A nematode egg measuring approximately 70 × 50 μm is most consistent with which parasite?

A nematode egg measuring approximately 70 × 50 μm is most consistent with which parasite?

• A. Hookworm
• B. Ascaris lumbricoides
• C. Enterobius vermicularis
• D. Trichuris trichiura

Answer: (B)

Egg size and shell morphology are key clues in identifying nematode eggs seen in stool. An egg around 70 by 50 μm fits Ascaris lumbricoides best, since its eggs are among the largest seen in intestinal nematodes—typically about 60–75 μm long and 40–50 μm wide—with a thick, rough (mamillated) shell. This large, oval shape stands out compared with the others: hookworm eggs are smaller and more uniformly ellipsoidal with a thinner shell; Enterobius vermicularis eggs are smaller, often with a flattened side; Trichuris trichiura eggs are barrel-shaped with a distinctive bipolar plug. Therefore, the size given most closely matches Ascaris lumbricoides.

Egg size and shell morphology are key clues in identifying nematode eggs seen in stool. An egg around 70 by 50 μm fits Ascaris lumbricoides best, since its eggs are among the largest seen in intestinal nematodes—typically about 60–75 μm long and 40–50 μm wide—with a thick, rough (mamillated) shell. This large, oval shape stands out compared with the others: hookworm eggs are smaller and more uniformly ellipsoidal with a thinner shell; Enterobius vermicularis eggs are smaller, often with a flattened side; Trichuris trichiura eggs are barrel-shaped with a distinctive bipolar plug. Therefore, the size given most closely matches Ascaris lumbricoides.