Correct Answer: C. Trichuris trichiura
Trichuris trichiura (whipworm) is the causative agent identified by the pathognomonic barrel-shaped (lemon-shaped) eggs in stool examination. The clinical presentation of bloody and mucus-filled diarrhea, tenesmus, abdominal pain, and rectal prolapse is classic for trichuriasis, particularly in heavy infections common in India's tropical regions. The whip-like morphology of the adult worm (thin anterior, thick posterior) allows it to embed deeply in the colonic mucosa, causing chronic inflammation, mucosal ulceration, and bleeding. Tenesmus (painful straining) and rectal prolapse occur due to the irritative effect of worms in the rectosigmoid region and increased intraluminal pressure from diarrhea. Heavy infections (>400 worms) are associated with protein-losing enteropathy and iron-deficiency anemia. The barrel-shaped eggs are diagnostic—they are 50–55 μm × 22–24 μm with characteristic bipolar plugs (mucoid polar prominences) that distinguish them from other helminth eggs. Trichuriasis is endemic in rural India, particularly in areas with poor sanitation, and is transmitted via contaminated food and water.
Why the other options are wrong
A. Ancylostoma duodenale — Ancylostoma duodenale (hookworm) causes iron-deficiency anemia and protein malnutrition but does NOT produce bloody diarrhea with tenesmus or rectal prolapse. Its eggs are oval and embryonated (not barrel-shaped), and the worm localizes to the small intestine, not the colon. Hookworm causes occult blood loss, not visible bloody diarrhea. B. Ascaris lumbricoides — Ascaris lumbricoides produces large, oval, thick-shelled eggs (60–75 μm × 40–50 μm), NOT barrel-shaped eggs. While Ascaris can cause abdominal distension and pain, it does not typically cause bloody mucoid diarrhea or tenesmus. Ascaris-related complications (obstruction, intussusception) are mechanical, not inflammatory. D. Giardia lamblia — Giardia lamblia is a protozoan that causes watery, fatty, foul-smelling diarrhea (steatorrhea), NOT bloody mucoid diarrhea with tenesmus. Giardia cysts are pear-shaped or oval, not barrel-shaped. Rectal prolapse is not a feature of giardiasis. Giardia affects the small intestine (duodenum/jejunum), not the colon.
High-Yield Facts
- Barrel-shaped (lemon-shaped) eggs with bipolar plugs are pathognomonic for Trichuris trichiura and distinguish it from all other helminths.
- Tenesmus and rectal prolapse in a child with bloody diarrhea in India should immediately raise suspicion for trichuriasis, especially in endemic rural areas.
- Heavy trichuriasis (>400 worms) causes protein-losing enteropathy, iron-deficiency anemia, and growth retardation in children—a major public health problem in India.
- Trichuris embeds in the colonic mucosa (not the small intestine like Ascaris or hookworm), causing mucosal ulceration and visible blood in stool.
- Albendazole 400 mg single dose is the DOC for trichuriasis in India; mebendazole is an alternative (both are broad-spectrum antihelmintics).
Mnemonics
WHIP = Trichuris Whipworm = White eggs with Heavy Inflammation of Prostate/rectum. Whip shape (thin anterior, thick posterior) embeds in colon → bloody diarrhea + tenesmus + rectal prolapse. Barrel ≠ Ball Barrel-shaped = Trichuris (bipolar plugs). Ball-shaped = Ascaris (round). Oval = Hookworm. Use egg morphology to differentiate the 'Big 3' helminths in India.
NBE Trap
NBE pairs "bloody diarrhea + abdominal pain" with Ascaris or hookworm to trap students who focus on GI symptoms alone and ignore the pathognomonic barrel-shaped eggs and tenesmus/rectal prolapse that are specific to colonic trichuriasis.
Clinical Pearl
In rural India, a child presenting with bloody diarrhea, tenesmus, and rectal prolapse should be examined for barrel-shaped eggs in stool—trichuriasis is endemic in areas with poor sanitation and is easily missed if the clinician focuses only on symptoms rather than the diagnostic egg morphology. A single dose of albendazole is curative and prevents complications like anemia and growth stunting.
_Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 46 (Helminths); Park's Textbook of Preventive and Social Medicine Ch. 8 (Communicable Diseases)_