Answer to Case 530

Answer to Case of the Week 530: Sarcocystis sp.; either S. hominis or S. suihominis

Thanks again to Idzi Potters and the Institute of Tropical Medicine, Antwerp, for sharing this case with us. I haven't featured intestinal sarcocystosis on this blog before, and so having these great photographs is a real treat. As Old One, Florida Fan, Blaine and others noted, humans serve as the definitive host for the intestinal form of sarcocystosis and shed sporulated oocysts and sarcocysts in their stool. Both forms are seen in this case:

Oocysts contain 2 sporocysts. Due to their fragile nature, they easily rupture so that free sporocysts are also commonly seen in stool specimens. Humans acquire S. hominis and S. suihominis by ingesting undercooked beef or pork respectively. As a pathology resident, I performed a survey of U.S. beef in collaboration with the USDA and confirmed the results of previous surveys that S. hominis was not present in the U.S. beef supply. Having said that, I still wouldn't recommend eating raw beef! Most cases of intestinal disease are asymptomatic, but infected individuals may experience mild watery diarrhea, fever and chills.

Rarely, humans may also serve as the intermediate host for some Sarcocystis species when ingesting oocysts or sporocysts in contaminated food or water. In this form of disease, sarcocysts form within various muscles in the body, causing transient myalgias, muscle weakness and associated edema. HERE is what a sarcocyst looks like in skeletal muscle (a case of S. cruzi; not a human pathogen).