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:

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!

Monday, July 31, 2017

Parasite Case of the Week 454

This week's case was generously donated by Florida Fan. The patient is an otherwise well woman in her 30's who passed the following object in her stool:

The following object was also observed in her stool. It measured approximately 50 micrometers in length. Identification?

Sunday, July 30, 2017

Answer to Case 454

Answer: Tapeworm, Diphyllobothrium species

This case shows the classic morphology of an adult tapeworm, consisting of a flat ribbon-like body composed of multiple repeating units called proglottids. This particular tapeworm can be identified by the morphology of its proglottids and eggs. The proglottids are broader/wider than they are long; hence the name the "broad fish tapeworm". Within the center of each proglottid is a central uterine structure which is often visible macroscopically. In this case, it can be seen as a central 'hump' in each proglottid:
The eggs are also characteristic for this genus and allow for differentiation between Diphyllobothrium and Taenia species. Note the thin wall, oval shape, intermediate size (55-75 micrometers long) of the egg and the operculum (lid-like opening) at one end. In many cases, a knob-like structure can be seen at the other end (abopercular knob), but it is not clearly visible in this case.
The most reliable means for identifying the infecting Diphyllobothrium species is through molecular testing. While D. latum is the most common cause of human infection worldwide, other species that can infect humans include D. pacificum, D. yonagoensis, D. dendriticum, D. dalliae, D. cordatum, D. ursi, and D. lanceolatum.

Saturday, July 22, 2017

Case of the Week 453

This week's case was kindly donated by one of my former Clinical Microbiology fellows, Dr. Adam Caulfield. The specimen (shown below) was extracted from the leg of a 70 year old man who had recently returned from a trip to Costa Rica. It measures approximately 1.5 cm in length. Identification?

Friday, July 21, 2017

Answer to Case 453

Answer: Bot fly, Dermatobia hominis

As mentioned by Florida Fan, the body has spiky projections and general body habitus consistent with myiasis. Of note, the cuticular spines are lacking on the terminal 3 body segments which, along with the travel history, are consistent with Dermatobia hominis. Ideally we would also like to look at the posterior spiracles to confirm the identification, but photos weren't available from this case.

Tuesday, July 11, 2017

Case of the Week 452

This week's case was generously donated by Dr. Richard Bradbury. The following biphasic population of organisms was seen after corneal scrapings were inoculated onto a non-nutrient agar overlain with Escherichia coli and incubated for several days.

These objects measure approximately 25 micrometers in diameter.

These objects measured up to 45 micrometers in greatest dimension:


Monday, July 10, 2017

Answer to Case 452

Answer: Acanthamoeba species cysts and trophozoites. The diagnosis can be made by the characteristic morphology in conjunction with the clinical history. As mentioned by Florida Fan, the trophozoites have thorny or spiny projections called acanthopodia (from the Greek akantha meaning thorn), whereas the trophozoites of other amebae have rounded ends on their pseudopodia/projections.

The source (cornea) is also characteristic for this organism. Richard Garcia-Kennedy mentioned that not changing the contact lens case regularly is a common risk factor. Other important risk factors are cleaning contact lenses (or the case) with tap water and swimming while wearing lenses. I think I've scared all of my residents and Clinical Microbiology fellows out of these bad habits!

Like Rune, we have switched over to PCR for detection of all free-living amebae from clinical specimens. However, we used to use tap water agar (overlain with a bacterium like E. coli as a food source), and we would also occasionally supply our "cornealogists" with culture plates that they could directly inoculate. However we mostly had our clinicians send us specimens in MEM (minimum essential medium) which also worked quite well in supporting growth and viability until we could inoculate the specimen onto culture. When positive, corneal specimens and contact lenses usually grew Acanthamoeba within 24 hours (and in one memorable case, within 8 hours), but the PCR provides an even faster result and has proven to be just as sensitive as culture. It also allows us to detect Balamuthia mandrillaris (which won't grow on non-nutrient agar) and Naegleria fowleri (where time is of the essence for detection).

Thank you all for the comments on this case, and thanks again to Richard for donating it!

Monday, July 3, 2017

Case of the week 451

Happy July 4th to my American readers! Here is a nice red, white and blue case for you. The following objects were seen in a stool specimen stained with a modified acid fast stain. They measure approximately 35 micrometers in greatest dimension. Identification?

