Trichuris trichiura, the whipworm, infects about 500 million persons throughout the world, particularly in humid tropical and subtropical environments. Infection is heaviest and most frequent in children. Infections are acquired by ingestion of eggs. The larvae hatch in the small intestine and mature in the large bowel to adult worms of about 4 cm in length (eFigures 35–33 and 35–34). The worms do not migrate through tissues.
Trichuris trichiura. Note copulatory bursa and single terminal spicule in male (above). Female at right. The worms inhabit the large intestine, with their narrow anterior ends sewn into the mucosa. (Reproduced, with permission, from Goldsmith R, Heyneman D [editors]. Tropical Medicine and Parasitology. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)
Life cycle of Trichuris trichiura. The unembryonated eggs are passed with the stool
. In the soil, the eggs develop into a 2-cell stage
, an advanced cleavage stage
, and then they embryonate
; eggs become infective in 15–30 days. After ingestion (soil-contaminated hands or food), the eggs hatch in the small intestine, and release larvae
that mature and establish themselves as adults in the colon
. The adult worms (approximately 4 cm in length) live in the cecum and ascending colon. The adult worms are fixed in that location, with the anterior portions threaded into the mucosa. The females begin to oviposit 60–70 days after infection. Female worms in the cecum shed between 3000 and 20,000 eggs per day. The life span of the adults is about 1 year. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.)
Most infected persons are asymptomatic. Heavy infections may be accompanied by abdominal cramps, tenesmus, diarrhea, distention, nausea, and vomiting. The Trichuris dysentery syndrome may develop, particularly in malnourished young children, with findings resembling inflammatory bowel disease including bloody diarrhea and rectal prolapse. Chronic infections in children can lead to iron deficiency anemia and growth retardation.
Trichuriasis is diagnosed by identification of characteristic eggs and sometimes adult worms in stools. Eosinophilia is common. Treatment is typically with albendazole (400 mg/day orally) or mebendazole (200 mg/day orally), for 1–3 days for light infections or 3–7 days for heavy infections, but cure rates are lower than for ascariasis or hookworm infection. An alternative is ivermectin (200 mcg/kg orally once daily for 3 days). Oxantel pamoate (one dose of 15–30 mg/kg) has shown good efficacy in clearing infections, and randomized trials showed albendazole plus oxantel pamoate (31% cure; 96% egg reduction) to be superior to mebendazole, and albendazole plus oxantel pamoate (69% cure; 99% egg reduction) and albendazole plus ivermectin (28% cure; 95% egg reduction) to be superior to albendazole plus mebendazole. Oxantel pamoate has low efficacy against Ascaris and hookworm infection.