Answer to Case 813

Answer to the Parasite Case of the Week 813: tapeworm proglottids; gross morphology consistent with Taenia species. 

Thank you all for sharing your approaches to providing further work-up and identification! 

Check out the many excellent responses in the comments. Of them, the comments from HCLM fan, Idzi Potters, and Florida Fan most closely mimic our approach:

1. We first closely examine the proglottids using a dissecting microscope to discern if the submitted object is a true tapeworm or some type of worm mimic (e.g., food material, mucus strands). 
2. During examination, we note the size of the object to help narrow the diagnostic possibilities. In this case, the large size is indicative of either Taenia or a fish tape worm such as Dibothriocephalus. 
3. To differentiate between these 2 groups, we look at the length of the proglottids and any external markers such as the laterally-positioned uterine pore or central uterine rosette. As noted by Idzi, this specimen possesses a lateral pore which is consistent with a Taenia species adult. Having proglottids that are longer than they are wide also points us towards a Taenia species.
4. We then manipulate the proglottids to attempt to express eggs from the proglottids and spin down the fluid form the original container.

Here are the eggs from this case - a great example of Taenia sp. eggs!

Since we cannot differentiate the Taenia species by the eggs alone, we will then try to squeeze a proglottid between two glass slides, or between the inverted lid and base of a Petri dish in order to view the internal uterine structures:

Proglottid manipulation is done with extreme caution since the specimen could be T. solium, in which case the eggs could result in cysticercosis if accidentally ingested. 

Like HLCM fan, we avoid India ink injection since it's a challenging technique and often doesn't work when specimens arrive in ethanol or formalin. However, here is a beautiful example by Rachel Voss, MLS(ASCP):

When we are lucky, we get a nice view of our squashed proglottid like the following:

If we are not able to visualize the branches by transilluminating the proglottid, then we usually try to submit the specimen for histologic sectioning. However, as noted by other readers, one can also attempt to clear the specimen using lactophenol or stain it with carmine. 

Once the uterine branches are visualized, we can count the number of primary branches originating from one side of the central uterine stem; >13 = T. saginata or T. suihominis; <13 = T. solium. 

This case contains >13 branches, so this is good news for the patient and family - there is no associated risk of cysticercosis from the eggs shed into the environment from the host. 

Lastly, molecular testing can be used if there is doubt as to the identification; for example, if the proglottids are immature.

Thank you again for sharing your protocols!

Many thanks to Heather and Emily from my lab for sharing these beautiful photographs!