Which nematode eggs are commonly described as large, mammillated, and about 45–75 μm in length?

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

Answer: (D)

The key idea is recognizing nematode eggs by size and surface texture. Ascaris lumbricoides eggs are among the largest seen in human stool and have a distinct rough, mammillated outer surface—little wart-like projections on the shell—measuring about 45–75 μm in length. This combination of large size and a mammillated shell is characteristic and helps distinguish them from other common nematode eggs.

For context, Enterobius vermicularis eggs are smaller and have a flattened side with a smoother surface; Trichuris trichiura eggs are barrel-shaped with bipolar plugs; Ancylostoma duodenale eggs are 60–75 μm long but possess a thin, smooth shell without mammillations.