Dear readers, I will soon be posting my 500th Case. Hooray!! To celebrate, I would like to recognize the creativity of my readers by displaying a photograph of your parasite-related artwork on my blog. I will then put the names of all of the individuals who submitted a photo of their art in a hat and pick 3 names to receive a special parasite prize ☺ If you would like to send me a photo that I can post on my blog on July 2nd, please send it to email@example.com
Now for this week's case - some beautiful eggs from my lab (images and video by Heather Rose):
This week's case was generously donated by Florida Fan. The following bug were submitted by the physician of a 69-year-old woman. No further history is available. As Florida Fan says, "Here comes the summer, and with it comes the bugs."
Answer: Cimex species; bed bug
As Blaine mentioned: "B&B Bugs is back! Beautiful brown biting, blood-sucking bed bug! Boo-yeah!" William mentioned that the pronotal hairs are not long enough to be a bat bug - an important consideration since bat bugs can be found near human dwellings and may bite humans when their preferred (bat) host is not available.
The patient is a 65-year-old owner of a camel farm who presents to his primary care provider for a yearly check-up. As he has mild intestinal complaints, he submits a fecal sample to be checked for parasites. The following structures were observed, and measure approximately 85 x 45 microns. Diagnosis please?
Concentrated wet preparation, 400x
Concentrated wet preparation, 400x with Lugol's iodine
Answer: Trichostrongylus sp. egg
Congratulations to everyone who wrote in with the correct answer. Although this egg looks like those of the hookworms, Oesophagostomum spp., Ternidens spp., and Strongyloides stercoralis (latter only rarely seen in stool), the larger size (85 micrometers long) and tapered end points us towards Trichostrongylus.
This diagnosis is also supported by the history of camel exposure, as Trichostrongylus is primarily a parasite of ruminants. As Blaine mentioned, I should have posted this case on a Wednesday for 'hump' day!
William Sears also mentioned that the presence of eggs with well-developed larva indicates that the specimen likely sat for some time before being examined since the eggs are passed in human stool in an unembryonated state. Thanks again to Idzi Potters for donating this fascinating case.
This week's case was donated by Dr. Kamran Kadkhoda. It's a 'real life' case that I thought provided a fun challenge. The specimen was obtained from a 5 year old boy from Canada and submitted to the laboratory for identification. What do you all think?
Answer: Ixodes species tick (fragment), unengorged female
As Blaine, Idzi, Sheldon, Florida Fan, Richard, Agnes, and William nicely described, we can easily identify this tick fragment as an Ixodes species by its characteristic 'U-shaped' anal groove. Lack of festoons also supports the identification. One of our tick experts, Ellen, mentioned that the color is a good feature for determining sex, since female Ixodes are orange-brown while males are black and nymphs are transparent charcoal-grayish. Color can also be helpful for determining the degree of engorgement since adult females will become grayish-white once becoming engorged due to growth of new opisthosoma tissue. Thanks for the great description Ellen!
The tick is most likely I. scapularis, but could also be I. pacificus if it was from Western Canada. Dr. Kadkhoda (who donated this case) is in Manitoba, so I. scapularis would be most likely. Given the partial nature of this tick, we also need to consider other human-biting Ixodes species such as I. muris.
Answer: Malaria due to Plasmodium falciparum; >20% parasitemia
There were lots of great suggestions for what the lab should do after making this identification. The step of primary importance is to urgently contact the clinical team to relay the result and ensure they understand the importance of the diagnosis. In my laboratory we treat all malaria diagnoses as critical results. In this case, the causative agent (P. falciparum) and the high parasitemia (>2%) make this call even more urgent, since the patient is at very high risk of death from his infection and requires immediate treatment.
In addition to antimalarial treatment (e.g. IV quinidine or artesunate), red blood cell exchange may also be performed for patients with >10 % parasitemia. While the United States Centers for Disease Control and Prevention (CDC) no longer recommends red cell exchange for severe malaria, many other groups such as the American Society for Apheresis (ASA) feel that it is still warranted in life-threatening infections such as this one. You can read the arguments for red blood cell exchange for malaria with >10% parasitemia here:
The mother of a 5 year-old
Belgian patient brought in a small worm-like structure (measuring 12 mm in length) along with a fecal sample. Microscopic examination of the worm-like structure using low power magnification revealed the following:
A direct wet
mount was made from the stool sample. The structures that are found in the wet
mount are shown in following image and videoclips.
Check out these cool videos (you may need to press play twice)
Answer: Enterobius vermicularis adult female and eggs (containing viable larvae). I hope you all got to see the beautiful video of 'baby's first steps' (or wriggles?) that Idzi provided showing a larva hatching from an egg.
The diagnostic features include prominent cervical alae, bulbous esophagus, pointed 'pin-like' tail, and "D" shaped eggs, with flattening on one side.
As Florida Fan mentioned, Blaine did a fabulous job replicating these eggs in his Halloween costume last year.
Answer: Histoplasma capsulatum
This small oval-shaped fungus has a very similar appearance to the amastigotes of Leishmania species (and Trypanosoma cruzi), as well as the tachyzoites of Toxoplasma gondii. It is therefore always in my differential of small intracellular objects when I am looking at blood smears, bone marrow aspirates and tissue sections. All of these objects measure 2 to 5 micrometers in greatest dimension and can be found within phagocytic cells. However, there are several key differentiating features that allow for a correct identification to be made:
1. Leishmania spp. amastigotes - have a single nucleus and rod-shaped kinetoplast. They are found within macrophages/monocytes.
