Answer to Case 653

 Answer to the Parasite Case of the Week 653: Not a human parasite; most likely a mucus cast.

As noted by Florida Fan, "The object did not have any internal organization nor visible external anatomy. It displays a ribbon like morphology being flat and slender especially at the bend." 

Sam had a similar thought and suggested that since the "patient had cystic fibrosis it may be some kind of mucous plug."  

To test these hypotheses, we can gently manipulate the object. Mucus usually separates easily whereas a true nematode has a firm, rubbery cuticle and is harder to tear. As CA noted, although not a first choice, we could also put a section through for histopathology. Histopathologic examination can be extremely helpful in several instances, such as when looking for the characteristic lateral cords of the anisakids (see Case of the Week 177) or the uterine branches of Taenia spp. proglottids (See Case of the Week 361).

Thanks again to Drs. Ribes and Fenwick for donating this interesting case!