**Core Concept**
Cysticercosis is a parasitic infection caused by the larval stage of a tapeworm. Specifically, it is a neurocysticercosis when the larvae infect the central nervous system. The causative agent is a parasite that undergoes a complex life cycle involving a definitive host (typically a carnivore) and an intermediate host (usually a human).

**Why the Correct Answer is Right**
The correct answer is **Taenia solium**, a species of tapeworm. The life cycle of T. solium begins when an individual ingests undercooked pork containing the cysticercoid larvae of the parasite. The larvae then migrate to various tissues, including the brain, where they develop into cysts, leading to cysticercosis. Infection with T. solium can occur through the fecal-oral route, where individuals ingest contaminated feces or food and water contaminated with the tapeworm eggs.

**Why Each Wrong Option is Incorrect**
* **Option A:** Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis, not cysticercosis.
* **Option B:** Echinococcus granulosus is a tapeworm that causes echinococcosis or hydatid disease, not cysticercosis.
* **Option C:** Ascaris lumbricoides is a nematode worm that causes ascariasis, not cysticercosis.

**Clinical Pearl / High-Yield Fact**
Cysticercosis is a significant public health problem in many parts of the world, particularly in areas where sanitation and hygiene are poor. Individuals with cysticercosis may present with a range of symptoms, including seizures, headaches, and cognitive impairment, depending on the location and number of cysts.

**Correct Answer: D. Taenia solium**