Monday, December 10, 2018

Case of the Week 522

This week's case features a whole slide image (WSI) of an H&E-stained section from a bladder resection. You can access the WSI HERE. Like the other WSIs that I've features on my blog, you don't need any special software or a log-in username to access the image. You can easily use the track ball on your mouse to zoom in and out. If using a smart phone or tablet, you can pinch in or out to zoom. Enjoy! (P.S. there are 2 things of interest on this slide).

Sunday, December 9, 2018

Answer to Case 522

Answer to Case 522Schistosoma haematobium eggs and adults.

Kudos to those of you who saw both the eggs and the adults! I realize that many parasitologists are not used to seeing formalin-fixed paraffin-embedded tissue sections, so here is an overview of the tissue and the primary findings:
This full-thickness section of bladder wall shows a very inflamed mucosa (epithelium and lamina propria) with numerous Schistosoma eggs. Most pathologists would immediately pick out the eggs - each with a thin outer shell and internal miracidium.
However, what many may not have noticed was that the culprits of this disease were also in the picture! Adult male and female schistosomes were residing within the bladder venules and can be seen in this section. As Old One mentioned, "The embrace (thanks eob) of the female by the male is unique to the "Schistos" for a couple reasons. Schistosomes derives from Greek meaning split of cleft body. This particular cleft is a split between male and female reproductive organs, making it dioecious (separate sexes) where other flukes are monoecious (both sexes in one individual). The small size of female to male is the second unique feature. This allows the female to break the embrace and swim down the smaller capillaries to deposit its eggs closer to the mucosal surface than if it were in a bulkier monoecious form, thereby being closer to the external environment. Improving the survival of the egg." Fascinating biology! I was told by one of my instructors years ago that the female usually came back to the same male after her egg-laying, but if she encountered another available male on her way back, she may stay with him instead (!)

Here are some cross-sections of our schisto couple - the male forming the outer part of the 'embrace' and the female being on the inside. Another one of my microbiology instructors likened this relationship to a hot dog and a bun. The male is the bun and the female is the hot dog.
The black pigment within the female is hemozoin formed through breakdown of the ingested host hemoglobin. This is the only parasite other than Plasmodium to form hemazoin pigment in humans. Nine years ago I posted a CASE of the male and female worms together which may help you better visualize their configuration.

Monday, December 3, 2018

Case of the Week 521

This month's case from Idzi Potters and the Institute of Tropical Medicine, Antwerp, features a stool specimen from a traveler returning from Iran. No clinical data is available, nor any additional lab-results. The following photos show structures that were found in the patient’s stools. The average size of these objects is 42 x 25 µm. Click on the images to enlarge.

What is the diagnosis (& possible clinical relevance)?

Sunday, December 2, 2018

Answer to Case 521

Answer: Dicrocoelium dendricitum eggs

This is relatively rare find in human stool specimens. The eggs are small (35-45 µm long by 20-30 µm wide), thick-walled, and often brown due to bile staining. They are shed in a fully embryonated state, with the embryo often easily seen within the egg (these look like a skull to me!)
D. dendricitum is such a fascinating parasite. Its life cycle typically involves as ruminant, a snail and an ant. The whole life cycle is nicely illustrated by the CDC DPDx group HERE. Here is the accompanying text: 
Ruminants are the usual definitive hosts for Dicrocoelium dendricitum, although other herbivorous animals, carnivores, and humans can serve as definitive hosts. Embryonated eggs are shed in feces. The eggs are ingested by a snail. Many species of snail may serve as the first intermediate host, including Zebrina spp. and Cionella spp. When the miracidia hatch, they migrate through the gut wall and settle into the adjacent vascular connective tissue, where they become mother sporocysts. The sporocysts migrate to the digestive gland where they give rise to several daughter sporocysts. Inside each daughter sporocyst, cercariae are produced. The cercariae migrate to the respiration chamber where they are shed in slime ball from the snail. After a slime ball is ingested by an ant, the cercariae become free in the intestine and migrate to the hemocoel where they become metacercariae. Many ants may serve as the second intermediate host, especially members of the genus, Formica. After an ant is eaten by the definitive host, the metacercariae excyst in the small intestine. The worms migrate to the bile duct where they mature into adults. Humans can serve as definitive hosts after accidentally ingesting infected ants.

What this nice narrative does not mention are the following fun facts:
1. While in the ant intermediate host, the parasite takes control of the ant's nervous system and controls its actions. It directs the ant to climb to the top of a blade of grass every night and clamp down tightly to the blade with its mandibles. At dawn, the ant goes back to its normal activity in its colony. The recurs night after night, with the poor parasitized ant residing on the blade of grass until it is eaten by the grazing definitive host! What a clever way for a parasite to ensure the continuation of its own life cycle. This story reminds me of the effect that Toxoplasma gondii has on its rodent host (a story for another day).
2. As Old One reminded us, "D.d is beautiful critter. So flat you can clearly see all it's major organ systems without the benefit of stains. So thin it is commonly called the Lancet fluke. These dimensions allow D.d to dwell within the biliary ducts where they can allow normal bile flow in small numbers or block the flow with greater numbers."  For this reason, the fluke is less likely to cause symptoms in its host.
3. When humans serve as the definitive host for D. dendricitum, eggs of the parasite may be seen in the stool. However, eggs may also be seen in the stool when humans inadvertently eat the infected liver of another definitive host such as a cow; in this scenario, the presence of eggs would be considered spurious passage or 'pseudo-parasitism'.

This brings us to the question that Idzi posed to us: What is the possible clinical relevance of finding these eggs in a human stool specimen? Luis and Nema both pointed out that it is necessary to rule out spurious egg passage due to ingestion of infected liver. To accomplish this Nema suggested collecting repeat stool specimens (instructing the patient not to eat any more liver!) If follow-up specimens are negative, then this would provide evidence that the patient was not actually parasitized. A related note is that liver ingestion is not common in many parts of the world, so getting a good dietary history (including possible ingestion of ants!) is very helpful.

I'll now leave you with a lovely story from Blaine:
So, there is this old story, or so I am told, about ants getting ready for the winter. They gathered up food stores all day, including slime balls produced by snails. Then along came a lazy grasshopper, which had spent the summer playing and not preparing for the winter. When the winter came, the grasshopper begged the ants for something to eat, even a slime ball!!! The ants refused. In the Spring, the ants had an insatiable urge to climb to the tops of blades of grass and ended up getting eaten by cattle and sheep! The grasshopper did not get eaten by the livestock. The moral of this story? Play all day and you are guaranteed not to become cow chow!