Case of the Week 788

Happy Autumn, everyone! It's the first Monday of the month and time for our monthly case from Idzi Potters and the Institute of Tropical Medicine, Antwerp. The following were seen in a direct wet mount specimen of stool from a patient with chronic constipation. What is your identification?

Case of the Week 787

 This week's case is from Dr. Beth Adams who encountered a patient in the Moskitia region of Honduras who had coughed up the following object. What is your presumptive identification?

Answer to Case 787

 Answer to the Parasite Case of the Week 787: Adult Ascaris sp.

As Florida Fan and Idzi noted, the curved posterior end suggests that this is a male adult. 

Ascaris is the largest nematode to reside in the human intestinal tract. Adults live in the small bowel and must move against peristalsis to avoid being expelled in the stool. The fact that they are freely moving and not attached to the intestinal wall means that they can occasionally end up in ectopic locations such as the biliary tree or appendix. In this case, the worm migrated up the intestine, stomach, and esophagus, and was expelled through the mouth (!) Given its large size, heavy infections can lead to the potential deadly complication of small bowel obstruction.  

Some readers made the interesting point that this could be either Ascaris lumbricoides or the zoonotic Ascaris suum, which raises the controversial topic of Ascaris taxonomy!.Although they were long thought to be separate species, Ascaris suum was found to be genetically similar to the human species A. lumbricoides in a 2014 comparative analysis of microRNA profiles, arguing against separation into Ascaris two species. However, a 2020 analysis using whole genome sequencing found significant genetic differentiation between A. lumbricoides and A. suum populations. Therefore, it looks like the two populations are genetically distinct and likely deserve separate classifications. We can hopefully look to future analyses to more fully understand their taxonomic status.

Thanks again to Dr. Beth Adams who donated this case, and to Drs. Mike Adams and Bill Stauffer who shared the image and video with me initially.

Case of the Week 786

 This week's case was generously donated by Dr. Richard Bradbury from James Cook University in Australia. The following object was seen in the stool from a patient with advanced HIV infection living in Tanzania. Shown are preparations using differential interference contrast (DIC), darkfield, and fluorescent microscopy (wavelengths unknown). The objects measure approximately 25-30 micrometers in length. What is your identification?

Answer to Case 786

 Answer to the Parasite Case of the Week 786: Cystoisospora belli

Idzi nicely described this finding as an "Immature oocyst of Cystoisospora belli (formerly known as Isospora belli) containing only one sporoblast, which will evolve to two sporoblasts and later on will sporulate to become infective." 

While we don't know the definitive details of the images that Dr. Bradbury provided, Idzi suggested that "the last one could be autofluorescence at 450-490 nm." and noted that "All coccidia (including Cystoisospora belli) will demonstrate fluorescence (without prior staining) when placed under UV-light. They will show up as bright blue structures when using an excitation filter of 330-365 nm, or green at 450-490 nm. Of note: Cryptosporidium is not placed among the coccidians anymore (moved to the Gregarines), and does not demonstrate autofluorescence either!"

If you are interested about how autofluorescence can be used for diagnosis, you should check out Blaine's and Dr. Marc Couturier's recent paper "Shedding new light on Cyclospora: how the use of ultraviolet fluorescence microscopy can improve diagnosis of cyclosporiasis".

Case of the Week 785

It's the first of the month and time for a case from Idzi Potters and the Institute of Tropical Medicine, Antwerp! 

The following images show an object that dropped out of a patient's nose 😮. What is your identification?

Wishing all of my American readers a very happy and restful Labor Day.

Answer to Case 785

Answer to the Parasite Case of the Week 785: Oestrus ovis larva.

This is a fascinating case of a probable 2nd instar stage of Oestrus ovis, commonly known as the sheep nasal botfly. O. ovis, can occasionally cause infection of the eye (ophthalmomyiasis) or, less commonly, the nose and sinuses (rhinomyiasis) in humans. Human infection is an accidental zoonosis and results from deposition of first-instar larvae by adult flies, typically in the ocular or nasal mucosa. Human cases are most prevalent in Mediterranean and other subtropical regions, with seasonal peaks in summer and spring. 

Most infestations are self-limited as larvae rarely progress beyond the first instar in humans. Therefore, this is a very interesting presentation of what appears to be a 2nd instar larva involving the nose and/or sinuses. 

Diagnosis is based on clinical suspicion and examination of the larvae. First-stage larvae are small (approximately 1–2 mm) and mostly translucent As noted above, this is the most common form seen in humans. 

Second-stage larvae are larger (up to 7 mm), more robust, and display increased segmentation, with the body becoming more opaque and the cuticle developing small spines. The oral hooks are more prominent, and the posterior spiracles begin to show more complex structure. This is what I believe this specimen to be.

Third-stage larvae are the largest (up to 21 mm), cylindrical, and have a thick, heavily pigmented cuticle with pronounced transverse bands of spines and well-developed oral hooks in their mature form; the posterior spiracles are fully formed and more sunken into the body. Also, the body is distinctly segmented, and takes on a brown color in the mature form.

Check out these two publications for some great photos of the different stages:

b105_pp382-387.pdf

Prevalence Rate and Molecular Characteristics of Oestrus ovis L. (Diptera, Oestridae) in Sheep and Goats from Riyadh, Saudi Arabia

Thanks to all who wrote in on this interesting case, and to Idzi for donating it! Special thanks to Blaine Mathison for his input on larval stage.

Case of the Week 784

This week's case was generously donated by Rebecca Black, a Veterinary Medicine student training in Minnesota, USA. She was able to help this poor little kitty get the care it needed. What is your diagnosis? Does this organism pose a risk to humans?

Answer to Case of the Week 784

Answer to the Parasite Case of the Week 784: Myiasis causing fly larva, most likely Cuterebra species. 

Thankfully, Rebecca Black and her colleagues were able to remove the larva from this poor kitty! 

As noted by Florida Fan and others, we don't have the posterior spiracles to make a definitive identification. However, based on the presentation, geographic location, dark color, and overall appearance, we can still make an identification of Cuterebra sp. third instar stage larva.

Note the dark color and small spines covering most of the body. 

If you are interested, you can read more about this infection in animals at the following excellent sites:

Cuterebra Infestation in Small Animals - Integumentary System - Merck Veterinary Manual

Companion Animal Parasite Council | Cuterebriasis

Genus Cuterebra - Rodent and Lagomorph Bot Flies - BugGuide.Net

The usual hosts of Cuterebra are rodents and lagamorphs. Flies lay eggs on vegetation or woody ground debris, often near the opening of rodent burrows. The eggs hatch to release a first instar stage larva when there is exposure to increased temperature, indicating the presence of a nearby host. The larva then enters host through any natural body opening such as the mouth or existing wounds. It will then migrate to the subcutaneous tissues and enlarges rapidly. It creates a pore from which it can breathe and eventually exit the host, usually in 3-6 weeks. 

As you all know, my interest is in human infections, and therefore I posted this case as both a pet lover and a human medical parasitologist. Cuterebra infections (cuterebriasis) can rarely occur in humans, and as with other forms of myiasis, removal of the larva is curative.

Thanks again to student veterinarian, Rebecca Black, for donating this case! 

Case of the Week 783

This week's case was generously donated by Dr. Richard Bradbury. The following were seen in a stool specimen from a middle-aged man with diarrhea. Preparations are a concentrated wet prep and trichrome stained permanent mount. Object measure 10-15 micrometers long. What is your identification?