Case #252 – May, 2009

A 29-year-old man from Haiti had blood drawn for routine work-up, following hospitalization for complications with a congenital disorder. The blood was collected in EDTA tubes and sent to Hematology and Microbiology for evaluation. The following images show what was observed on a Giemsa-stained thick smear of the blood. The object measured 270 micrometers in length. The image in Figure A was captured at 500x magnification; the images in Figures B and C, which show close-ups of the two ends of the same object, were taken at 1000x magnification. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

This was a case of filariasis caused by Wuchereria bancrofti. Diagnostic features included:

a microfilaria within the size range (240-300 micrometers) for W. bancrofti.
a loosely-packed nuclear column.
a tail that tapers to a point, with nuclei terminating before the end of the tail (Figure C).

Although the specimen presented in this case was unsheathed (microfilariae of W. bancrofti usually possess a sheath), the size, nuclear structure, and travel history should make for an accurate diagnosis.