Case #148 – January, 2005

A public health laboratory sent images to DPDx for telediagnosis assistance to confirm their parasite identification of a 160 micrometer long object. The patient was a refugee from Africa. Figure A shows the object in a formalin-ethyl acetate (FEA) concentrated wet mount. What is your diagnosis? Based on what criteria?

Figure A

This was a case schistosomiasis caused Schistosoma intercalatum, as demonstrated by an egg in an FEA concentrated stool specimen. Diagnostic features seen in the images included:

the size of the egg, which was consistent with S. intercalatum (140-240 micrometers). It should be noted that the size range overlaps with that of the morpholigcally-similar, S. haematobium (eggs 112-170 micrometers long).
the shape of the egg, with a prominent equatorial bulge and terminal spine, which is typical for S. intercalatum. Schistosoma haematobium also has a terminal spine, but the egg is generally more evenly rounded.

Eggs of S. intercalatum are typcially found in feces, whereas S. haematobium eggs are usually found in urine. If proper specimen collection techniques are not followed, it is possible for urine to contaminate a fecal specimen, so careful observation of morphologic features is important.