A 5-year-old child presents with intense perianal itching, predominantly during nighttime. Microscopic examination reveals an egg. Which organism is most likely responsible for the condition?
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Child with nighttime perianal itching = Enterobius vermicularis.
Step 1: Understanding the Question:
The hallmark symptom of "intense perianal itching at night" in a young child is highly characteristic of pinworm infection. We need to identify the organism whose egg matches the description and potentially the provided image. Step 2: Detailed Explanation:
Enterobius vermicularis (Pinworm/Seatworm): This is the most common helminthic infection in developed countries and very common in children.
Life Cycle and Symptoms: Gravid female worms migrate out of the anus at night to deposit eggs on the perianal skin. This causes intense pruritus ani. The child scratches the area, gets eggs under their fingernails, and reinfects themselves (auto-infection) or spreads it to others.
Morphology of the Egg: Enterobius eggs have a characteristic shape: they are colorless, "D-shaped" (flattened on one side and convex on the other), and possess a double-layered shell. They contain a coiled larva.
Diagnosis: The standard test is the "Scotch tape test" or "Cellophane tape test," where tape is applied to the perianal area in the morning to capture the eggs for microscopy. Eggs are rarely found in the stool.
Treatment: Albendazole or Mebendazole, often given as a single dose and repeated in two weeks to kill any larvae that hatched from eggs surviving the first dose.
Step 3: Final Answer:
Enterobius vermicularis is the cause of nocturnal pruritus ani, and its eggs are characteristically D-shaped.
