An egg was found in an iodine wet mount of a fecal concentrate. The egg was oval, thin shelled, and approximately 55 mm in length. The interior showed an embryo in the four-cell stage of development. The most likely identification is:

• A. Strongyloides stercoralis
• B. Trichuris trichiura
• C. Hookworm
• D. Enterobius vermicularis

Answer: (C)

The main idea here is recognizing hookworm eggs by their appearance and what you’d expect to see inside them. The egg is oval and has a thin shell, about 55 μm in length, which fits typical hookworm eggs (Necator americanus or Ancylostoma duodenale). The interior showing an embryo at the four-cell stage confirms active embryonation inside the egg, a common finding for hookworm eggs in prepared fecal concentrates. This combination—oval, thin-shelled egg of roughly 55 μm with a four-cell embryonic stage inside—is characteristic of hookworm eggs.

Trichuris trichiura eggs, in contrast, are barrel-shaped with prominent plugs at each end and a thicker shell. Enterobius vermicularis eggs are smaller, often with a flattened side and a smooth shell, and are usually unembryonated when observed in specimens. Strongyloides stercoralis eggs, if seen, may contain larvae rather than a four-cell embryo, and their appearance differs from this description.