Monday, October 26, 2020

Parasite Case of the Week 612

This week's case comes from my own lab - images by my awesome technical specialist, Emily Fernholz. The following object was submitted for identification. No clinical history was available. 


Monday, October 19, 2020

Case of the Week 611

 This week's lovely case is from Dr. Phillip Heaton. The following was submitted to his laboratory for identification. What is shown here? And what does the red arrow in the first image point to?

Sunday, October 18, 2020

Answer to Case 611

 Answer to Parasite Case of the Week 611: Female crab louse, Pthirus pubis, with an egg. She's a mom to be!

Florida Fan pointed out that we would be able to tell that this was a female louse, even if she wasn't gravid, due to the somewhat flattened, indented posterior (vs. the rounded posterior of the male).

Dr. Heaton was also kind enough to provide a beautiful egg (nit) from this case. It shows the classic features of a P. pubis nit, with a raised operculum:

This is in comparison to the flattened operculum of Pediculus humanus eggs:
Be sure to read the comments for some fun and helpful information, including an explanation from Kosta in why this louse's genus name is spelled Pthirus instead of Phthirus

Tuesday, October 13, 2020

Case of the Week 610

I have a fun case for you this week from Dr. Richard Bradbury! The following structures were seen in a stool sample from 2-year old child from a rural southern Australia with mucoid diarrhea, abdominal pain and poor weight gain. Both an unstained web prep and iodine-stained prep are shown. The size of these objects ranges from 26–32 μm long by 16–17.5 μm wide. Identification?

Monday, October 12, 2020

Answer to Case 610

 Answer to Parasite Case of the Week 610: Brachylaima cribbi, a parasitic trematode found only in Australia to date. B. cribbi infects land snails and slugs as first/second intermediate hosts, and employs a wide range of mammals, reptiles, birds and amphibians as definitive hosts. The first human infections were published in 1996 by Dr. Andrew Butcher, who also wrote an excellent review on this parasite. Dr. Butcher recently passed away, and so I am dedicating this post to him and his important work. Humans become infected after ingesting undercooked snails. The main symptoms that have been reported with infection are watery, mucoid diarrhea, abdominal pain, anorexia, and weight loss. 

The eggs of this parasite are quite interesting in that they are small (only ~30 μm long), have an inconspicuous operculum, and are flattened on one side. They also have an abopercular knob or thickening. The eggs are usually fertile when seen in stool, with a well-developed miracidium. However, infertile eggs have also been seen in chronic infections; they are smaller and lack an internal miracidium. We can see both fertile and infertile eggs in this case:

You can really appreciate the infertile nature of an egg in this image:

Some readers suggested that this parasite might be Clonorchis sinensis or Opisthorchis sp., given the small size and presence of an operculum. However, we can exclude these parasites based on the lack of travel and the asymmetric flattening of one side. The flattened side of the eggs likely led some to suggest that this is Enterobius vermicularis; however, this parasite be excluded by the small size and presence of an operculum. The operculum also allows us to exclude artifacts and parasite mimics such as pollen and mushroom spores. 

So in many ways, a fascinating case! Thanks again to Dr. Bradbury for donating this case.

Monday, October 5, 2020

Case of the Week 609

 This week's case features our monthly case from Idzi Potters and the Institute of Tropical Medicine, Antwerp. The following structure was seen in a urine sediment. No further history is available. Identification?

Sunday, October 4, 2020

Answer to Case 609

 Answer to Parasite Case of the Week 609: Not a parasite egg.

Idzi and I debated over what this is exactly but couldn't come up with a good answer. I like Old One's, Florida Fan's, and Sir Galahad's suggestion that it could be a mushroom spore. Regardless, it is too small and irregular to be a Schistosoma haematobium egg, and it lacks the features for other parasite eggs - all good news for the patient. Sam queried if this could be a uric acid crystal, which is a good thought. However, uric acids have a slightly different appearance in my experience (see previous posts HERE).

As Sheldon, Marc and Nandhu point out, we can exclude S. haematobium based on the following features: 

  • There is no miracidium inside of the egg
  • The eggs is only ~75 micrometers long (expected size for S. haematobium is 110 - 170 micrometers)
Thanks to everyone who wrote in on this case!

Wednesday, September 30, 2020

Case of the Week 608

 This week's case is from Dr. Peter Gilligan. It's a histopathology image - which I know isn't always popular with the classical parasitologists! But I think you might be able to take a stab at the diagnosis regardless. The following eggs were seen in an ulcerated area of an intestinal biopsy. They measure approximately 30 micrometers in diameter. Identification?

Tuesday, September 29, 2020

Answer to Case 608

 Answer to the Parasite Case of the Week 608: Taenia sp. egg. The eggs are those of T. solium, T. saginata, or T. asiatica, but it is not possible to tell the species from the egg alone. You can find more informations about these interesting cestodes on the CDC's DPDx website.

Note the classic small size (30-35 micrometers in diameter) of the eggs. Each have a thick radially-striated outer wall and internal 6-hooked oncosphere. 

The hooks aren't easily visible with H&E, but they are refractile when viewed with a narrowed condenser. It is likely that the eggs were released from a mature gravid proglottid in the large intestine and made their way into an ulcerated region of the mucosa where they were an incidental finding on biopsy. Taenia solium and T. saginata do not invade the mucosa (other than at the point where the hooklets anchor the adult worm's scolex to the small intestine), so there must have been some other condition present that caused the intestinal disruption in this patient.

Some readers commented that this could also be Echinococcus sp. if this was a canid rather than a human host. Echinococcus spp. adults are found within the canid definitive host and the eggs are shed into the environment where they are ingested by herbivore intermediate hosts. Humans are accidental intermediate hosts. After ingesting the eggs from the environment, the eggs hatch in the small intestine to release the oncosphere. Thus we wouldn't expect to see intact Echinococcus sp. eggs in humans. The oncospheres penetrate the wall of the human host and enter the circulatory system to travel to the organs (usually the liver) and form the cystic form of the parasite.

Thanks again to Dr. Gilligan for donating this fascinating case!

Monday, September 21, 2020

Case of the Week 607

 This week's case was donated by my colleague, Dr. Tom Grys. Tom and I did our Clinical Microbiology fellowship together and had a lot of fun! 

The following specimen was brought in by a patient after finding it near his eye upon wakening. He is concerned that it might be an ectoparasite or vector of human pathogens, and is hoping that the laboratory can provide this information. What is your identification, and how would you counsel the patient or patient's clinician?