Case of the Week 597

This week's case is very timely, as we are seeing a lot of these objects in some of our stool specimens submitted for routine ova and parasite exam. They measure approximately 8-10 micrometers in dimension (shown at 500x and 1000x). Identification? What additional stain or study would you like to do?

Answer to Case 597

Answer: Cyclospora cayetanensis oocysts, unsporulated

I figured this was a very timely posting, as we are currently experiencing an outbreak of cyclosporiasis in the Midwestern United States. It's a good reminder to keep an eye out for these round refractile structures in routine stool preparations and follow-up with confirmatory testing (e.g., modified acid fast, modified safranin, examination for autofluorescence, molecular amplification).

I also figured this was a timely case for my United States readers as the confirmatory modified acid fast and safranin stains provide beautiful red, white and blue images for the 4th of July celebrations (American Independence day; my apologies to my British friends)

Here is a gorgeous image from a modified safranin stain of C. cayetanensis oocysts from Florida Fan:
(from Case of the Week 447):

Case of the Week 596

This week's case was donated by Dr. Bobby Boyanton. The images show cross-sections of an appendix from a young girl with chronic abdominal pain. The pathologist became concerned when they saw the following objects within the lumen of the appendix (taken using 4x, 10x, 20x, 20x and 40x objectives, respectively). Identification?

Answer to Case 596

Answer to Parasite Case of the Week 596: Plant material; likely plant epidermis from leafy material. There appears to be a cuticle present, and part of an epidemal cell layer attached.

There are several nice images of dichotomous leaf epidemal structure HERE. Mary Parker, a botanist, noted that "in aqueous conditions, I  would expect an epidermal layer to curl with the cuticle inwards (which is the case in the images) as the cuticle is waterproof and doesn't swell, whereas the epidermal cells would be hydrated and expand forcing the layer into a spiral." Thank you Mary for your valuable input! Mary has also provided assistance with Case 534 in which we showed plant stomata, and Case 468 that showed banana material. Parasitologists and pathologists commonly see food material in fecal and intestinal specimens, as well as in cases of bowel rupture/fistula and food aspiration (i.e., in respiratory specimens). Therefore, it's helpful to have some basic familiarity with how plant material appears in routine preparations. 

Several writers asked if this could be Enterobius vermicularis or Trichuris trichiura. While the size and location may fit with either of these roundworms, the cuticle and attached cellular structure shows some subtle differences that are useful for excluding them. Specifically, the thick acellular roundworm cuticle is adjacent to a muscular layer, as shown in the images below. In comparison, the plant cuticle is adjacent to the boxy cells of the epidemis. I also highlighted some features that are useful for specifically identifying E. vermicularis and T. trichiura (i.e., lateral ala and bacillary band). 

One additional study that would have been helpful in this case would be to use a polarizer to see if the cuticle and cells are birefringent. Plant cell walls often are, whereas nematode cuticles are not.

Thanks again to Bobby Boyanton for donating this interesting case!

Case of the Week 595

This week's case was generously donated by Dr. Marc Couturier and Blaine Mathison. The patient is a young adult male from the South Central United States. No travel history is available. Review of his peripheral blood film reviewed the following:

Identification? What are the structures seen in the last 2 images?

Answer to Case 595

Answer to Parasite Case of the Week 595: Plasmodium vivax with exflagellated microgametocytes. Free microgametes are seen.

The following excellent description was written by Marc Couturier and Blaine Mathison, the contributors of this case.

There are several features of this slide that are supportive for P. vivax.

