**Core Concept**
Toxoplasma gondii is a protozoan parasite that can infect a wide range of warm-blooded animals, including humans. The parasite has a unique life cycle that involves a definitive host, where the parasite reproduces sexually, and intermediate hosts, where the parasite undergoes asexual reproduction.

**Why the Correct Answer is Right**
Toxoplasma gondii is the only parasite among the given options that has cats as its definitive host. Cats are the primary reservoir of T. gondii, and they play a crucial role in the parasite's life cycle. When cats ingest infected prey or contaminated feces, the parasite undergoes sexual reproduction in the cat's intestines, producing oocysts that are shed in the cat's feces. These oocysts can then infect other intermediate hosts, such as mice or birds, where the parasite undergoes asexual reproduction.

**Why Each Wrong Option is Incorrect**
**Option B:** Rabies is a viral disease that affects the nervous system of mammals, including dogs, cats, and humans. While cats can transmit rabies, they are not a reservoir for the virus.

**Option C:** Streptocerca infection is caused by the parasitic worm Streptocerca spp., which is transmitted through the bite of infected mosquitoes. Cats are not a reservoir for this parasite.

**Option D:** Plague is a bacterial disease caused by Yersinia pestis, which is transmitted through the bite of infected fleas or direct contact with infected animals. Cats are not a reservoir for the plague bacterium.

**Clinical Pearl / High-Yield Fact**
Toxoplasma gondii infection can have significant consequences for pregnant women, as it can cause congenital toxoplasmosis in the fetus. Therefore, pregnant women should avoid handling cat litter or consuming undercooked meat, which may be contaminated with the parasite.

**✓ Correct Answer: A. toxoplasma gondii**