Monday, March 25, 2024

Case of the Week 742

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 ยตm 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?

Monday, March 18, 2024

Case of the Week 741

Wow, we are already on our 3rd filarial case! The following lovely case from Idzi Potters and the Institute of Tropical Medicine, Antwerp, is another microfilaria found in blood. 

The patient is a middle aged male farmer from Central America who was noted to have mild eosinophilia on routine complete blood count. He is otherwise asymptomatic. The microfilariae measure approximately 175 micrometers in length. What is your identification?






Sunday, March 17, 2024

Answer to Case 741

 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 default. 

To confirm this, we would look at the tail to see if the nuclei go to the tip (M. perstans) or not (M. ozzardi). It's a bit hard to tell in this case, but if you look closely, you can see that the nuclei DON'T go to the tip of the tail. So - Mansonella ozzardi, it is!

Congratulations to those of you who were able to get to Mansonella species. The microfilariae can be hard to identify, so this is definitely advanced  parasitology!

Monday, March 11, 2024

Case of the Week 740

Welcome to our next filarial case by Idzi Potters and the Institute of Tropical Medicine, Antwerp. This week features the following lovely microfilariae seen in a Giemsa-stained thick blood film. They measure approximately 220 micrometers in length. Identification?





Sunday, March 10, 2024

Answer to Case 740

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. 

Sunday, March 3, 2024

It's Finally Here - Filariasis Month with Idzi Potters! Case of the Week 739

Dear Readers,

Welcome to Filariasis Month! We will actually have TWO months of filariae for you as there are so many to cover and so many beautiful cases by Idzi and the Institute of Tropical Medicine, Antwerp.

Idzi and I thought that we should start out with an 'easy' one. The following objects were seen on a blood smear from a patient living in Gabon. They are approximately 250 micrometers long. What is your identification? Bonus question: what additional laboratory test is important for guiding treatment?



Giemsa stained blood films:


Carazzi stain, Knott's concentration:


Saturday, March 2, 2024

Answer to Case 739

 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 is likely to be one of the Mansonella species. Mansonella are not sheathed, small, and quite narrow. Their width is smaller than the diameter of a neutrophil or eosinophil. If, on the other hand, the microfilariae are relatively large (>200 micrometers), then you are dealing with Wuchereria bancrofti, Loa loa, or one of the Brugia species. These are sheathed microfilariae, but the sheath may not always be readily visible on Giemsa stain. Therefore, the size is a more reliable diagnostic feature. To better visualize the sheath, a hematoxylin stain can be performed such as the Carazzi or Delafield hematoxylin stain. (Note: the hematoxylin and eosin stain used in histopathology preparations can also be used, so if you don't have a hematoxylin stain for microfilariae, you can ask for help from your friends in anatomic pathology!)  These larger microfilariae can then be differentiated by characteristics of their head and tail spaces. 

With that introduction, let's turn to the specifics of this week's case. I forgot to provide the length - my apologies! - I've now added it to the case description (~250 micrometers long). You can also get a general sense of the size of the microfilariae by comparing their diameter to the surrounding white blood cells. Note in this image below that the width of sheathed microfilariae such as Loa loa is slightly greater than the diameter of the neighboring eosinophils. Also, there is a hint of sheath (arrows). In contrast, the Mansonella perstans microfilaria in the image on the right is narrower than the surrounding eosinophils. 

Importantly, you can also see a sheath with the Carazzi stain that Idzi provided. Therefore, we can rule out the two Mansonella species found in blood by this finding alone. 

Note that the nuclei go to the tip of the tail, which makes this a classic case of Loa loa. (one of my favorite memory aids is that the nuclei 'flow-a flow-a to the tip in Loa loa). 


To answer my second question - the additional study that should be considered in this case is calculation of the microfilarial burden since patients with >8,000 microfilariae/mL are at risk of encephalopathy when treated with diethylcarbamazine (DEC).

Thanks again to Idzi Potters and the Institute of Tropical Medicine, Antwerp, for this great case! The next case will come out early next week.


 


Wednesday, February 14, 2024

Get Ready for Filariae!

Dear Readers, I'm delighted to announce that March and April are Filariasis Months courtesy of Idzi Potters and the Institute of Tropical Medicine in Antwerp! 


Image by Blaine Mathison

You may want to brush up on your filariae/microfilariae diagnostic skills in preparation. Here are a few resources to help you:

  1.  World Health Organization Bench Aids for the Diagnosis of Filarial Infections. Available here: https://www.cdc.gov/dpdx/diagnosticprocedures/index.html (see the section on filariasis near the bottom right of the page)
  2. CDC DPDx - Laboratory Identification of Parasites of Public Health Concern:
  3. Mathison, Couturier, and Pritt Diagnostic Identification and Differentiation of Microfilariae. J Clin Microbiol 2019. https://journals.asm.org/doi/10.1128/jcm.00706-19
Stay tuned for more!

Wednesday, February 7, 2024

Case of the Week 738

This week's case was donated by Dr. Sheldon Campbell. The following object was noted in fresh sole.   

Interestingly, it was still alive!

 What parasite is present here? 

After carefully removing the worms, the sole was breaded in cornmeal and fried. Looks delicious! 
Would you eat this?

Tuesday, February 6, 2024

Answer to Case 738

Answer to the Parasite Case of the Week 738:  Probable anisakid larva in fresh fish (sole). This is a great reminder to cook your fish well before eating! Alternatively, freeze it for 7 days at -20 C before eating it raw. The final dish that Dr. Campbell created looked quite tasty (sans worms). 

Not just a few readers noted that they might have some hesitation in eating the final product. ๐Ÿ˜‚

One reader commented that generous application of lemon juice to the thawed fish prior to cooking does a great job in removing any live worms (and may result in a mass exodus!) However, this is only a good solution if you like the taste of lemon ๐Ÿ‹.

Thanks again to Dr. Campbell for sharing this great case!