First, many of the infected cells are reticulocytes (which are larger than mature RBCs), which P. vivax and P. ovale have predilection to infect. Second, the gametocytes are enlarged and fill almost the entire space within the parasitized RBC. Some of the infected RBCs also take the shape of neighbouring RBCs (distorted, pleomorphic); particularly in the areas where cells are dense. Third, the mature schizonts contained upwards of 18-20 merozoites with yellowish brown pigment present, which strongly points toward P. vivax, since the range of P. ovale tends to reach 14 merozoites at maximum. Fourth, some developing trophozoites were grossly amoeboid. Plasmodium ovale usually demonstrates some amoeboid characteristics, but it is usually more exaggerated with P. vivax. Notice also none of the infected RBCs were fimbriated (which, when present supports P. ovale but the absence of which does not rule-out P. ovale).

In the images provided, there was an absence of Schüffner’s stippling. There were some parasitized cells that did display stippling (not shown), but the majority did not. It is important to remember that stippling can be helpful to support an identification, but the absence of stippling does not rule-out the species that usually present with stippling (P. vivax and P. ovale).  Stippling is a pH dependent feature and Giemsa stained slides are the best to display this due to the optimized pH (Wright and Wright-Giemsa are suboptimal for this). 

Overall the RBC morphology was quite good, suggesting that the blood was processed soon after collection. However, we suspected that there was a delay in slide processing which likely led to exflagellation of microgametocytes, with free microgametes seen among the RBCs: 

Exflagellation of microgametocytes in blood specimens post-collection can occur due to multiple factors including decreased temperature, decreased CO2, increased O2 and subsequent increased pH. Free microgametes can be confused with other blood parasites such as Trypanosoma or relapsing fever Borrelia spp. (RFB). The key differences between these organisms are as follows: RFB are thin, faint staining, and in thin films will typically maintain a sinusoidal amplitude. The staining is uniform throughout the length of the bacteria and the width of the spirochetes is also consistent along the length of the organism. As can be seen with the free microgametes, there is irregular amplitude, and chromatin visible within the structure (causing heterogenous thickness).  Trypanosoma spp. on the other hand are irregularly shaped compared to RFB; however, they should be identified based on the presence of a characteristic large nucleus in the central part of the organism, a posteriorly located kinetoplast, a flagellum, and an undulating membrane (not always visible).  The long, slender nature of the microgametes might also be suggestive of microfilariae; however, microfilariae would never be this small. Here is an image of these structures shown side-by-side for comparison:

Case of the Week 594

This week's case was donated by Florida Fan - a lovely classic protozoan parasite seen in a concentrated wet prep of stool, and trichrome-stained specimen. Each line on the scale bar in the first 2 images represents 2.5 micrometers. Identification?

Answer to Case 594

Answer to Parasite Case of the Week 594: Entamoeba coli cysts and trophozoite.

This case shows all of the classic features of Entamoeba coli, with large organisms and, most importantly, cysts that contain more than 4 nuclei. According to the CDC DPDx, "karyosomes may be compact or diffuse and are usually eccentrically located. Peripheral chromatin is present and is often coarse, granular, and irregularly arranged along the nuclear membrane but may be more uniform. The cytoplasm of mature cysts may contain diffuse glycogen. Chromatoid bodies are seen less frequently than in E. histolytica. When present, they are usually splinter like with pointed ends, whereas the chromatoid bodies of E. histolytica have rounded ends. The cytoplasm [of trophozoites] is usually coarsely granular and vacuolated (often described as “dirty” cytoplasm). Pseudopodia may be seen and are often short and blunt."

While I would hesitate to make the diagnosis on any one of these features alone, together they strongly support the diagnosis of E. coli. Again, the presence of >4 nuclei in the cyst is the strongest diagnostic feature.

Thanks again to Florida Fan for donating this classic case!

Case of the Week 593

This week's case is from Idzi Potters and the Institute of Tropical Medicine Antwerp. Warning - it's a tough one! The patient is a young woman with recent travel to the Democratic Republic of the Congo. While there, she worked with primates, and developed a short episode of fever, rash and diarrhea. Upon return to Belgium, a check-up was done, including a stool parasite exam. Apart from Giardia duodenalis and Trichuris trichiura, the following structures were found (measuring about 50 to 55 µm in length). What is your differential diagnosis?