Cats are the true definitive host for which parasite listed below?

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

Answer: (D)

Definitive host means the parasite completes its sexual life cycle in that host. Cats are the true definitive host for Toxoplasma gondii because the parasite undergoes sexual reproduction in the feline intestinal epithelium, producing oocysts that are shed in the cat’s feces. Those oocysts then need time in the environment to sporulate and become infectious, helping spread the parasite to intermediate hosts (including humans) where tissue cysts form.

The other organisms listed do not have cats as the site of their sexual cycle. Balantidium coli and Eimeria stiedae complete their life cycles in their respective primary hosts (pigs for B. coli and rabbits for E. stiedae), and Psoroptes cuniculi is an ectoparasite of rabbits. So, Toxoplasma gondii is the one for which cats are the definitive host.