Which of the following parasites requires seafood as a source of infection?

Anisakis simplex is a parasitic nematode that specifically requires seafood, particularly fish and marine mammals, as a source of infection. This parasite can infect humans who consume raw or undercooked seafood, leading to a condition known as anisakiasis. This is a key reason why Anisakis simplex is the correct answer; its life cycle is directly tied to marine organisms, and it can reside in various fish species commonly consumed by people.

Giardia lamblia and Cryptosporidium parvum are both protozoan parasites associated with waterborne illnesses and are typically transmitted through contaminated water rather than seafood. Toxoplasma gondii, while it can be transmitted through various means, primarily spreads through undercooked meats and contaminated foods rather than specifically through seafood. Understanding the specific transmission routes of these parasites is crucial for implementing food safety practices and minimizing the risk of infection.