Which parasite has cats as the true definitive host in its life cycle?

• A. Balantidium coli
• B. Eimeria stiedae
• C. Psoroptes cuniculi
• D. Toxoplasma gondii

Answer: (D)

Definitive host is the host in which the parasite undergoes sexual reproduction. Toxoplasma gondii is unique in that its sexual cycle occurs only in felines, especially domestic cats. When a cat ingests tissue cysts from an infected animal, the parasite completes its sexual development in the cat’s intestinal lining and produces oocysts that are shed in the feces. These oocysts then sporulate in the environment and become infectious, allowing transmission to intermediate hosts like humans, rodents, or birds. Because the sexual part of its life cycle happens in cats, they are the true definitive host for Toxoplasma gondii. The other organisms listed have their sexual cycles in other hosts or do not rely on cats for their definitive host, so they don’t fit this question.