Case #256 – July, 2009

A 25-year-old refugee from Myanmar was screened for parasites at a local clinic in Tennessee. Stool specimens were collected in 10% formalin and polyvinyl alcohol (PVA) and sent to the state health laboratory for ova and parasite (O&P) work-up. Figures A–D show what was observed in a concentrated wet mount made from the formalin-preserved stool. Figures A and B show what was observed under brightfield microscopy; Figures C and D show the same fields, respectively, observed under UV microscopy. All images were captured at 400x magnification. The objects of interest measured on average 17 micrometers long by eight micrometers wide. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

This was a case of sarcocystosis caused by a member of the genus, Sarcocystis. The two species that cause intestinal sarcocystosis in humans are S. hominis and S. suihominis; the two species cannot be differentiated morphologically. Diagnostic features included:

individual sporocysts within the size range for Sarcocystis spp. (15-20 micrometers long by 8-10 micrometers wide).
the ability of sporocysts to autofluoresce under UV microscopy (Figures C and D).

Usually sporulated oocysts, each containing two sporocysts, are shed in the stool of the definitive host. These oocysts typically measure 15-20 micrometers long by 15-20 micrometers wide. Due to the fragile nature of the oocysts, often individual sporocysts are observed in stool specimens, as seen in this case.