Case #239 – November, 2008

A 50-year-old man went to his health care provider after a week of intermittent diarrhea, cramps and nausea. Stool specimens were collected over three consecutive days and sent to the local public health laboratory for routine ova and parasite (O&P) work-up. Figures A–C show objects observed at 1000x magnification on a trichrome-stained slide prepared from the stool specimens. The objects measured approximately 12 micrometers in length. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

The objects observed in this case were trophozoites of the flagellate, Chilomastix mesnili (although flagella may not be visible in stained specimens). Even though C. mesnili is considered nonpathogenic, it should be reported in all routine O&P testing. The presence of C. mesnili in stool specimens could indicate fecal contamination of a food or water source and be an indicator for the presence of other pathogens. The diagnostic features for C. mesnili included:

trophozoites within the size range (6-24 µm long) of the species, possessing a thicker anterior end and a posterior end tapering to a point.
a single nucleus containing a large, eccentric karyosome, located at the anterior end of the trophozoites.