Case of the Week 400

Welcome to our 400th Parasite Case of the Week! To celebrate the 400th case, I thought I would dedicate this post to education in parasitology and share with you 5 of my favorite parasite teaching tools.

1. Embed arthropods and worms in casting resin, using products purchased at your local arts and crafts store. I've used Castin' Craft in the past, but there are other options out there as well. Here is one of my creations - adult Ixodes scapularis ticks (in different stages of engorgement) in a small petri dish:

Embedded arthropods are great for teaching because they are durable (e.g. their legs don't fall off from being manipulated over and over again), and you can easily examine both their dorsal and ventral aspects. If you're feeling really creative, then you can also make them into little works of art - or even jewelry (start a fun new trend). You can buy molds in every shape and size under the sun.

2. Find some anisakids in frozen (or fresh) cod. I have the best luck with Atlantic cod; in every bag of 10 fillets, I usually find at least 1 worm. I let the fillets thaw in the refrigerator and then use blunt dissection to find the coiled larvae. I put the fish (with anisakid) on a plate for display in my teaching lab. It's a great way to get medical students, residents, techs, and clinicians interested in parasitology.

For added fun, have a fish dissecting party! Here are some of my awesome pathology residents, who came up with this idea all on their own.

3. Buy some medicinal leeches (Hirudo medicinalis) at your hospital pharmacy. Like the cod, these also make a great display for a parasite teaching laboratory. You can use them as an example of an ectoparasite, talk about the anticoagulant they produce (hirudin - used medicinally), discuss their fascinating history (past and present) in medicine, and also discuss why it is necessary to give prophylactic antibiotics to recipients of leech therapy (to prevent sepsis with Aeromonas - a commensal bacterium in the gut of medicinal leeches).

Yes, it's a display with shameless 'ick' factor, but it's great for capturing the attention of medical students and clinicians alike.

4. Learn some basic entomology skills. Try dragging for ticks, collecting black fly (Simulium sp.) larvae from a fast-flowing stream (below), or learn how to mount insects professionally for teaching purposes (compliments of Blaine Mathison).

5. Last, but not least, have a parasite potluck, with treats decorated with your favorite (candy) parasites.

Cupcakes by Dr. Rachael Liesman, my Clinical Microbiology fellow:

Malaria cookies by my Education Specialist, Emily Fernholz

Cakes from the Mayo Medical Students! Coconut rectum, Giardia duodenalis, Reduviid bug transmitting Trypanosoma cruzi through its feces, Strongyloides stercoralis on a stool agar culture, and a strawberry cervix.

So for my questions this week: What parasites are associated with a 'coconut rectum' and 'strawberry cervix'?

Answer to Case 400

Answers:

1. Parasite associated with 'coconut rectum' - Trichuris trichiura. This description refers to a prolapsed rectum on which numerous adult worms attached to the rectal mucosa can be seen.

(Image courtesy of the CDC Public Health Image Library)

2. Parasite associated with 'strawberry cervix' - Trichomonas vaginalis. This description refers to the punctate hemorrhages seen on the infected cervix which purportedly look like a strawberry.

(Image courtesy of the CDC Public Health Image Library)

Case of the Week 399

Wow, we're almost at 400 cases! I will have to think of something extra special for next week. Meanwhile, here is classic finding in a trichrome-stained stool specimen (1000x).

Identification?

Answer to Case 399

Answer:  Dientamoeba fragilis

This organism has an overall structure like an amoeba, but has an internalized flagellum, and is therefore most accurately characterized as a flagellate. It is sometimes referred to as an amoeboflagellate. As nicely described by Florida Fan, D. fragilis has a characteristic nucleus with 'fragmented' appearing chromatin. It commonly has 2 nuclei, but may also have 1, as seen in some of the organisms in this case.

Case of the Week 398

We had a number of great arthropod cases in the past few weeks! Here's one that had us stumped for a little while:

The following live objects were noted on a tampon brought in by a female patient to her  gynecologist. The patient also reports that these objects are being shed in her stool and urine.

Examination of the specimen revealed a clearly-used tampon containing the following objects - many that appeared to be superficially embedded in the cotton fibers:

Identification? What additional information would you like?

Answer to Case 389

Answer:  Fly larvae; most likely representing involvement of the tampon in the environment rather than in the patient.

As described by Florida Fan and Anon, this is supported by the presence of different larval stages and a possible pupa with respiratory structures. Pupal casings were also seen, indicating that at least 1 adult fly had hatched. There also appears to be more than 1 genera of fly present.

 

If this had all been in the patient (e.g. facultative or obligatory myiasis), then we would have expected the larvae to be in the same stage and of the same genus, unless there was a wound exposed to the environment which different flies were continuing to lay eggs in.

Discussion with the physician revealed that the patient did not have a wound, and that the tampon had been brought in by the patient, rather than being removed by the physician. Therefore, the most likely explanation for this case is that the tampon had been discarded in an open trash can that was exposed to flies. The patient is now likely traumatized by finding the tampon covered in fly larvae, and is understandably concerned that she is also passing larvae in her urine and vaginal secretions. The best course of action for the physician is to explain the situation and reassure her that she does not have myiasis.

Thank you to Blaine Mathison for helping me accurately describe the flies in this case!

Case of the Week 397

This week's case is a blood specimen from an elderly gentleman from Arkansas. He is asplenic and has received multiple blood transfusions for chronic anemia. Below are images from Wright-Giemsa stained thin films taken by our Clinical Microbiology fellow, Poornima.

Identification?
What is the likely species involved in this case?

Answer to Case 397

Answer: Babesia sp.
Interestingly, this case was identified as Babesia divergens/MO-1 strain by PCR testing. The currently unnamed MO-1 strain (found in Missouri) is closely related to B. divergens, a pathogen of cattle in Europe. Since the description of the MO-1 strain, other B. divergens-like organisms have been detected in Kentucky and Washington states.

The morphology of the B. divergens and B. divergens-like organisms is slightly different than that of B. microti, in that the organisms are usually oval or elliptical and tetrad-forms are more commonly seen. The clinical picture is also slightly different in that patients are generally asplenic and have severe to fatal infections.

Although it would be difficult to differentiate B. divergens-like parasites from B. microti based on morphology alone, the presence of predominantly small elliptical forms with prominent tetrads should raise the suspicion for the former parasite.

Case of the Week 396

This week's case is a peripheral blood smear from a 52 year-old businessman from India. Identification?

Answer to Case 396

Answer:  Plasmodium vivax

Thanks to everyone who wrote in on this case. As nicely described by Florida Fan, Yasir and Antonio, the infected red blood cells are larger than the uninfected neighboring cells and Schuffner's dots (stippling) are present, thus indicating that this is either P. vivax or P. ovale infection. You can then narrow down the choices by noting the ameboid chromatin which is most consistent with P. vivax. Some softer features of P. vivax that are also seen in this case are the 'hugging' or 'molding' of infected cells to neighboring cells and the predominance of rounded rather than oval forms.

Florida Fan does point out that the last picture shows what appears to be fimbriation (jagged edges) which is commonly seen in P. ovale. I However, this is also a rather soft feature when only seen occasionally, and I wouldn't let a single cells with possible fimbriations steer me towards P. ovale if the other features are supportive of P. vivax. (I added this last photo in to see if it would fool anyone and was very happy to see that it didn't! You are all too smart for that).

Finally, the history of travel to India is most consistent with P. vivax infection, since this species is responsible for the majority of malaria cases there (with P. falciparum causing most of the remaining cases). In comparison, reports of P. ovale malaria in India are very rare.