Monday, September 18, 2017

Case of the Week 460

This week's fun case was donated by Florida Fan. The following motile object was submitted along with an adult Ascaris lumbricoides. Specimen source is stool.

Wet prep:
 Trichrome stain:

Sunday, September 17, 2017

Answer to Case 460

Answer: Neobalantidium (formerly Balantidium) coli trophozoite

The identification can be made by recognizing the characteristic morphologic features and motility of the N. coli trophozoite. In this case, you can appreciate the circumferential cilia, large size (40 to 200 microns in greatest dimension) and macronucleus (partially seen in this case). The multiple globular structures within the trophozoite likely represent ingested microorganisms and cytoplasmic vacuoles.
The motility of N. coli is commonly described as 'boring', but as Mark Fox mentioned, this term is a bit misleading since there is nothing uninteresting about it! The alternative term, 'rotary', is perhaps a bit more illuminating.

Of note, several readers mentioned that N. coli is associated with pigs and therefore inquired if patient had any pig exposure. Unfortunately we don't have that information in this case. However, this raises the additional point that the patient was also infected with Ascaris and pigs can be also infected with this round worm. Therefore, the case for potential pig exposure is very intriguing!

For those of you that like (or care about) taxonomy, I should mention that Ascaris suum (the species attributed to pigs) is now thought to be the same species as the human parasite, A. lumbricoides. This assertion is based on the numerous morphologic and genetic similarities that have been described between the two (see "Are Ascaris lumbricoides and Ascaris suum a single species?" by Leles et al. HERE). If they are the same species, then the name A. lumbricoides takes precedence since it was described first (1758 vs. 1782). Isn't taxonomy fun?

Monday, September 4, 2017

Case of the Week 459

This week's case is a stool specimen from an elderly man from Kentucky. He reports no travel history outside of the United States. The patient presented with an approximate 50 pound unintentional weight loss over the past several months as well as diarrhea and abdominal cramping.

The following were seen on the stool concentrate (Images courtesy of our Clinical Microbiology Fellow, Dr. Alexandra Bryson):
(10x objective)

(40x objective)

Diagnosis? What forms are seen here?

Sunday, September 3, 2017

Answer to Case 459

Answer: Strongyloides stercoralis infection.

Seen here are numerous rhabditiform S. stercoralis larvae, some possible filariform larvae, and embryonated eggs with viable larvae within. This level of infection is consistent with Strongyloides hyperinfection and warrants a rapid call to the clinical team to alert them to the diagnosis.

There were a lot of great comments on this case. Florida Fan, Angelica Maria and Khalid Elfeel nicely discussed the presence of the short buccal cavity and genital primordium - keys feature for differentiating the rhabditiform (L1) larvae of S. stercoralis from the similar-appearing larvae of the hookworm. Shown below is a comparison of the buccal canals of Strongyloides and hookworm rhabditiform larvae (latter courtesy of the CDC DPDx).

Here is an another composite image of the readily-identifiable genital primordium in S. stercoralis rhabditiform larvae (the one in hookworm rhabditiform larvae is inconspicuous).

I should mention that the hookworm larvae come into the differential only when unfixed stool is allowed to sit for more than a day before being examined, thus allowing time for the eggs to mature and hatch. Only unembryonated hookworm eggs are seen in freshly-passed stool, and it takes 1-2 days for the eggs to mature and hatch.

In comparison, seeing S. stercoralis eggs in stool is quite unusual. This is because eggs of S. stercoralis are usually laid in the intestine and quickly hatch to release rhabditiform larvae. Florida Fan, Mark Fox and Sugar Magnolia raised the possibility that the presence of eggs indicates a very high level of infection, which I believe to be correct in this case.

Finally, Anon reminded us that Kentucky is endemic for strongyloidiasis and therefore something that should be considered in patients from this area - especially before starting any immunosuppressive therapy. Along these same lines, you may be interested to see this recent article of hookworm in the American south, published in The American Journal of Tropical Medicine and Hygiene. There is an interesting associated news commentary that you can read HERE. It's so sad to see the poor sanitary and living conditions that are still present in the United States.

Monday, August 28, 2017

Case of the Week 458

This week's fun photograph was donated by Dr. Graham Hickling.

The accompanying questions are:
1. What is the (top) arthropod shown here?
2. What is the name of the behavior it is displaying?

Sunday, August 27, 2017

Answer to Case 458

Answer: Questing Ixodes sp. nymph climbing on another arthropod (a weevil)

This tick is exhibiting a behavior called "questing" (from the Latin quaerere 'ask, seek'). This is a behavior of hard ticks (family Ixodidae) in which they crawl up vertical surfaces such as grass, sticks and leaves and extend their front legs in order to facilitate contact with a suitable host. This behavior is often stimulated when the tick senses heat or movement - signs that a host is nearby.

