Answer to Case 527

Answer to Parasite Case of the Week 527: Macracanthorhynchus sp., one of the acanthocephalans, or "thorny-headed worms."

Note its relatively large size, and the constrictions that give a false impression of segmentation. My techs call this a bubblegum appearance, which I think you can appreciate in this case:

Macrocanthorhynchus species have a retractable proboscis, which proved to be quite difficult to see in this case. Florida Fan nicely solved this problem by having histologic sections made of the anterior end:

Although I didn't provide enough features for species identification, Florida Fan noted that the morphology is consistent with M. ingens: "The proboscis measures ~500 µm in width and ~650 µm long, much smaller than that of M. hirudinaceus." The geographic distribution (Southeastern United States) also fits with this species. Blaine Mathison, Henry Bishop, Richard Bradbury and others published a very similar case 2 years ago that you can read HERE. It contains a lot of interesting information about the lifecycle, morphologic features and treatment of M. ingens (for example, human infection may be acquired by eating millipedes). Acanthocephalans are more closely related to rotifers than nematodes; hence Blaine's mention of rotifers in the comments.

Florida Fan seems to get a lot of these cases! HERE is one that he donated back in 2013 which nicely shows the eggs of Macracanthorhynchus. You can't tell M. hirudinaceus from M. ingens by its eggs, unfortunately. Take a look at the previous case for more information and a nice poem by Blaine.