Which parasite is not zoonotic?

• A. Giardia
• B. Toxoplasma
• C. Echinococcus
• D. Dipylidium

Answer: (C)

Zoonosis means a parasite can be transmitted from animals to humans. Each parasite listed has documented potential to infect people, though how often this occurs varies.

Giardia can infect humans and many animals, with transmission through contaminated water or food; it’s recognized as zoonotic because animal strains can infect people. Toxoplasma gondii is classic for human infection via cat feces or undercooked meat, illustrating how a parasite that cycles in animals can reach humans. Echinococcus tapeworms rely on dogs or other canids as definitive hosts, and humans become accidental hosts by ingesting eggs, leading to hydatid disease—again a clear zoonosis. Dipylidium caninum involves fleas as an intermediate host, with humans occasionally acquiring infection by accidentally swallowing an infected flea, so it is also considered zoonotic, though relatively rare.

Because each of these parasites can reach humans from animal sources, there isn’t a true non-zoonotic option among them. If a question asks which is not zoonotic, it reflects a misleading or flawed prompt, since all listed parasites have demonstrated zoonotic potential.