We have moved onto microfilariae found in SKIN SNIPS - what fun! There are only a couple to choose from. Can you tell which one this is? The microfilariae are approximately 200 micrometers long. Carazzi stain Giemsa stain ..read more

 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]. T ..read more

 We are in the home stretch for the microfilariae! Can you believe that we have just a few more to go? (Unless I decide to repeat some ?)  This week's case shows microfilariae that are approximately 200 micrometers long. The patient is a resident of Brazil and has moderate peripheral eosinophilia. He is otherwise asymptomatic.  Carazzi stain (Knott's concentration): Giemsa stain (thick blood film ..read more

 Answer to the Parasite Case of the Week 743: Brugia timori microfilariae. This was one of the tougher cases, but everyone did a great job narrowing the differential to Brugia. As noted by Florida Fan and Anonymous, we can immediately rule out Mansonella species based on the small size (length and diameter) of the microfilariae. Florida Fan also notes that the sheath is visible, confirming that we are dealing with Loa loa, Wuchereria bancrofti or the Brugia genus.  He then details his method for coming to an exact diagnosis: "First the column of nuclei is so compact that we can ..read more

Welcome back for more microfilariae from Idzi Potters and the Institute of Tropical Medicine, Antwerp. The following microfilariae were seen in Giemsa-stained thick blood films from a man living on Alor Island, Indonesia. They measure approximately 305-315 micrometers in length.  What is your identification? What is your primary differential ..read more

 Answer to the Parasite Case of the Week 742: Wuchereria bancrofti microfilariae. I really enjoyed reading the comments on this case. FloridaFan provided this excellent description of his approach to microfilariae identification: "First the width of the worm is about the same as that of the surrounding neutrophils. Second, its length is greater than 200 micrometers. Third, it has a sheath. Now we know we are dealing with Loa loa, Wuchereria, or the Brugia ones, not with any little pesky Brugia. The next consideration is that the column of nuclei is continuous, the terminal nuclei are not ..read more

This week's case features another beautiful example of microfilariae in blood. The patient is from sub-Saharan Africa and presents with chronic swelling of his left leg. The microfilariae measure approximately 270 µm in length.  Carazzi stain (Knott's concentration): Giemsa Stain (thick blood film) What is your identification? What time should blood be collected for this examination ..read more

 Answer to the Parasite Case of the Week 741: Mansonella ozzardi As many of you noted, we can get to an identification of Mansonella sp. by the small size (length of just 175 micrometers, and the width less than the surrounding white blood cells). There is also no visible sheath, which is supportive of the diagnosis.  So the next question is - which Mansonella is present?? As FloridaFan mentioned, the tip of the tail is pointed rather than blunt, which leads us away from M. perstans. Also, the source is not skin snips, so M. streptocerca is unlikely. That leaves M. ozzardi by de ..read more

Answer to the Parasite Case of the Week 741: Brugia malayi  Thanks to everyone who wrote in. This is one of my favorite microfilariae!  This case had 2 classic features that facilitated the identification: the pink sheath and separation of the 2 terminal nuclei in the tail (see arrows below).  As I noted in the case last week, the sheath isn't always seen. Therefore, the larger length and tail nuclei configuration can allow for the identification, even when the sheath is absent.  ..read more

 Answer to Parasite Case of the Week 739: Loa loa microfilariae Thanks to everyone who wrote in with comments. We received a lot of different responses including some of the sheathed and unsheathed microfilariae. Therefore, this is a great time to review my approach to identifying microfilariae in blood specimens. You can also read this article I wrote with Blaine Mathison and Marc Couturier that provides a diagnostic algorithm for microfilariae in blood. In this algorithm, we recommend first measuring the length of the microfilariae. If they are small (<200 micrometers long), then it ..read more