Answer to Case 744

 Answer to the Parasite Case of the Week 744: Mansonella perstans microfilariae.

As described by Florida Fan, "This is a rather small microfilaria, its width is only about half the diameter of the surrounding neutrophils. The Carrazi stain [a hematoxylin-based stain] did not show a sheath either. As such, we can definitely rule out all the sheathed and large microfilaria. We know that we are dealing with Mansonella species. The tail of this Mansonella is not curved , this allows us to eliminate Mansonella streptocerca (strepto = curved, cerca = tail) [and also the source is not tissue]. The tail is also not pointed, this rules out Mansonella ozzardi. We only have one left with a blunt tail: Mansonella perstans which persists." 

This image nicely shows all of these features:

You have all done a great job learning to differentiate the small, unsheathed blood microfilariae (i.e. Mansonella perstans and M. ozzardi) from the larger, sheathed microfilariae. 

Of course, co-infections can occur, and the following is a stunning photograph of M. perstans and Loa loa co-infection. I think we can all appreciated that the Loa loa microfilaria is the top based on its larger size and sheath. 

Thank you for these outstanding cases, Idzi!

Next week we will finish up with the tissue microfilariae. Will you be able to tell them apart?