Ascaris lumbricoides

Ascaris lumbricoides. Infertile egg in fecal smear (unstained, high power). In a teenage boy who had immigrated to the United States from Vietnam, the finding in feces of eggs such as this one resulted in the erroneous diagnosis of Paragonimus westermani in a succession of laboratories. What was misleading about this particular egg was that the shell was devoid of mamillations, its contents were disorganized, and there was a vague suggestion of an operculum. Other eggs in the sample showed more conspicuous mamillations in some, as well as other features consistent with a diagnosis of infertile Ascaris.