Case #390 – February 2015

Case Description

A 55-year-old refugee from the Democratic Republic of Congo demonstrated 23.9% eosinophilia with the presence of suspect microfilaria on Wright-Giemsa stained peripheral blood smears. Smears were sent to CDC for confirmation and species identification. Figures A and C show two of the suspect organisms objects observed at 500x magnification with oil; Figures B and C are of the same objects at 1000x magnification with oil. The size of the objects measured 193 micrometers on average. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

This was a case of mansonellosis caused by Mansonella perstans. Diagnostic morphologic features included:

small, unsheathed microfilariae within the size range for the species (normal range is 190-200 micrometers in length; however shrinkage can occur with processing).
microfilariae with a compact column of nuclei.
a blunt tail that contains nuclei to the end of the tail.

In the DRC, M. perstans is similar to ‘Microfilaria’ semiclarum, an enigmatic species of uncertain affinities. Microfilariae of ‘Microfilaria’ semiclarum are larger (198-221 μm long, on average) and have a clear area measuring approximately 40 μm mid-body that is nearly devoid of nuclei, possessing only a few large, scattered nuclei.