Question
A 30-year-old father visits his doctor after receiving a notice from his child’s daycare about a possible parasitic infection outbreak. The notice mentioned symptoms such as intense itching around the anal area and occasionally seeing tiny worms or eggs near the anus or in stool. Both the father and his child have similar complaints. The physician prescribes a single-dose anti-parasitic drug for all household members along with strict hygiene advice.
Which parasite is the most probable cause of this cluster of infections?
A. Hookworm (Ancylostoma species)
B. Large intestinal roundworm (Ascaris species)
C. Pinworm (Enterobius vermicularis)
D. Threadworm (Strongyloides species)
E. Pork tapeworm (Taenia solium)
Answer
Enterobius vermicularis (Pinworm)
Detailed Explanation
This is a classic presentation of threadworm (pinworm) infection, caused by Enterobius vermicularis.
Key Clinical Clues
- Perianal itching (especially at night) → hallmark symptom
- Affects children + spreads to family members → highly contagious
- Outbreak in nursery/daycare setting → classic epidemiology
- Visible worms or eggs near anus → due to nocturnal migration of female worms
Life Cycle Insight
- Eggs are ingested (via contaminated hands, bedding, toys)
- Larvae hatch in intestine
- Adult worms live in colon
- Female migrates at night to perianal region → lays eggs → itching → scratching → reinfection/spread
This explains:
- Why itching is nocturnal
- Why entire households get infected
- Why hygiene is crucial
Why Other Options Are Wrong
- Ancylostoma duodenale (hookworm)
- Enters via skin (barefoot exposure)
- Causes anemia, GI symptoms
- ❌ No perianal itching or visible worms
- Ascaris lumbricoides
- Large roundworm
- Causes intestinal obstruction, pulmonary migration
- ❌ Eggs passed in stool, no anal itching
- Strongyloides stercoralis
- Skin penetration, autoinfection cycle
- Seen in immunocompromised
- ❌ No classic perianal itching
- Taenia solium (pork tapeworm)
- From undercooked pork
- Causes cysticercosis
- ❌ No nursery outbreaks or itching
Cheat Sheet (Exam Gold)
- Organism: Enterobius vermicularis
- Common name: Pinworm / Threadworm
- Transmission: Fecal-oral (hand → mouth)
- Classic symptom: Night-time perianal itching
- Epidemiology: Children, daycare outbreaks
- Diagnosis:
- Tape test (eggs)
- Often clinical
- Treatment:
- Mebendazole (single dose)
- Treat ALL household members
- Prevention:
- Hand hygiene
- Trim nails
- Wash bedding/clothes
Flashcards
Q1. What is the most common helminth infection in children in developed countries?
A: Enterobius vermicularis
Explanation: Highly contagious and common in schools/daycare
Q2. Why does itching occur at night in pinworm infection?
A: Female worms migrate to lay eggs at night
Explanation: Causes irritation → itching
Q3. What is the diagnostic test for pinworm?
A: Sellotape (tape) test
Explanation: Eggs collected from perianal area
Q4. Why treat all household members?
A: High reinfection and transmission risk
Explanation: Eggs spread easily via contact
Q5. First-line drug?
A: Mebendazole
Explanation: Single dose usually effective
MCQs (High-Level Practice)
MCQ 1
A child presents with nocturnal anal itching. What is the most appropriate initial management?
A. Stool microscopy
B. Empirical mebendazole for child only
C. Empirical treatment for entire household
D. Colonoscopy
E. Antibiotics
Answer: C
Explanation: Treat all household members to prevent reinfection.
MCQ 2
Which feature is most specific for Enterobius infection?
A. Iron deficiency anemia
B. Pulmonary migration
C. Nocturnal perianal pruritus
D. Hepatosplenomegaly
E. Bloody diarrhea
Answer: C
Explanation: Classic hallmark symptom.
MCQ 3 (False question)
Which of the following is FALSE regarding Enterobius vermicularis?
A. Transmission is fecal-oral
B. Female lays eggs around anus
C. Infection spreads easily in families
D. Worm penetrates skin to infect host
E. Itching is worse at night
Answer: D
Explanation: Skin penetration is seen in hookworms, not Enterobius.
MCQ 4
Which investigation confirms pinworm infection?
A. Blood eosinophils
B. Stool culture
C. Tape test
D. CT abdomen
E. PCR
Answer: C
Explanation: Eggs collected from perianal region.
MCQ 5
Which parasite is most associated with anemia due to blood loss?
A. Enterobius vermicularis
B. Ancylostoma duodenale
C. Ascaris lumbricoides
D. Taenia solium
E. Strongyloides stercoralis
Answer: B
Explanation: Hookworms attach to intestinal mucosa and suck blood.
MCQ 6
Why is reinfection common in pinworm infection?
A. Eggs survive in bloodstream
B. Eggs are airborne
C. Poor hygiene → hand-to-mouth cycle
D. Parasite multiplies in liver
E. Drug resistance
Answer: C
Explanation: Autoinfection via scratching and ingestion.
Summary for Quick Exam Revision
Enterobius vermicularis (pinworm) is the most common helminth infection in children, especially in developed countries. It spreads via the fecal-oral route, commonly in daycare or school environments, and easily infects entire households. The hallmark feature is nocturnal perianal itching caused by female worms migrating to lay eggs around the anus at night. Diagnosis is usually clinical but can be confirmed using the tape test. Treatment is with a single dose of mebendazole, and all household members must be treated simultaneously to prevent reinfection. Strict hygiene measures such as handwashing, nail trimming, and washing bedding are essential. Unlike other helminths, pinworms do not invade tissues, do not cause anemia, and are confined to the gastrointestinal tract. The key differentiator in exams is the combination of itching, family spread, and daycare outbreaks.