**Core Concept:** Rectal prolapse is a condition where the internal anal sphincter muscle and surrounding rectal wall protrude through the anus. It may be primary (idiopathic) or secondary to various causes like constipation, straining during defecation, obesity, etc. The clinical presentation includes abdominal pain, distension, bloody or mucus-filled diarrhea, and tenesmus.

**Why the Correct Answer is Right:** The correct answer is **D. Hookworm infection**. Hookworms, particularly Ancylostoma duodenale and Necator americanus, are helminths that can invade the gastrointestinal tract, causing various symptoms and signs depending on the stage of infection. In advanced cases, hookworms can cause rectal prolapse due to their impact on the internal anal sphincter muscle and surrounding rectal wall.

**Why Each Wrong Option is Incorrect:**

A. **E. Coli O157**: Escherichia coli O157 is a common cause of bloody diarrhea and abdominal pain but does not typically cause rectal prolapse.

B. **G. Amoebiasis**: Entamoeba histolytica is the causative agent of amoebiasis and can lead to amebic colitis with dysentery and abdominal pain but does not typically cause rectal prolapse.

C. **I. Schistosomiasis**: Schistosoma species are responsible for schistosomiasis, characterized by abdominal pain, diarrhea, and liver and spleen enlargement, but not rectal prolapse.

**Clinical Pearl:**
The presence of rectal prolapse along with symptoms like abdominal pain, bloody diarrhea, and mucus-filled diarrhea in a patient with hookworm infection, may lead to the correct diagnosis. A detailed medical history, physical examination, and stool examination for eggs are essential to identify the causative agent.

**Correct Answer Explanation:**

D. **Hookworm infection**: Hookworms, particularly Ancylostoma duodenale and Necator americanus, can invade the gastrointestinal tract, leading to symptoms like abdominal pain, bloody diarrhea, and mucus-filled diarrhea. In advanced cases, hookworms can cause rectal prolapse due to their impact on the internal anal sphincter muscle and surrounding rectal wall. This can manifest as a combination of symptoms, including abdominal pain, bloody diarrhea, mucus-filled diarrhea, and rectal prolapse. Stool examination for eggs is crucial in identifying the causative agent.