Monday, April 12, 2021

Case of the Week 634

 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)


Monday, April 5, 2021

Case of the Week 633

 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?

Sunday, April 4, 2021

Answer to Case 633

 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!

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.


Sunday, February 28, 2021

Answer to Case 628

 Answer to the Parasite Case of the Week 628: Parasitic plant nematode eggs (e.g., Heterodera sp., Meloidogyne sp., Meloidogyne sp.); not a human parasite. 

Sarah Sapp was the first to get this one (nice job Sarah!). She commented on our Creepy Dreadful Wonderful Facebook page that "I suspect this could be spurious passage of Meloidogyne (root knot nematode) eggs—size looks consistent, and also the very rounded ends with a concave broad side."  

While we didn't identify the actual genus of the nematode, we can say with confidence that this is a plant nematode based on the larger size and distinctive shape:

This case is a great reminder that nematodes are all around us - free-living, or parasitizing living things besides humans - and they can occasionally be ingested by us and be seen in human stool specimens. This adds to our challenge of differentiating them and their eggs from similar-appearing human parasitic nematodes that may be found in human stool. 

In this case, the primary differential would be the eggs of the human hookworms, as well as those of Strongyloides spp., and Trichostrongylus. These eggs can be excluded in this case by their smaller size and ovoid shape. Also in the differential are mite eggs, as shown in our case from last week.  

Thanks to Idzi Potters for another fantastic case!

Monday, February 22, 2021

Case of the Week 627

This week's interesting case was donated by Dr. Karine Thievierge and Alexandra. The following structures were seen in a stool specimen. They measure between 110 - 140 micrometers in length, by 75 - 90 micrometers in width.  Identification?

Sunday, February 21, 2021

Answer to Case 627

 Answer to the Parasite Case of the Week 627: Mite eggs; finding is not of medical concern

Mites and their eggs may occasionally be found in human stool specimens, given that mites are all around us - in dust, on our skin, and in our food! (check out my previous case of the week on Cheese Mites). Although mite eggs resemble those of some human parasites (e.g., the human hookworms), they are usually larger, and there is often evidence of an immature mite inside, as seen in this case:

Here are a couple of images from Dr. Jon Rosenblatt, my predecessor at Mayo Clinic. They show 2 larval mites, including one escaping from an egg. 

Live, moving, mites can occasionally be seen in direct wet preps of fresh stool - a somewhat disconcerting but insignificant finding. We don't report them when seen as it would just cause confusion for the ordering provider and patient!

Monday, February 15, 2021

Case of the Week 626

 This week's post is from my own collection - A Giemsa-stained preparation of vaginal secretions from a woman with dyspareunia. The objects measure approximately 15-20 micrometers in maximum dimension. 


On a related topic, I had the privilege of recording a podcast with Dennis Strenk, the founder and voice of the People of Pathology Podcast. You can listen to our podcast here:






Sunday, February 14, 2021

Answer to Case 626

 Answer to the Parasite Case of the Week 626: Trichomonas vaginalis. The images from this case show the classic morphology of this organism. Here are some of these key diagnostic features:

Although T. vaginalis can be seen in vaginal secretions, male urethral secretions, and in urine, the most sensitive detection method is a nucleic acid amplification test (NAAT). This is what we use in my laboratory. Importantly, the NAAT we use does not cross-react with the other trichomonads found in the oral cavity and intestine. 

As Sam mentioned, "Treatment with metronidazole would be appropriate. This would be of concern if the patient was pregnant as T. vaginalis can cause premature rupture of membranes, preterm birth, and decreased birth weights." T. vaginalis can also increase the risk of HIV transmission, so treatment is indicated even if the patient is asymptomatic.

Thanks to all who wrote in with comments!

Monday, February 8, 2021

Case of the Week 625

 This week's case was generously donated by Dr. Marijo Roiko, Dr. Shifteh Vahidi, and Ms. Marnie Larsen. Marnie noticed the unusual structure shown in the image below in a urine cytology specimen from an elderly male with a history of hematuria. The structure in the image was observed on PAP stain and was a solitary finding; it measures 125 x 75 µm.


What is this cool-looking object?

