This week's case was generously donated by Dr. José Poloni. The following was found in a stool specimen. Identification? Significance?
(you may need to click twice on the video below to play)
A parasitologist's view of the world
This week's case was generously donated by Dr. Neil Anderson. The following structure was retrieved from the common bile duct during endoscopic retrograde cholangiopancreatography (ERCP). The patient is a refugee from Tanzania who presented with intermittent abdominal pain, distended gallbladder and hepatosplenomegaly. This was one of many "worm like" structures noted on ERCP. Unfortunately this object appeared to tear during removal. The portion submitted measures several centimeters in length. No identifying external structures were identified.
Dr. Anderson's team tried to express eggs from this structure but was unsuccessful. In an effort to learn more about the nature of this object, a portion of it was submitted for histopathologic processing. Representative sections revealed the following:
What is the most likely identification?
Answer to Parasite Case of the Week 633: Fasciola hepatica
Although the fluke was sadly torn in half during retrieval, it has all of the features that allows us to identify it:
As a trematode - it has the flat, leaf-like body shape of a platyhelminth belonging to the Trematoda phylum. On histopathologic examination, trematodes have an outer tegument (with microvillus border, and often with spines), spongy parenchyma with no large cavities, and a digestive tract. Cestodes have a similar appearance, but may have a large cavity (depending on the species and stage), do NOT have a digestive tract or tegumental spines, and have calcareous corpuscles in the stroma.
I don't believe I see see ovarian tubules in this section, although it is hard to tell from this image alone. I also don't see any eggs. This would make sense as Dr. Anderson was not able to express any eggs from the portion of the fluke that he received in the laboratory.
As Fasciola hepatica specifically - the large size of this structure allows us to identify it as either Fasciola hepatica or F. gigantica. We can further identify this fluke as F. hepatica based on the presence of pointed tegumental spines. F. gigantica, in comparison, has tegumental spines with blunt/flattened ends. Other morphologic features (e.g., overall size of the adult and its eggs, features of the acetabulum) can also be used to differentiate F. hepatica and F. gigantica.
Thanks again to Dr. Anderson for sharing this case with us!
This week's case has a fun little twist. The following structures were seen within the mucosa in an intestinal biopsy (hematoxylin and eosin stained) of a patient in sub-Saharan Africa. The largest of these measured >120 micrometers long.
Answer to Parasite Case of the Week 632: Schistosoma mansoni eggs. An adult fluke is also seen - yikes! Note that the eggs are very 'fresh' appearing, with large viable-looking nuclei. This is very different than old calcified eggs that may also be seen in tissue sections. The egg has a prominent lateral spine present which allows us to provide a species-level identification:Case of the Week 522 show great examples of artifactual distortion, and also shows male and female adults together in their characteristic configuration within venules.
Answer: Trichuris trichiura (whipworm), male
As nicely pointed out by Florida Fan, "No, this worm is not so straight. It’s totally so convoluted like the whip of “Dr. Jones” in the movie . Such a beautiful sample with all the identification details including that curved tail and copulatory spicule specific to its sex. No trick, just Trichuris trichura. This is a classic case."
Here are some of the key identifying features:
The following are images from a stool agar culture after 3 days of incubation at room temperature. The patient has persistent peripheral eosinophilia and mild intestinal complaints.
Answer to the Parasite Case of the Week 630: nematode larvae; primary differential is Strongyloides sp., hookworm, Trichostrongylus, and free-living nematodes (e.g., Rhabditis sp.).
The agar plate culture (a.k.a., Koga plate) is a relatively safe and straight-forward method to increase detection of S. stercoralis in feces, and can also be used to culture other nematodes by allowing the eggs in feces to hatch and mature. The procedure is performed by placing a small amount of stool (as shown here) in the center of a nutrient agar. Any agar that supports the growth of enteric bacteria will do, including sheep blood agar and Mueller Hinton agar. We make our own in-house agar using beef broth. If larvae are present in the specimen, they will move over the agar and carry bacteria from the feces with them. The bacteria grow in their tracks, leaving a visible trail of their journeys. Our technologists examine the plates daily for these serpiginous tracks of bacteria. If they are seen, they examine the plate under a light microscope (4x or 10x objective) to look for larvae. HERE is a link to the publication by Dr. Koga detailing the modified agar culture method that we use in our lab.
This case didn't have very pronounced bacterial tracks. However, you can see great examples in some of my previous cases:
Wow, I didn't realize how many cases I've posted of this over the years!
As Marc mentions, the next step is to examine the larvae to identify the genus present, since other nematode eggs in the stool can hatch over a period of days and produce similar-appearing larvae. Free-living larvae may also be present if the fecal specimen was contaminated with soil (which would be unlikely in this case).
To safely examine the larvae, we flood the plate with formalin and let it sit for several minutes. We then carefully remove some of the peripheral material on the plate and place it on a slide to examine microscopically.
This case was particularly remarkable because many of the larvae had matured to be free-living Strongyloides adults. We saw both males and gravid females! You can actually see them on the agar itself, which is really impressive. We suspect that the stool was not submitted immediately after passage by the patient, thus explaining the presence of these advanced forms.
Gravid free-living females:
Adults seen on the plate:
The last question to answer is whether these are S. stercoralis or S. fuelleborni - but that is a subject for a future post!