A 6-year old child who presented with perianal pruritus, excoriation of skin and nocturnal enuresis was found to be infected with a parasite causing auto infection. The causative agent is –
**Core Concept**
The question is testing the knowledge of a specific parasite that causes auto-infection, leading to perianal pruritus and other systemic symptoms in a pediatric patient.
**Why the Correct Answer is Right**
The causative agent is likely to be Enterobius vermicularis, also known as the pinworm. This parasite causes auto-infection through the anal-rectal route, leading to perianal pruritus and excoriation of the skin. The nocturnal enuresis is a result of the allergic reaction to the eggs of the parasite. The eggs of the pinworm migrate to the perianal region and cause an intense allergic reaction, leading to the symptoms described. The auto-infection occurs when the child ingests the eggs, usually through fecal-oral transmission.
**Why Each Wrong Option is Incorrect**
* **Option A:** Ascaris lumbricoides is a large intestinal nematode that causes ascariasis, but it does not typically cause auto-infection or perianal pruritus.
* **Option B:** Trichuris trichiura, or the whipworm, causes enterobiasis, but it is not typically associated with auto-infection or nocturnal enuresis.
* **Option C:** Strongyloides stercoralis is a nematode that causes strongyloidiasis, but it does not typically cause perianal pruritus or auto-infection.
**Clinical Pearl / High-Yield Fact**
The pinworm is a common cause of perianal pruritus in children, and the diagnosis can be confirmed by demonstrating the presence of eggs in the perianal region or by a stool examination.
**Correct Answer:** D. Enterobius vermicularis.