and the viscera may be involved.
Diagnosis is best achieved by applying a piece of clear adhesive tape to the perianal region; this tape may then be examined microscopically for the presence of adherent eggs. Adult worms may be observed leaving the anus bythe child’s parents.
A single dose of mebendazole 100 mg followed by a second dose 2 weeks later is usually effective. Alternatives include pyrantel pamoate or piperazine. Family members should also be treated.