Answer to Case 637

 Answer to Parasite Case of the Week 637: Schistosoma intercalatum

This was definitely a tricky case! The eggs strongly resemble those of Schistosoma haematobium, but stool would be an unusual source for this parasite, and the eggs in this case are larger than what would be expected for S. haematobium (usual size is 110 to 170 micrometers long). In comparison, S. intercalatum eggs are most often found in stool and measure 140 to 240 micrometers long. They also characteristically have an equatorial bulge as seen in one of the images from this case:

Of note, Schistosoma intercalatum has a very limited geographic distribution, being found primarily in the Congo area. Therefore, getting a travel history can be extremely helpful. As Marc Couturier pointed out on Twitter, the other major consideration is S. guineensis due to the morphologic similarities of the eggs of the two species. If a location had not been provided, then reporting out "Schistosoma intercalatum/S. guineensis" would be best.