**Core Concept**
Toxoplasmosis is a parasitic infection caused by the protozoan Toxoplasma gondii. The life cycle of T. gondii involves a complex interplay between the parasite, its feline host, and accidental intermediate hosts such as humans. The parasite can infect a wide range of warm-blooded animals, including humans, and can cause significant morbidity and mortality in immunocompromised individuals.

**Why the Correct Answer is Right**
In the context of Toxoplasmosis, humans are considered accidental intermediate hosts. This means that the parasite completes its life cycle in the definitive feline host, but humans can become infected through the ingestion of oocysts shed by cats in their feces, or through the consumption of undercooked meat containing tissue cysts. The parasite then undergoes asexual replication in the human host, leading to the formation of tissue cysts in various organs, including the brain, heart, and muscles.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the role of humans in the life cycle of T. gondii.
**Option B:** This option is incorrect because it suggests that humans are the definitive host of T. gondii, which is not the case.
**Option C:** This option is incorrect because it implies that humans are the primary host of T. gondii, which is not accurate.

**Clinical Pearl / High-Yield Fact**
It is essential to note that Toxoplasmosis can be transmitted from mother to fetus during pregnancy, leading to congenital toxoplasmosis. This highlights the importance of preventing maternal infection during pregnancy through measures such as avoiding contact with cat feces and handling raw meat.

**Correct Answer: D. Accidental intermediate host.**