**Core Concept**
Toxocariasis and neurocysticercosis are parasitic infections that affect the central nervous system (CNS). However, the most common parasitic infestation of the CNS is caused by a different organism. This question requires knowledge of parasitology and neurology.

**Why the Correct Answer is Right**
Toxoplasmosis is the most common CNS parasitic infestation worldwide. It is caused by the protozoan parasite *Toxoplasma gondii*. This parasite infects a wide range of hosts, including humans. In immunocompetent individuals, the infection is usually asymptomatic or mild, but it can cause severe disease in immunocompromised patients. Toxoplasmosis occurs when *Toxoplasma gondii* cysts are ingested through contaminated food or water, or when the parasite is transmitted vertically from mother to fetus during pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Toxocariasis is a parasitic infection caused by the nematode *Toxocara canis*. It primarily affects the muscles, liver, and lungs, but it can also affect the CNS in rare cases. However, it is not the most common CNS parasitic infestation.
**Option B:** Neurocysticercosis is a parasitic infection caused by the tapeworm *Taenia solium*. It primarily affects the CNS and can cause a range of symptoms, from seizures to hydrocephalus. However, it is not the most common CNS parasitic infestation.
**Option C:** Echinococcosis is a parasitic infection caused by the tapeworm *Echinococcus granulosus*. It primarily affects the liver, lungs, and other organs, but it can also affect the CNS in rare cases. However, it is not the most common CNS parasitic infestation.

**Clinical Pearl / High-Yield Fact**
Toxoplasmosis is a significant concern in immunocompromised patients, such as those with HIV/AIDS, and in pregnant women. It can cause severe disease in these populations, highlighting the importance of screening and prevention measures.

**Correct Answer: C. Toxoplasmosis. Toxoplasmosis is the most common CNS parasitic infestation worldwide.**