Answer to Case 795

Answer to the Parasite Case of the Week 795: Taenia saginata/suihominis gravid proglottid. 

As noted by Anonymous, Patrik, Antoine A, Florida Fan, Menzler, and others, we have a proglottid of Taenia saginata/Taenia suihominis (formerly known as T. asiatica) characterized by >12-13 primary uterine branches on each side of the central uterine stem and a Taenia spp. egg characterized by an internal hooked oncoschere and a thick radially striated outer shell. Assuming the image of the egg was acquired using a 40x objective, we can estimate a size of 35 micrometers in greatest dimension which is consistent with Taenia species. We don't have a patient travel history, so I would sign this case out as "Taenia saginata/Taenia suihominis". 

This beautiful preparation shows a fresh proglottid pressed between glass and backlit to show the characteristic branching pattern. I particularly like this technique since it requires only minimal manipulation of the proglottid. It can easily be done with a fresh proglottid, but preserved proglottids need to be cleared and softened through exposure to lactophenol or other preparation. 

Injecting India ink into the lateral genital pore of Taenia proglottids can also be used to highlight the uterine branches, but we don't perform this in my lab given the potential infectious risk associated with T. solium.

Regarding motility as a diagnostic feature - I dug into this in Case of the Week 789 by scouring the old literature and found only anecdotal evidence. However, it does seem that Taenia saginata proglottids are more likely to be motile than T. solium. I can't speak to T. suihominis, so if anyone has information to share on this species, I would love to hear it. 

Thanks again to Idzi and Loranne for donating this great case!