Sunday, February 7, 2021

Answer to Case 625

Answer to the Parasite Case of the Week 625: Not a parasite; rotifer

This fascinating "wheel animal" (from Latin rota "wheel" and -fer "bearing") has been seen a couple of times in the past on this blog. Check out our previous cases with great photos and videos:

Case 517 (unstained with video)

Case 304 (another Pap-stained case)

Here are some of the diagnostic features in this case:

Old one gives us a great description of the rotifer seen here: "Bdelloid rotifer with a retracted corona, large orange ovary, with 2 lateral germovitellaria with posterior stomach. Tail section appears to be visibly segmented with one of its toes visible at the terminal segment."

As I've noted in my previous posts, there is no clinical significance to this finding. Rotifers are found in environmental water sources, so it is likely that the organism entered the specimen through the collection process - possibly from a toilet using untreated well water.

Some of you suggested that this could be a miracidium of Schistosoma haematobium. While this is a good thought given the size and location, we can exclude this organism based on the overall shape of the organism, lack of circumferential cilia, and presence of a segmented foot (retracted, but still visible)..

Thanks again from our colleagues at Altru Health System for donating this fun case!

Monday, January 25, 2021

Case of the Week 624

 This week's case is a bit unusual in that it is an environmental sample (but the parasite has relevance to human health). The following were seen in a soil sample taken from a child's playground. They are approximately 80 micrometers in greatest dimension. Most likely identification?

Sunday, January 24, 2021

Answer to Case 624

 Answer to the Parasite Case of the Week 624: Toxocara sp. eggs. Note that one is fully embryonated and contains an L3 larva. These eggs are found in the feces of the definitive hosts: T. canis in canids and T. cati in felids. Based on the size, the eggs in this case of likely to be those of T. canis, which is slightly small than the eggs of T. cati (80-85 vs 65-75 microns respectively). Of note, these eggs are NOT found in human feces. However, they are a risk to humans if ingested, since eggs with larvae will hatch and can cause visceral larva migrans. That is why finding eggs in the soil of a child's playground is particularly concerning. 

The eggs can be identified by their thick outer shell with a pitted surface. It's a very striking appearance. 

You can read more about these fascinating zoonotic parasites on the U.S. Centers for Disease Control and Prevention (CDC) DPDx website. Toxocariasis is identified by the CDC as one of 5 Neglected Parasitic Infections in the United States, and is quite prevalent in many places worldwide. 

Tuesday, January 19, 2021

Case of the Week 623

 The following objects were seen on a peripheral blood film from a patient with chronic, worsening swelling in his groin over the past 5 years. He is from Central Africa. The stain is the Delafield's hematoxylin. Diagnosis? 

Sunday, January 17, 2021

Answer to Case 623

 Answer to Parasite Case of the Week 623: Wuchereria bancrofti microfilariae

This case showed all of the classic features of W. bancrofti microfilariae, including the sheath which was nicely highlighted by the Delafield's hematoxylin stain. The sheath may not always be seen with routine Giemsa stain; when it is present, it often appears as a negatively-staining outline only. The Delafield's hematoxylin isn't routinely performed in the parasitology laboratory, but it is in all of the classic parasitology texts as an option for highlighting microfilariae sheaths. It's a beautiful stain!

Here are the features of interest:

  1. Presence of a sheath
  2. Nuclei do not go all the way to the tip (tip is Without nuclei in Wuchereria)
  3. Width of the microfilaria is about the same or greater than the surrounding WBCs on thin blood films. This is in contrast to Mansonella spp. which are more slender than the WBC diameter on thin films (important when a sheath is not seen).

Monday, January 11, 2021

Case of the Week 622

 This week's case was graciously donated by Dr. Kyle Rodino, one of our outstanding former Medical Microbiology fellows. The following specimen was submitted to the clinical microbiology laboratory in vodka (which deserves extra points for creativity). Identification?

Sunday, January 10, 2021

Answer to Case 622

 Answer to the Parasite Case of the Week 622: drunken Pediculus humanus capitis

There are pretty entertaining and interesting comments that I would encourage you to read if you are interested! Here are some of the key findings in this case:

Thanks again to Dr. Rodino for donating this interesting case.