2. T. cruzi amastigotes - are indistinguishable from Leishmania amastigotes but have a different tissue tropism (e.g. cardiac and smooth muscle cells) and associated clinical presentation.
3. Toxoplasma gondii tachyzoites - are arc-shaped (but can appear oval in tissue) and have a single nucleus with no kinetoplast. They can infect any nucleated cell.
4. Histoplasma capsulatum yeasts - are found within macrophages/monocytes and divide by narrow-based budding. As Sugar Magnolia mentioned, their cell wall does not take up many stains well (e.g. Giemsa, H&E), and therefore they appear to have a surrounding capsule (sometimes termed a pseudocapsule). This is where the species name, capsulatum, comes from. A silver fungal stain (e.g. Gomori methenamine silver) will stain all of the yeast including its cell wall. In contrast, amastigotes and tachyzoites do NOT stain with GMS.
It's important to note that other yeasts such as Penicillium marneffei and Cryptococcus neoformans will also stain with silver fungal stains and may have a similar appearance to H. capsulatum in peripheral blood films. They can be differentiated through a careful examination of several morphologic features; Cryptococcus neoformans has a true capsule, unlike H. capsulatum, and exhibits more size variability, whereas Penicillium marneffei divides by formation of transverse septations rather than budding.
Whew! That was a long explanation. Kudos to my excellent parasitology technologists who correctly detected and identified the H. capsulatum on the malaria smears. I later found out that the patient was severely immunocompromised with AIDS - a common scenario for histoplasmosis detected on peripheral blood films.
This week's case is courtesy of Dr. Delgado and the Yale Pathology department. The patient is young adult male with extensive travel throughout Europe, Central America and Africa, who presented fever, drenching night sweats, extreme fatigue, cervical lymphadenopathy and splenomegaly. CBC showed pancytopenia. The following are from the H&E-stained bone marrow biopsy and Giemsa-stained aspirate.
Answer: Visceral leishmaniasis due to Leishmania species (Leishmania donovani complex or L. tropica). As noted by Brady Page, Anon, Florida Fan, William Sears, and Daniel Skipper, the diagnosis can be easily secured by identifying the amastigotes within mononuclear phagocytes. Each amastigote has a small eccentric nucleus and rod-shaped kinetoplast, giving the so-called "dot-dash" pattern (thank you @JClinMicro)
And thank you to our poet, Blaine, who gave us the following:
This week's case is generously donated by Florida Fan. The following object was submitted to the laboratory for identification. It had been retrieved during colonoscopy from the cecum of a 40-year-old man.
Answer: Female Trichuris sp.
The most likely etiology is T. trichiura. However, as several readers mentioned, human infection with T. vulpis has rarely been reported and the adult worm has a similar appearance. The two worms are differentiated primarily by their eggs, with T. vulpis eggs being nearly twice as large as T. trichiura eggs. The only eggs we see in this case are immature and intrauterine; therefore it is not possible to use the eggs to help us differentiate the two worms.
Here are some of the key diagnostic features of this case:
Note that the head is at the slender end (all the better for embedding into the large bowel mucosa), while the larger end (containing the uterus and eggs) hangs free in the bowel lumen. We can tell that this is a female worm because of the eggs in the uterus (below) and because the tail is not coiled like a male's tail would be.
Answer: Entamoeba coli or 'uniamoeba'!
While this case shows a beautiful trophozoite 'unicorn' for national unicorn day, it has an atypically-large karyosome which makes it challenging to identify it as E. coli. I therefore added some additional trophozoite photos from this case. Note the smaller, eccentric karyosome and clearly clumped peripheral chromatin seen in the following trophs:
As Idzi pointed out, this one looks like a dog's head!
The cysts were clearly consistent with E. coli, containing >4 nuclei (8 in the mature cyst).
Answer: Taenia sp.
Molecular testing showed this to be Taenia saginata.
There was a lot of great discussion regarding the differential on this case. Some of the key features were as follows:
1. Large size - although not given, you can see that this is a large tapeworm that fills the Petri dish. Even if this was a small Petri dish, the size would be most consistent with Taenia spp., Diphyllobothrium spp., and possibly Hymenolepis diminuta.
2. Size/shape of proglottids - this is one area where the ID gets tricky. Mature proglottids of H. diminuta and Diphyllobothrium are wider than they are long, whereas mature proglottids of Taenia spp. are longer than they are wide. The caveat is that immature proglottids of Taenia (as seen in this case) are also wider than they are long. Thus all 3 of these worms are in the differential. However, the proglottids of H. diminuta are very short and not like the ones shown in this case. Therefore, this diagnosis is less likely, leaving us with Diphyllobothrium and Taenia species as considerations.
3. Internal proglottid structures - this is a very helpful feature of this case since an internal 'rosette-shaped' uterus (consistent with Diphyllobothrium) is NOT present, but instead the opening to the lateral genital pore can be seen; the latter is consistent with this being a Taenia sp. proglottid.
Taenia sp. (this case); arrows show openings to lateral genital pores:
Diphyllobothrium sp. shown for comparison showing central rosette-structured uterus:
H. diminuta showing extremely short proglottids (from CDC DPDx):
4. Morphology of the eggs - another tricky factor here! This egg clearly contained a hooked-onchosphere, but it lacked the outer shell of Hymenolepis and the outer striated wall of Taenia spp. As mentioned above, this was a Taenia sp., and thus the lack of the thick striated outer shell can be attributed to the immature state of the egg (matching the immature proglottids).
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.