Correct Answer: B. Enterobius vermicularis
Enterobius vermicularis (pinworm) is the most common helminthic infection in children worldwide and particularly prevalent in India. The clinical presentation is pathognomonic: nocturnal perianal itching is the hallmark symptom, caused by gravid females migrating out of the anus at night to deposit eggs on the perianal skin. This triggers intense itching, especially in children, leading to sleep disturbance and behavioral problems. The adhesive tape test (Scotch tape test) is the gold standard diagnostic method—when applied to the perianal area in the morning, it captures eggs and motile worms, which are then visualized under the microscope. The worms are small (8–13 mm), white, and thread-like, often visible to the naked eye (as the mother observed). Transmission is fecal-oral, via contaminated fomites, making it highly contagious in schools and households. Unlike other helminths, E. vermicularis does not require soil incubation and spreads rapidly in crowded settings. Treatment with albendazole or mebendazole (single dose, repeated after 2 weeks) is highly effective. The infection is self-limiting but causes significant morbidity due to pruritus and secondary bacterial infection from scratching.
Why the other options are wrong
A. Hymenolepis nana — Hymenolepis nana (dwarf tapeworm) causes intestinal infection but does NOT present with nocturnal perianal itching. It is asymptomatic in most cases or causes mild abdominal discomfort and diarrhea. Diagnosis is by stool examination (proglottids/eggs), not adhesive tape test. While H. nana is common in India, the clinical presentation and diagnostic method are entirely different from the case described. C. Ancylostoma duodenale — Ancylostoma duodenale (hookworm) is endemic in India but causes iron-deficiency anemia, protein malnutrition, and ground itch (at site of larval penetration), NOT nocturnal perianal itching. Diagnosis is by stool examination showing characteristic hookworm eggs. The clinical presentation and diagnostic approach are completely different; adhesive tape test is not used for hookworm detection. D. Trichuris trichiura — Trichuris trichiura (whipworm) causes chronic diarrhea, dysentery, and rectal prolapse in heavy infections, but NOT the characteristic nocturnal perianal itching seen with pinworms. Diagnosis is by stool examination showing barrel-shaped eggs with mucoid plugs. While common in India, the clinical symptomatology and diagnostic method differ significantly; adhesive tape test is not the standard diagnostic tool.
High-Yield Facts
- Nocturnal perianal itching is the pathognomonic presentation of Enterobius vermicularis infection in children.
- Adhesive tape test (Scotch tape applied to perianal area in early morning) is the gold standard diagnostic method for pinworm; stool examination is often negative.
- Fecal-oral transmission via contaminated fomites (bedding, clothing, toys) makes E. vermicularis highly contagious in schools and households.
- Single-dose albendazole or mebendazole (10–15 mg/kg) is the treatment of choice; repeat dose after 2 weeks to eliminate newly matured worms.
- Gravid females migrate out at night to deposit eggs on perianal skin, causing intense itching and sleep disturbance in affected children.
- Self-limiting infection but causes significant morbidity; secondary bacterial infection from scratching is common in Indian children.
Mnemonics
PINWORM = Night Itch Perianal itching at Night = Enterobius vermicularis. Remember: mothers see white worms in stool/perianal area at night; tape test catches them. Tape Test = Pinworm Only E. vermicularis is reliably diagnosed by adhesive tape test (not stool exam). All other helminths → stool examination. Tape test = Think Pinworm first.
NBE Trap
NBE pairs "nocturnal perianal itching" with "worm seen by mother" to lure students into choosing tapeworms (H. nana) or other intestinal helminths. The key discriminator is the adhesive tape test—only pinworm eggs are reliably captured this way; other helminths require stool examination.
Clinical Pearl
In Indian schools and daycare centers, pinworm outbreaks are common and often missed because mothers report "white worms in stool" but stool examination is negative—the key is to perform an adhesive tape test on the child in the early morning before bathing. Treating the entire household (including asymptomatic family members) is essential to prevent reinfection, a practice often overlooked in resource-limited Indian settings.
_Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 46 (Helminths); Harrison's Principles of Internal Medicine Ch. 219 (Parasitic Infections)_