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. 


Sunday, October 25, 2020

Answer to Case 612

 Answer to Parasite Case of the Week 612: fly larva (maggot), Lucilia species. By using a pictorial key from the CDC website, I would say that this is most likely Lucilia (Phaenicia) sericata, the common green bottle flyThe presence of three spiracular slits indicates that this is a third instar larva (second instar larvae each have 2 slits). 

Congratulations to the many viewers who wrote in with the correct answer! As nicely explained by Idzi, Jeff, Florida Fan and Kosta, the appearance of the spiracular plate (straight slits, complete peritreme), and lack of an accessory oral sclerite points to this being Lucilia rather than Calliphora sp. 

This fly is found in most regions of the world, and feeds on dead, decaying tissue. There are several interesting features of L. sericata that are worth mentioning:

1. It is a cause of facultative myiasis in humans and animals.

2. It feeds on carrion, and is commonly used in forensic entomology to estimate the time of death.

3. It is used for maggot therapy in humans, as the larvae will effectively feed on necrotic tissue and thus aid in wound debridement. Maggots are specially raised for this purpose and disinfected prior to use. You can see some 2nd instar Medical Maggots (TM) that were sold for human maggot therapy HERE.

Florida Fan commented on how challenging it can be to get a picture perfect image of the spiracular plates. Emily and I learned at the London School of Hygiene and Tropical Medicine how to carefully prepare fly larvae for mounting to create truly beautiful preparations. However, for routine clinical use, we also like to play around with foam and applicator sticks to position the larva just right under the camera. 

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!