Sunday, July 2, 2017

Answer to Case 451

Answer: Cystoisospora belli (formerly Isospora belli) oocysts

As with Cyclospora cayetanensis and Cryptosporidium oocysts, the oocysts of C. belli stain red/pink using modified acid fast and modified safranin stains (below, right), with unstained "ghost" cells (below, left) also commonly seen. The oocysts are immature when shed in stool and contain only a single sporoblast. Oocysts will then mature in the soil, during which time the sporoblast divides into 2 sporoblasts  and develop cyst walls, becoming sporocysts. Each sporocyst will contain 4 sporozoites - the form that invades the intestinal epithelial cells.

Monday, June 26, 2017

Case of the Week 450

This week's case is generously donated by Dr. Kamran Kadkhoda. This little arthropod was discovered in Manitoba, Canada. Identification?

Sunday, June 25, 2017

Answer to Case 450

Answer: Dermacentor variabilis

The CDC has a nice basic pictorial identification key that you can access HERE. This key will walk you through the identifying features of hard ticks, and Dermacentor species specifically. Differentiating D. variabilis from D. andersoni (and other Dermacentor spp.) is a bit trickier and is based on the size and number of goblets on the spiracular plates; while Dermacentor variabilis has more than 300 small goblets, D. andersoni has 100-200 moderately sized goblets.

I particularly like Ellen's analogy, in which she described the goblets of D. variabilis as 'grainy' while those of D. andersoni resemble Cheerios.

The location where this tick was found (Manitoba, Canada) also helps differentiate the two. Dermacentor variabilis has undergone a range expansion in the Canadian Prairies since the 1960s (see Dergousoff et al. J Med Entomol 2013) so that D. variabilis is the species we would expect to see in Manitoba.

Monday, June 19, 2017

Case of the Week 449

The following object was found in a toilet and submitted to the parasitology lab. Identification? What is the significance of this finding? Images taken by my fabulous education specialist, Emily Fernholz.

Sunday, June 18, 2017

Answer to Case 449

Answer: rat-tailed maggot, family Syrphidae

As nicely described by one of my readers, David Bruce Conn, "This is a rat-tailed maggot, larva of a hover fly belonging to the family Syrphidae. This one may be of the common genus Eristalis. They are not parasitic, but typically live in stagnant water and feed on organic material before pupating. They may incidentally live in toilets and latrines."

The larvae are very recognizable, a long "tail" that contains a breathing tube (respiratory siphon) that connects to the tracheal system and allows the larva to breath oxygen from the water surface. You can also make out antennae and prolegs.

I should note that there have been a few reports of facultative myiasis by this group, but in further investigating these references, I couldn't find any definitive evidence that this occurs (the specimens were all brought in by the patient after being found in the toilet.) Therefore, I think that unless definitely proven, all cases of rat-tailed maggots should be considered incidental findings due to environmental contamination.

Wednesday, June 7, 2017

Case of the Week 448

This week's beautiful case was donated by Florida Fan. These objects were identified during colonoscopy from a middle-aged man. No further history is available. Identification?

Tuesday, June 6, 2017

Answer to Case of the Week 448

Answer: Trichuris trichiura adults

The photos in this case show most of the characteristic identifying features of adult T. trichiura (a.k.a. whipworms) including the classic "whip" shape and eggs with bipolar plugs. The full adult shown is a male as evidenced by his reproductive structures and curled tail. Note that the skinny end is the anterior aspect and not the tail like many students of parasitology would initially assume. The full body of the female is not shown, but you can see characteristic eggs coming out of the uterus.

The stichosome is clearly visible in some of the photos; this prominent glandular organ is seen in trichurids such as Trichuria and Trichinella (as well as some other nematodes) and consists of a row of multiple unicellular cells called stichocytes. The stichosomeruns along the posterior aspect of the esophagus and is a key identifying feature in both intact and sectioned worms. The stichosome opens into the esophageal lumen and has both secretory and absorptive functions.

Monday, May 29, 2017

Case of the Week 447

This week's case is in honor of Memorial Day and was generously donated by Florida Fan. I've actually revived this from a previous case, since the colors (red, white and blue) are so beautiful with Florida Fan's rendition of the modified safranin stain. The red objects seen below were found in stool and measure approximately 10 micrometers in diameter.


Sunday, May 28, 2017

Answer to Case 447

Answer: Cyclospora cayetanensis oocysts

The beautiful red staining of these round oocysts is characteristic, whether using the standard modified acid fast stain or the modified safranin stain.

Monday, May 15, 2017

Case of the Week 446

This week's very timely case was donated by George at Memorial Sloan Kettering Cancer Center. The following objects were seen in a wet mount of a concentrated stool specimen. They measure less than 20 micrometers in dimension and do not have an apparent operculum.

Here is their appearance using iodine: