Answer to Parasite Case of the Week 623: Wuchereria bancrofti microfilariae
This case showed all of the classic features of W. bancrofti microfilariae, including the sheath which was nicely highlighted by the Delafield's hematoxylin stain. The sheath may not always be seen with routine Giemsa stain; when it is present, it often appears as a negatively-staining outline only. The Delafield's hematoxylin isn't routinely performed in the parasitology laboratory, but it is in all of the classic parasitology texts as an option for highlighting microfilariae sheaths. It's a beautiful stain!
Here are the features of interest:
- Presence of a sheath
- Nuclei do not go all the way to the tip (tip is Without nuclei in Wuchereria)
- Width of the microfilaria is about the same or greater than the surrounding WBCs on thin blood films. This is in contrast to Mansonella spp. which are more slender than the WBC diameter on thin films (important when a sheath is not seen).