Monday, March 29, 2021

Case of the Week 632

 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.

Then there was this...

Sunday, March 28, 2021

Answer to Case 632

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:

Remember that we must exercise caution when interpreting Schistosoma eggs in tissue since there is often a lot of distortion with production of spiky protrusions that occurs during tissue processing. A true spine should be thick and well-defined (such as in this case). 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. 

Here is the partial longitudinal section of the adult in this case - an unexpected surprise! 

You can make out one of the suckers.

Tuesday, March 23, 2021

Case of the Week 631

 Here is a nice straight-forward case from my laboratory. This worm was found on routine screening colonoscopy. It measures approximately 3.5 cm long. 


What are some of the key identifying features? 

Sunday, March 21, 2021

Answer to Case 631

 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 male is slightly smaller than the female; males are 3.0 to 4.5 cm long, while females are 3.5 to 5.0 cm long. Note that the head is at the skinny end - not what you might think!

Monday, March 15, 2021

Case of the Week 630

 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.

This appearance prompted further examination of the plate by light microscopy, which revealed the following (click on thumbnail for video):

What is your differential diagnosis based on this information?

Sunday, March 14, 2021

Answer to Case 630

 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:

Case of the Week 110 and Answer (S. stercoralis in sputum; microscopic track on our in-house agar)

Case of the Week 112 and Answer (Hookworm in a duodenal aspirate; very clear track on our in-house agar)

Case of the Week 137 and Answer (S. stercoralis tracks on sheep blood agar; this was an incidental finding on bacterial stool culture and shell vial viral culture)

Case of the Week 151 and Answer (video of S. stercoralis larvae and tracks on our in-house agar)

Case of the Week 218 and Answer (video of S. stercoralis larvae in agar)

Case of the Week 337 and Answer (S. stercoralis; incidental finding on bacterial stool culture: sheep blood agar and McConkey agar)

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!

Tuesday, March 9, 2021

Case of the Week 629

 This week's case is from my laboratory. The following structures were found in a concentrated stool specimen from a middle-aged man from Ethiopia. They measure approximately 65 micrometers in length. What is the most-likely identification?

Sunday, March 7, 2021

Answer to Case 629

 Answer to Parasite Case of the Week 629: hookworm ova - either Ancylostoma duodenale or Necator americanus

As stated well by Sam, "Finally! An end to the "is this hookworm?" trilogy. Haha 😁"  You can see a couple of good examples of hookworm egg mimics in my last two cases.

He and TheOracle also noted that the second image had Charcot-Leyden crystals, a breakdown product of eosinophils:

Idzi commented that "If you would ask for the "most-likely" identification, I'd dare guessing "Ancylostoma duodenale" - not per sé due to the fact that the patient is from the African continent (as migration and travel have mixed A.duodenale and N. americanus geographically up), but the second picture shows an egg with a very low number of blastomeres (only 4!). This low level of cleavage in freshly produced feces is more typical for A. duodenale. Necator usually has "already" about 8 blastomeres in freshly passed feces. That being said, I'd still report this as hookworm ova..."  

Lastly, Sarah astutely commented on my Facebook ParasiteWonders page that this was "Probably hookworm, but I feel like this is a trick problem and I wouldn’t be discounting Oesophagostomum—they’re also pretty barrel shaped which is suspicious for Oes."  I love the healthy skepticism! I have certainly been known to post 'trick' cases. The parasite that Sarah mentioned, Oesophagostomum, is a nematode in the family Strongylidae that is found in tropical settings across several continents. Most human cases are found in Togo and Ghana and are due to O. bifurcum. However, cases have also been reported from Ethiopia where this patient was from. The eggs of Oesophagostomum are found in stool and are indistinguishable from those of the human hookworms; therefore we need to consider Oesophagostomum in the differential diagnosis. Often a presumptive diagnosis of Oesophagostum sp. infection can be made on clinical grounds, as infected patients usually present with nodular intestinal/abdominal disease caused by developing larvae in the intestinal wall. Another feature that is helpful in the differential diagnosis is that the eggs of O. bifurcum are usually at a later stage of cleavage than hookworm species when shed in stool, so seeing an egg with only 4 blastomeres would be unlikely. 

Monday, March 1, 2021

Case of the Week 628

 This week's case is from Idzi Potters and the Institute of Tropical Medicine, Antwerp. It looks somewhat similar to last week's case, but it is very different! 

The following objects were seen in a stool specimen from a middle-aged male with recent travel to Senegal.