## **Core Concept**
Auto-infection refers to the process where a parasite or infectious agent infects the same host from which it originated, often leading to a re-infection or prolonged infection. This concept is crucial in understanding the life cycles of certain parasites and the epidemiology of infectious diseases.

## **Why the Correct Answer is Right**
The correct answer, **D. Taenia solium (pork tapeworm)**, is associated with auto-infection. In the case of Taenia solium, auto-infection can occur when the eggs of the tapeworm are released from the adult worm in the human intestine. These eggs can then hatch into oncospheres, which can penetrate the intestinal wall and develop into cysticerci in various tissues of the body, including the brain, muscles, and eyes. This process is known as internal auto-infection and is a unique feature of Taenia solium infections.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While some protozoa can cause prolonged infections, they are not typically highlighted for auto-infection in the same way as Taenia solium.
- **Option B:** This option is not specified, but generally, not all helminths are known for auto-infection.
- **Option C:** This option is also not specified, but similar to option B, not all parasites are primarily known for their potential for auto-infection.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **neurocysticercosis**, caused by the larval stages of Taenia solium, is a significant cause of adult-onset epilepsy and other neurological disorders worldwide. The diagnosis often requires imaging studies and serological tests. Understanding the potential for auto-infection with Taenia solium is critical for managing and preventing these conditions.

## **Correct Answer:** **D. Taenia solium**