This week's case is donated by Dr. Luis Fernando Solórzano Álava from Ecuador. The 'patient' is not a human, but rather an Ecuadorian snail. However, the parasite shown is indeed very pathogenic to humans and has a predilection for the central nervous system.
Answer: Angiostrongylus cantonensis, the rat lungworm
As many of you mentioned, the clues to the identification of this parasite are the characteristic morphology of the larvae, the host (snail), and the predilection of the parasite for the human central nervous system (CNS). A. cantonensis can infect snails and slugs, which if accidentally ingested, can lead to debilitating, even fatal, eosinophilic meningitis in humans when the immature worms migrate to the CNS and die. Human infection can also be acquired through ingestion of infected paratenic hosts such as crabs and fresh water shrimp, and may potentially be acquired through ingestion slug/snail slime containing L3 larvae on inadequately-washed vegetables.
Although this infection was first identified in Asia, it has spread throughout the Pacific basin, and is also found in parts of Africa, the Caribbean, and Ecuador. Florida Fan points out that the related organism, A. costaricensis, causes intestinal angiostrongyliasis, and is found in parts of South and Central America. Most cases of A. costaricensis infection are reported from Costa Rica
Here are some nicely-labelled images that Dr.
Solórzano Álava created for this case that demonstrate
the key morphologic features. I find the pointed tail to be especially
The patient is a frequent traveler who recently returned from Kenya where he participated in a game tracking excursion. He now presents with high fever, malaise and headache. The following were seen in a preparation of unfixed blood:
Answer: Trypanosoma brucei
This is most likely T. brucei rhodesiense based on:
The patient's recent travel to Eastern Africa (Kenya),
His participation in a game tracking excursion (classic history given that wild ungulates are the reservoir for this subspecies),
His rapid onset of symptoms, and
The very high (!) parasitemia
Be sure to check out the video which show the characteristic 'auger' like motility of the trypomastigotes (i.e. rotating along its long axis).
Thanks to everyone who wrote in with the excellent comments. A lot of good points were raised by all. Ali Mokbel mentioned that we can't exclusively rule out T. b. gambiense, given that the patient is a frequent traveler and may have been to West Africa. Idzi also reminded us that the trypomastigotes of T. brucei are indistinguishable from those of T.rangeli, a non-pathogenic New World trypanosome which can occasionally infect humans. Fortunately, we can tentatively rule out these other species/subspecies based on the very high parasitemia and patient's symptoms. If there was any question about the identification (e.g. based on the patient's travel history), sub-species determination using PCR could be performed.
Finally, LS reminded us of the importance of determining whether the patient had central nervous system involvement since that would change the therapy. If suspected, a lumbar puncture could be performed to look for trypomastigotes.
For our students of parasitology, the following contains some general information about trypomastigotes, the most trypanosome stage seen in peripheral blood. Trypomastigotes are extracellular, unlike Plasmodium parasites, and may be seen 'swimming' between the red blood cells as in this case (check out Idzi's really cool video!). Although they have a somewhat 'worm-like' appearance, they are protozoa (not helminths), and can be easily differentiated from microfilariae by their small size (14 to 33 micrometers in length). They have a kinetoplast at their posterior end (arrows in image below) and a centrally located nucleus. A flagellum arises from the basal body (associated with the kinetoplast) and travels along the long axis of the trypomastigote as an undulating membrane. It projects from the anterior end as a free flagellum (arrow head, below), and provides the characteristic 'auger-like' motility of the trypomastigote.
Note that the flagellum is at the anterior end of the trypomastigote, and not the posterior as many would expect!
The size of the kinetoplast is very useful for differentiating the trypomastigotes of T. brucei/T. rangeli from those of T. cruzi. As you can see from the image below, the kinetoplast of T. cruzi is much larger:
Answer: Probable anisakid (Anisakis sp., Pseudoterranova sp., or Contracaeceum sp.)
