Tuesday, November 24, 2020
Monday, November 23, 2020
Answer to Parasite Case of the Week 615: Strongyloides stercoralis rhabditiform larva, eggs, and adults. Note the eggs inside and out of the beautifully-photographed adult worms by William Sears. As you may know, the parasitic females reproduce without the males using a process called parthenogenesis.
This 'composite' case didn't have any accompanying clinical information, but a classic scenario would be hyperinfection infection in a profoundly-immunocompromised patient.
It's important to note that it's not possible to definitely make the diagnosis on the images from this case alone, especially since the buccal cavity of the rhabditiform larva is not visible. You all did an excellent job coming up with the differential diagnosis. I'd highly recommend reading all of the comments on the blog (or on Twitter @Parasitegal) to see great descriptions and stories.
Here are the options of what this case could be:
1. S. stercoralis hyperinfection (For another example, see the previous Case of the Week 469 and the accompanying Answer). It's important to realize that embryonated eggs and adults may rarely be seen in stool specimens in heavy infections. Here's a great photo from Case 469 to demonstrate the size difference between adults and rhabditiform larvae:
2. Strongyloides fuelleborni infection, in which eggs containing rhabditiform larvae are found in stool. In this case, we wouldn't have expected to see adult worms in the stool. See the previous Case of the Week 593 donated by Idzi Potters for more information.
3. Hookworm infection, in which unfixed stool was allowed to sit for some time prior to examination, allowing eggs to embryonate and hatch. Great thought! This doesn't account for the adults in stool, however, which would not be expected in hookworm infection.
4. Mixed hookworm and Strongyloides infection. Allowing the eggs to hatch (e.g., using the Harada-Mori culture technique) and then examining the rhabditiform larvae would allow for differentiation of hookworm and Strongyloides. Alternatively, molecular testing at a specialized research laboratory could also help to sort this out.
5. Spurious passage of a soil/plant nematode.
Wishing you all a very happy and safe Thanksgiving day!
Monday, November 9, 2020
Sunday, November 8, 2020
Answer to Parasite Case of the Week 614: Cystic echinococcosis caused by a member of the Echincoccus granulosus complex.
As Clinton White nicely explained in the case comments, "We now know that human infection is caused by several species and genotypes within what was once thought of as a single species." The species implicated in human disease are E. granulosus (genotypes G1-G3), E. ortleppi (G5), and E. canadensis (G6-G8, G10). Most of these have a wide geographic distribution, including regions of North America, Europe, Asia, and the Middle East. In South America, 2 additional species cause neotropical cystic echinococcosis, E. vogeli and E. oligarthra. Echinococcus multilocularis causes a very different form of disease called alveolar echinococcosis. Unlike the species that cause cystic echinococcosis, E. multilocularis expands throughout the tissue in an infiltrative pattern, much like a malignancy, forming microscopic and macroscopic cysts without a well-defined surrounding laminated layer. Protoscolices are rarely seen in human E. multilocularis infections.
Molecular analysis, as well as correlation with the radiologic findings and the patient's exposure/travel history are used to determine the causative species. In this case, the patient had not travelled outside of North America and had a single pulmonary cyst, consistent with a diagnosis of simple cystic echinococcus (CE; CE1 on the World Health Organization classification scale).
This case shows characteristic protoscolices and free hooklets of E. granulosus complex. The hooklets are especially beautiful with Wheatley's trichrome staining, in which they have a somewhat iridescent appearance:
Monday, November 2, 2020
This week's case is something that we only occasionally get to see in my laboratory - kindly donated by Dr. Ryan Relich. The patient presented with a past history of malaria, and she had not completed her full course of anti-malarial therapy. Therefore, her physician ordered peripheral blood films which revealed the following. Travel history is unknown at this time. It's a little hard to tell from the images, but the nuclei go to the tip of the tail.
Sunday, November 1, 2020
Answer to the Parasite Case of the Week 613: Loa loa microfilariae
Although some readers suggested that these structures could be artifacts (e.g. fibers that got onto the blood films), we can tell that these are microfilariae by the size, shape and presence of nuclei within the worms. The tail nuclei weren't entirely visible in the images, so I gave the hint that the nuclei go all the way to the tip of the tail. That leaves us with just 2 microfilariae to consider: Loa loa and Mansonella perstans.
As nicely described by Idzi, the size of the microfilariae is the most important feature for differentiating these two: "Mansonella is ruled out by its thickness. A nice trick is to compare the diameter of the microfilaria to the nuclei of the white blood cells. Mansonella would be half of the WBC nuclei’s diameter while the others are more or less the same." Loa loa microfilariae are also sheathed, whereas those of M. perstans are not. Unfortunately, it is not always possible to see the sheath of Loa loa (as well as Wuchereria bancrofti) on Giemsa-stained blood films.
Florida Fan offered up a very nice example of where the sheath is visible:
You can see the sheath extend from the tip of the tail, up towards the "20" of the scale bar.
If you have your heart set on seeing the sheath, another neat trick you can use it to stain your blood films with hematoxylin. The Delafield's hematoxylin protocol is usually recommended for this purpose, but the routine hematoxylin and eosin (H&E) stain in your anatomic pathology lab will also do in a pinch. Here are some microfilariae images from this case using H&E staining - what a beautiful sheath!
Thanks again to Dr. Ryan Relich (a.k.a. MicrobeMan) for donating this case.
Monday, October 26, 2020
Sunday, October 25, 2020
Answer to Parasite Case of the Week 612: fly larva (maggot), Lucilia species. By using a pictorial key from the CDC website, I would say that this is most likely Lucilia (Phaenicia) sericata, the common green bottle fly. The presence of three spiracular slits indicates that this is a third instar larva (second instar larvae each have 2 slits).
Congratulations to the many viewers who wrote in with the correct answer! As nicely explained by Idzi, Jeff, Florida Fan and Kosta, the appearance of the spiracular plate (straight slits, complete peritreme), and lack of an accessory oral sclerite points to this being Lucilia rather than Calliphora sp.
1. It is a cause of facultative myiasis in humans and animals.
2. It feeds on carrion, and is commonly used in forensic entomology to estimate the time of death.
3. It is used for maggot therapy in humans, as the larvae will effectively feed on necrotic tissue and thus aid in wound debridement. Maggots are specially raised for this purpose and disinfected prior to use. You can see some 2nd instar Medical Maggots (TM) that were sold for human maggot therapy HERE.
Florida Fan commented on how challenging it can be to get a picture perfect image of the spiracular plates. Emily and I learned at the London School of Hygiene and Tropical Medicine how to carefully prepare fly larvae for mounting to create truly beautiful preparations. However, for routine clinical use, we also like to play around with foam and applicator sticks to position the larva just right under the camera.
Monday, October 19, 2020
Sunday, October 18, 2020
Answer to Parasite Case of the Week 611: Female crab louse, Pthirus pubis, with an egg. She's a mom to be!
Florida Fan pointed out that we would be able to tell that this was a female louse, even if she wasn't gravid, due to the somewhat flattened, indented posterior (vs. the rounded posterior of the male).