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



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!

Monday, August 7, 2017

Case of the Week 455

This week's impressive case was donated by Dr. Peter Gilligan and Dr. John Hunt. The patient is a middle-aged man from Nigeria who presented with signs of increased intracranial pressure including nausea and vomiting. An MRI showed dilated ventricles and irregular lesions in the cerebellum. Below is the material that was resected:

The following are H&E-stained images of this material. Identification?

Sunday, August 6, 2017

Answer to Case 455

Answer: Coenurosis, an infection with the larval form of either Taenia serialis or T. multiceps. While the the former has a predilection for soft tissue, the latter commonly involved the eye and central nervous system and is the likely 'culprit' in this case. The multicystic nature and presence of multiple protoscoleces within a cyst is characteristic for coenurosis and allows this infection to be differentiated from cysticercosis which only has one protoscolex per cyst.
Also note that the protoscoleces are larger and more complex than those of Echinococcus species, allowing us to rule out this similar cestode infection.
The CDC DPDx group has some great information and photographs of coenurosis which you can find here:

Thank you to everyone who wrote in on this challenging case, and kudos to Blaine for getting it correct!