Which parasite is primarily diagnosed by identifying proglottids or a scolex in stool rather than eggs?

• A. Taenia solium and Taenia saginata (species identification relies on proglottids/scolex or molecular methods)
• B. Giardia lamblia
• C. Diphyllobothrium latum
• D. Enterobius vermicularis

Answer: (A)

The important idea here is that identifying Taenia species relies on the appearance of the parasite’s body parts, not just its eggs. Eggs of Taenia species look very similar under the microscope, so to tell T. solium from T. saginata you need to examine the gravid proglottids or the scolex. If you find a scolex, you can look for features like rostellar hooks (present in T. solium, typically absent in T. saginata). If you have gravid proglottids, counting uterine branches helps distinguish them (T. solium has fewer branches, T. saginata more). Because of this, proglottids or a scolex in stool provide species-level identification for Taenia.

In contrast, Giardia lamblia is diagnosed by identifying cysts or trophozoites in stool, not by proglottids. Diphyllobothrium latum is diagnosed by eggs (and sometimes larvae) in stool, which are distinct from Taenia proglottids. Enterobius vermicularis is diagnosed by finding eggs around the perianal area or via tape prep, not by proglottids or a scolex.