Answer to Case 434

Answer: Enterobius vermicularis (pinworm) eggs

Note the characteristic features including the thin colorless shell and partially-oval shape that is flattened on one side. The larvae are not fully developed within these eggs, but generally are developed (and infective) within 4-6 hours of the eggs being laid.

This was an interesting case in that the eggs were seen in stool rather on a peri-anal adhesive tape preparation. The latter is the preferred method for detecting pinworm eggs since the adult female lays her eggs on the perianal skin folds. However, eggs may attach to the stool as it passes through the anus, and are therefore occasionally (but not reliably!) seen using the ova and parasite exam.