## Correct Answer: C. Enterobius vermicularis Enterobius vermicularis (pinworm) is the most common helminthic infection in children worldwide and in India, particularly in school-age populations. The clinical presentation is pathognomonic: intense **perianal itching at night** occurs because gravid females migrate to the perianal region after dark to deposit eggs, causing intense pruritus that disrupts sleep. This nocturnal symptom is the discriminating clinical feature. Microscopic examination reveals **barrel-shaped eggs with flattened sides** (characteristic morphology), typically found on perianal skin scrapings or tape swabs rather than stool examination. The infection spreads via fecal-oral route, with high transmission in crowded settings like schools and daycare centers common in Indian urban and semi-urban areas. Diagnosis is confirmed by the "Scotch tape test" (cellophane tape pressed to perianal skin in early morning). Unlike other helminths, E. vermicularis causes minimal intestinal pathology but significant morbidity due to pruritus, sleep disturbance, and behavioral problems in children. Treatment with albendazole or mebendazole (single dose, repeated after 2 weeks) is highly effective and is the standard DOC in India per IAP guidelines. ## Why the other options are wrong **A. Trichuris trichiura** — Trichuris causes **chronic diarrhea and dysentery** with rectal prolapse in heavy infections, not isolated nocturnal perianal itching. Eggs are **barrel-shaped with polar plugs** (distinctive from Enterobius) and are found in stool, not perianal scrapings. Trichuriasis is more common in rural areas with poor sanitation and presents with lower abdominal pain and bloody stools—a completely different clinical picture from the question stem. **B. Hymenolepis nana** — Hymenolepis nana is a tapeworm causing **abdominal pain, diarrhea, and malabsorption**, not perianal itching. Eggs are **round with a polar filament** and are detected in stool samples, not perianal scrapings. H. nana infection is rare in Indian children compared to E. vermicularis and does not present with the characteristic nocturnal pruritus that defines pinworm disease. **D. Ancylostoma duodenale** — Ancylostoma causes **iron-deficiency anemia, protein malnutrition, and ground itch** (pruritus at the site of larval penetration on feet/legs), not perianal itching. Hookworm eggs are **oval with thin shells** and are found in stool. Ancylostomiasis presents with systemic symptoms (anemia, fatigue) and cutaneous manifestations at entry sites, not the isolated nocturnal perianal symptom described. ## High-Yield Facts - **Nocturnal perianal itching** is the pathognomonic presentation of Enterobius vermicularis; caused by gravid females migrating to deposit eggs at night. - **Scotch tape test** (cellophane tape pressed to perianal skin in early morning) is the gold standard diagnostic method; stool examination often misses pinworms. - **Barrel-shaped eggs with flattened sides** are the characteristic morphology of E. vermicularis on microscopy. - **Albendazole 400 mg single dose, repeated after 2 weeks** is the standard DOC in India; treats the patient and prevents reinfection. - **Most common helminthic infection in Indian school children**; spreads via fecal-oral route in crowded settings; entire family often requires treatment. - **No intestinal pathology** despite high prevalence; morbidity is behavioral (sleep disturbance, irritability) rather than nutritional or hemodynamic. ## Mnemonics **PINWORM = Night Itching** **P**erianal itching at **NIGHT** → **E. vermicularis**. Remember: Pinworms = Perianal + Night. All other helminths cause GI symptoms, not perianal itch. **Scotch Tape = Pinworm Diagnosis** When you see **perianal itching + child**, think **Scotch tape test**. Stool exam will miss it; tape swab from perianal skin in early morning catches the eggs. ## NBE Trap NBE pairs "perianal itching" with hookworm (Ancylostoma) to trap students who confuse ground itch (larval entry site pruritus on feet) with perianal pruritus (gravid female migration). The nocturnal timing is the key discriminator that points to pinworm, not hookworm. ## Clinical Pearl In Indian pediatric practice, a child presenting with sleep disturbance, irritability, and nocturnal perianal itching should trigger immediate suspicion for pinworm infection—it is far more common than other helminthiases in urban/semi-urban school-age children. A single-dose albendazole with repeat dosing after 2 weeks, combined with hygiene counseling (short nails, frequent hand-washing), resolves the infection in >95% of cases and prevents family transmission. _Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 46 (Nematodes); Park's Textbook of Preventive and Social Medicine Ch. 7 (Communicable Diseases)_
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