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?

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:

Identification?

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!

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?

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.

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?

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.

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.

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.

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?