There was a lot of great discussion on this case! While we can't definitively rule out a migratory immature Ascaris lumbricoides (crawling up from its usual intestinal location), the size of the worm, morphology, and patient history are most consistent with this being an anisakid larva. Anisakiasis occurs in humans following consumption of undercooked fish or seafood containing coiled anisakid larvae. The larvae cannot mature in humans but still have the potential to cause significant problems for their unintended human host. In the 'best case scenario', the larva dies and is passed in stool. If seen by the patient, it may be submitted to the laboratory for identification. A less optimal scenario is what was seen in this case where the live larvae crawls up the esophagus and is 'coughed up' or expelled out of the mouth. While no doubt disturbing, this is still better than the alternative, in which the larva burrows into the gastric or intestinal mucosa, causing significant pain for the host. If the larva is not immediately removed, the patient may experience symptoms for an extended period of time until the larva dies and is absorbed by the host. Rarely, the larva will penetrate the wall of the stomach or intestine and enter the peritoneal cavity, wreaking further havoc. A final, but equally important, complication of exposure to anisakid larvae is development of an allergy to anisakid proteins. This can occur regardless of whether the larva is alive or dead. Sensitized individuals must avoid anisakid-infected fish or risk experiencing serious allergic, or even anaphylactic, reactions, upon re-exposure.
Anisakid larvae can be identified by a few features: they are ~3 cm in length, have 3 fleshy lips just like A. lumbricoides, and also have a very small 'boring' tooth on the anterior end (which can be very difficult to see). Some species also have a posterior spicule called a mucron which is easier to identify. Ascaris doesn't have a boring tooth or posterior mucron, so these are helpful features when seen. Unfortunately the posterior end was damaged during removal so we weren't able to examine it.
What I found to be very interesting about this case was the history of hives, suggesting an allergic reaction to the larva. The time frame of symptoms was also interesting - the patient experienced hives for ~ 1 month before expelling the worm, which indicates that either the larva was present all of that time without causing any gastrointestinal symptoms, or the patient had ongoing exposure to anisakids through his diet. I'd be curious to know - have any of my readers run into a similar case? This is actually the second case I've seen where the patient had been symptomatic for several weeks after presumed exposure and before expelling the larva. This leads me to think that some larva can exist in the host for weeks without burrowing into the gut lining. Please let me know what your experience has been!
Answer: Loa loa
This great case by Dr. Green shows a gravid female worm with characteristic irregularly-spaced elevations on the cuticle called "bosses". Identification of the bosses allows the adult worm to be differentiated from the similar-appearing adults of many Dirofilaria spp. which have cuticular ridges rather than bosses. William Sears also commented on some of the other characteristic features which aid in identification: a straight buccal canal and muscular esophagus.
Several of you correctly identified the additional test that would be useful for confirming our diagnosis: examination of Giemsa-stained peripheral blood films (collected between 10am and noon) to look for characteristic sheathed microfilariae. This was done, and microfilariae were readily identified:
Note the evidence of a sheath (seen as a negative outline in this case) and nuclei that go to the tip of the tail, consistent with Loa loa microfilariae.
Happy Valentine's Day! Here is a special photo taken by Emily Fernholz, my awesome education specialist. These 2 little worms were found in a concentrated stool specimen and measure approximately 250 micrometers long. Identification?
Answer: Strongyloides stercoralis rhabditiform larvae
As noted by Florida Fan and Sugar Magnolia, these 2 larvae are "intertwined in romantic interlude" - "performing a romantic ballet". Perfect for Valentine's day!
The identification can easily be made by the size of these nematodes, their short buccal cavities (arrows in image below), and the genital primordium (less easily appreciated here).
The patient is a 65 year old Spanish woman who brought 3 worm-like structures to her physician. She had expelled the structures 30 minutes prior to presentation, and one was noted to still be moving. She reports no travel outside of Europe.
As mentioned by Luis, Florida Fan, Atiya, and Sugar Magnolia, these proglottids can be differentiated by other large tapeworms by the size and shape of the proglottids, and the presence of more than 12 uterine branches arising from the central uterine canal/stem:
Remember when counting uterine branches to only count them as they come off the central stem (primary branches), and only on ONE side (not both)!
As some readers mentioned, the proglottids of Taenia saginata are morphologically indistinguishable from those of T. asiatica; however, the patient's lack of travel outside of Europe makes infection with this latter parasite unlikely. Thanks again to Idzi Potters and the Institute of Tropical Medicine, Antwerp, for this interesting case!
The identification of this roundworm is based on its large size, tapered head and characteristic trilobate (3) "lips":
This worm can be further identified as a female based on its straight rather than coiled tail. Ali also astutely noted the presence of a "vulvar waist" - a narrowing at the junction on the anterior and middle thirds of the body, which also indicates that it is a female. Kamran was unable to express any eggs out of the worm; if found, the presence of eggs would also have confirmed the female gender. The size (30 cm) falls within the range of both male and female worms and therefore unfortunately cannot be used to identify the gender in this case.
Thanks to all of my readers for the excellent comments!