What was fun about this photo is that it shows that ticks don't really care what they crawl up in order to get to their host. In this case, the weevil was in the way and therefore was also scaled. This reminded me of the inspirational posters that we see everywhere these days, and so I decided to make my own inspirational meme:
Anon points out that this tick could also be 'catching a ride' on the weevil. That behavior is called "phoresy" - a non-parasitic association between 2 organisms in which one travels on the body of another.

Happy Labor Day weekend to all of my American and Canadian readers!

Monday, August 21, 2017

Case of the Week 457

This timely case is from Florida Fan which he entitled "A Beast with Many Faces" due to this parasite's varying appearance with different stains/preparations. The following images were all taken by Florida Fan except for "A" which was taken by Emily Fernholz.

Images are all shown at 1000X original magnification (each line on the scale bar represents 1 micron).

Here is the key (all from stool):
A - wet preparation
B - iodine-stained wet prep
C - Trichrome stain
D - Wright Giemsa
E - Modified acid fast
F - Modified safranin


Sunday, August 20, 2017

Answer to Case 457

Answer: Cyclospora cayetanensis oocysts

Thanks again to Florida Fan for providing these colorful images. Idzi Potters mentioned that C. cayetanensis oocysts also produce beautiful autofluorescence. Instructions for observing their autofluorescence can be found HERE) Below is an image that Florida Fan gave me a while back which nicely highlights this phenomenon (oocysts are denoted by arrows):
Examination for autofluorescencing oocysts can be a quick way to screen for C. cayetanensis in stool, keeping in mind that other objects (including many non-parasites) will also exhibit autofluorescence. The regular size and smooth round shape of the oocysts usually allow them to be easily identified. Alas, the fluorescence scope in my lab doesn't have the correct filters for observing autofluorescence, so this is not a technique that I can use.

Note that the oocysts of C. cayetanensis are in an unsporulated (immature) stage when passed in feces and so you won't see sporozoites within them like you sometimes can with Cryptosporidium spp. oocysts. Instead you may just see globular material like in the figure A (wet prep; arrows) from this case:

The immature nature of freshly-shed C. cayetanensis oocysts has an important impact on this parasite's epidemiology. Because the oocysts are shed in an unsporulated state, they must undergo further development in the environment before becoming infective. Once mature, soil or water containing the oocysts must then be allowed to contaminate food (e.g. fruits and vegetables) or drinking water, which is then consumed by humans. Humans are the only known host of C. cayetanensis and thus there are no animal reservoirs contributing to the environmental contamination.

The bottom line is that for human infection to occur, human feces must first contaminate the environment and subsequently get into food or water. Other humans must then eat this contaminated food or water. This explains why cyclosporiasis is seen primarily in settings with inadequate sanitation facilities. In resource-rich settings, most cases are seen in travelers, or are linked to consumption of imported fruits or vegetables from endemic countries. You can read about the current cyclosporiasis outbreaks in the United StatesCanada, the United Kingdom, and Europe. As I mentioned in the case introduction - this is a very timely discussion!

Of note, the life cycle is a bit different for Cryptosporidium spp. Understanding the differences allows us to understand why Cryptosporidium is endemic in resource rich countries while C. cayetanensis is not. One of the most important differences is that the oocysts of Cryptosporidium spp. ARE infective when passed in stool. They do not need to enter the environment to mature. Instead, they can be passed directly from person to person on contaminated hands or fomites. An infected person can also contaminate water sources (e.g. swimming pools) by shedding even a small (~100) number of microscopic oocysts. Since the oocysts are immediately infective, other individuals can become infected if they accidentally swallow some of the contaminated water. The second important difference between life cycles is that there are animal reservoirs for some of the Cryptosporidium species that are infective to humans. Therefore, prevention is not as simple as controlling for human fecal material. These are important facts that I try - hopefully successfully - to impart to all of my medical students, pathology residents, and fellows when I teach them about human parasites.

Thursday, August 17, 2017

Case of the Week 456

This week's case was generously donated by Idzi Potters from the Institute of Tropical Medicine in Antwerp. The following were seen in a liquid culture of a skin biopsy using Tobie Sang Lapin (TSL) medium (Phase contrast, x1000 magnification). The specimen was first ground in a dounce tissue grinder. Diagnosis?

What are these structures?

Check out their classic motility here:

Wednesday, August 16, 2017

Answer to Case 456

Answer: Leishmania sp. promastigotes.

The promastigote form is found in the Phlebotomine sandfly host as well as in Leishmania culture, which is in contrast to human infections where the non-motile amastigote form is seen . Of note, I have also occasionally seen rare promastigotes in superficial biopsies of skin ulcers.

Note that the end with the flagellum is ANTERIOR (which is counter to what you would generally expect). You can especially appreciate this while watching the movie of the promastigotes moving (go back and take a look if you missed it).

Thanks again to Idzi Potters for donating this fun case!