Man is a definitive host of which parasite ?
**Core Concept**
The question requires the identification of a definitive host, which is a host in which the parasite reaches maturity and reproduces sexually, producing offspring that can be transmitted to the next host. In parasitology, definitive hosts are typically mammals or birds, while intermediate hosts are usually invertebrates or lower vertebrates.
**Why the Correct Answer is Right**
The correct answer is a parasite that has a complex life cycle involving both a definitive host and an intermediate host. In this case, the parasite undergoes asexual reproduction in the intermediate host, and then the infected intermediate host is ingested by the definitive host, where the parasite reaches maturity and reproduces sexually. For example, the parasite *Taenia solium* has a life cycle that involves both pigs (intermediate hosts) and humans (definitive hosts).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because *Ascaris lumbricoides* is an intestinal nematode that has a simple life cycle involving only one host, the human. It does not require an intermediate host to complete its life cycle.
**Option B:** This option is incorrect because *Plasmodium falciparum* is a protozoan parasite that has a complex life cycle involving two hosts, but the human is an intermediate host, not a definitive host. The definitive host of *Plasmodium falciparum* is the mosquito.
**Option C:** This option is incorrect because *Toxoplasma gondii* is a protozoan parasite that has a complex life cycle involving two hosts, but the cat is the definitive host, not the human.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the definitive host of a parasite is where the parasite reaches maturity and reproduces sexually, whereas the intermediate host is where the parasite undergoes asexual reproduction. Understanding the life cycle of a parasite is crucial in diagnosing and treating parasitic infections.
**Correct Answer:** D.