This week's case was generously donated by our long time contributor, Florida Fan. The following were noted in the stool of a apparently healthy man with no known travel history. The eosin wet mounts were photographed using the 40x objective, while the trichrome-stained slides were photographed using 100x. We don't make eosin saline mounts in my laboratory anymore; I had forgotten how pretty they can be.
Answer: Entamoeba coli trophozoites and cysts. Also present is a trophozoite of Dientamoeba fragilis.
This case from Florida Fan nicely shows the diagnostic features of E. coli, including the large size and >4 nuclei in the mature cyst stage:
Again, the colors of the trichrome and eosin saline mounts are beautiful.
As I mentioned above, there was also a D. fragilis trophozoite present. Because of its small size and indistinct chromatin features, this organism is significantly more difficult to identify. Here is the current case (bottom, left), as well as an idealized photo from my own collection (bottom, right). Note that the trophozoites have 1 to 2 nuclei with a 'fragmented' or 'fractured' chromatin pattern. The chromatin may also have a smudgy appearance.
Thanks again to Florida Fan for donating this case!
This week's case was generously donated by Dr. Piryanka Uprety and the excellent Clinical Microbiology and Hematology Laboratories at the University of Pennsylvania. The following structures were initially observed by a hematology fellow in a wet mount (40X) from a BAL specimen. Photographs and videos are courtesy of Joyce Richardson, Vivian Whitener, and Darrin Jengehino from the Hematology Laboratory.
Wet preparation of the BAL fluid with iodine showed the following:
Answer: ciliated respiratory epithelial cells. These are a common parasite mimic, especially when seen in unfixed wet preparations, since the cilia remain motility for quite some time after being exfoliated from the respiratory mucosa. It is important to note that these are NOT parasites. Unfortunately there are several reports where these are misidentified as Lophomonas blattarum; however, L blattarum is a parasite found in various arthropods and is NOT thought to be a human parasite.
You can easily identify ciliated epithelial cells by their small size and characteristic shape. Note that the cilia are present in a dense band at the apical surface:
You can really appreciate the columnar shape of the cells in this case.
It can be even more challenging when the ciliary tufts become detached (called detached ciliary tufts/DCTs or ciliocytophthoria). I've featured this multiple times on my blog in the past and have described how to differentiate ciliated host cells from other microorganisms. Check out these past posts for more information:
Answer: Adult Toxocara cati; the presence of this adult worm represents either environmental contamination (e.g. from an infected cat) or spurious passage by the child.
This case generated an excellent, entertaining, and somewhat disturbing (!) discussion. As many of you correctly noted, this is an adult Toxocara species. It has a similar appearance to Ascaris lumbricoides, but can be differentiated by the presence of the pronounced short, wide cervical alae:
The shape of the alae allow it to be differentiated from other Toxocara species. Note that the alae narrow towards that anterior end, giving the appearance of an arrow (image by my excellent parasitology technologist, Emily Fernholz).
Humans are not a definitive host, but can acquire infection with the larval form of the worm when accidentally ingesting eggs in contaminated soil or infected paratenic hosts. The larvae cannot mature in humans, but can migrate throughout the body causing a potentially serious condition called visceral larva migrans.
So how did this adult worm end up in a human host? Well, we can't really say for sure that it actually was IN this patient since it was noted outside of the body during bathing. Therefore it could have been expelled by family cat and simply ended up in the bathtub.
Alternatively, it could be that the child had ingested an adult or immature worm from the environment (the term kitty spaghetti will stick with me forever! See the comments for more information) and it had passed through her intestinal tract and was expelled intact. Authors from the US CDC published a interesting series of cases like this in 1998. You can read the article HERE.
Regardless of the scenario, it is clear that there is an infected household cat that needs to be treated. As I mentioned above, eggs that are shed from infected cats can mature in the environment and pose an infectious risk to humans (i.e. visceral larva migrans).
Happy New Year! This week's case is by Idzi Potters and the Institute of Tropical Medicine Antwerp. The following were seen in an unfixed stool specimen at 400X original magnification. (Hint: maximize the size of the video for best viewing). Identification?
Every week I will post a new Case, along with the answer to the previous case. Please feel free to write in with your answers, comments, and questions. Also check out my image archive website at http://parasitewonders.com. Enjoy!
The Fine Print: Please note that all opinions expressed here are mine and not my employer. Information provided here is for educational purposes only. It is not intended as and does not substitute for medical advice. I do not accept medical consults from patients.