Oval eggs with a thin shell, flattened side, and containing a curved larva were found in a first-morning urine from a 6-year-old child. They measured approximately 52 μm in length. What is the most likely identification?

Oval eggs with a thin shell, flattened side, and containing a curved larva were found in a first-morning urine from a 6-year-old child. They measured approximately 52 μm in length. What is the most likely identification?

• A. Hookworm
• B. Enterobius vermicularis
• C. Schistosoma haematobium
• D. Infertile Ascaris lumbricoides

Answer: (B)

Recognizing pinworm eggs by their distinctive morphology is what's being tested. Enterobius vermicularis eggs are small, about 50–60 μm long, oval with a thin shell, and have a noticeable flattening on one side. Crucially, they contain a developing larva that appears curved inside the shell. Seeing eggs with a flattened surface and a curved larva about this size points to pinworm rather than other intestinal parasites. If you compare to the other options, hookworm eggs are not flat on one side and are typically found in stool, not urine, and they usually show developing larvae after incubation. Schistosoma haematobium eggs have a prominent spine and are larger, and their appearance is not oval with a flattened edge or an internal curved larva. Infertile Ascaris lumbricoides eggs have a thicker shell with a more mamillated surface and do not present with the same flattened shape or internal curved larva. The combination of size, thin shell, one-sided flattening, and an internal curved larva makes Enterobius vermicularis the best identification for these eggs.

Recognizing pinworm eggs by their distinctive morphology is what's being tested. Enterobius vermicularis eggs are small, about 50–60 μm long, oval with a thin shell, and have a noticeable flattening on one side. Crucially, they contain a developing larva that appears curved inside the shell. Seeing eggs with a flattened surface and a curved larva about this size points to pinworm rather than other intestinal parasites.

If you compare to the other options, hookworm eggs are not flat on one side and are typically found in stool, not urine, and they usually show developing larvae after incubation. Schistosoma haematobium eggs have a prominent spine and are larger, and their appearance is not oval with a flattened edge or an internal curved larva. Infertile Ascaris lumbricoides eggs have a thicker shell with a more mamillated surface and do not present with the same flattened shape or internal curved larva.

The combination of size, thin shell, one-sided flattening, and an internal curved larva makes Enterobius vermicularis the best identification for these eggs.