Sunday, June 30, 2019

Answer to Case 550

Answer to Parasite Case of the Week 550: Ascaris lumbricoides eggs, decorticated

Kudos to everyone who took the time to write in with their answer. All responses were correct! And I really enjoyed hearing about the different layers of of nematode eggs from Old One and Blaine. Here is some of the information they shared in their comments, along with some definitions:

Decorticated - To remove the bark, rind, or husk from; i.e., to remove the outer mammillated layer
Mammillated - Having relatively small protrusions from the exterior, most commonly the surface

This case happened to have both mammillated and decorticated eggs, with a large number of the latter:
When only decorticated eggs are seen, they can be confused for other helminth eggs such as hookworm and Schistosoma japonicum. Fortunately the size and thick shell can be used to reliably differentiate them.

So what are the layers of a nematode egg?  There are several (from outer to inner), as described by Old One and Blaine, with a few comments from my own research:

  1. Mucopolysaccharide/protein coat - not present in all nematode eggs; this is an exogenous product of the nematode uterus and what is referred to as the 'mammillated' albuminous layer. It is unique to each species and often stained by the bile salts of its host (yellow, orange, to brown). It is often uniquely textured during its creation. This layer may be friable, hence the decortication seen in this week's specimen. 
  2. Vitelline layer - derived from the vitelline membrane of the fertilized oocyte. It envelops the entire egg (including the bipolar plugs of Trichuris eggs). Of note, it can be selectively removed with chemical treatment, with the eggshell remaining intact (and contents remaining viable)
  3. Chitinous layer - this is the rigid layer that gives the eggs its shape. 
  4. Chondroitin proteoglycan layer - originally thought to be a lipid-rich layer
Layers 2, 3 and 4 are now commonly referred to as the trilaminar outer eggshell that we are well familiar with. Additional inner layers have since been identified, including a lipid-rich layer which serves as a permeability barrier for the developing embryo, and an innermost peri-embryonic layer. 

I had a lot of fun digging through the old and new literature to find all of this information, so thank you Old One and Blaine for the impetus to do so! NIH investigators have published a nice chapter of the structure of the C. elegans shell that is freely available HERE.

Monday, June 17, 2019

Case of the Week 549

This week's rather creepy and very cool case was donated by Dr. Matt Bolek and Christina Anaya. While the host shown here is not a human, this parasite emerging from the cricket is occasionally submitted to human clinical parasitology laboratories. What is its significance for human health?

Sunday, June 16, 2019

Answer to Case 549

Answer to Parasite Case of the Week 549: "Gordian" or "horsehair" worms, belonging to the group Nematomorpha. I had asked what its significance is for human health; this was a trick question, since gordian worms have no direct clinical significance, other than scaring people when they are found in toilet water! When submitted to the clinical parasitology laboratory, they can easily be differentiated from other large worms such as Ascaris lumbricoides by their long slender bodies:
I have to admit that I was amazed by how many worms emerged from the poor cricket in this fascinating video donated by Matt and Christina. The good news is that the cricket survived the ordeal and went on to chirp another day!

There is an excellent description of this group of worms on the University of Kentucky entomology website.

Monday, June 10, 2019

Case of the Week 548

This week's case was generously donated by Dr. Tara Ness, with filming credit to the Lab Hlathi Team in eSwatini. The following arthropod was found in the urine specimen of a man with HIV and a history of dysuria. Identification?

Sunday, June 9, 2019

Answer to Case 548

Answer: Mite, most likely Dermatophagoides species (dust mite).

As mentioned by several readers, we are lacking sufficient details to make a definitive identification. However, we can conclude that this is a contaminant in this specimen and not a cause of the patient's symptoms. As Blaine mentioned, this is a "Conta-mite-nt"!

Some readers mentioned that Sarcoptes scabei should be considered. While this is also a mite, its distinctive features, including its short legs and overall body shape, allow for differentiation from Dermatophagoides:

Thanks again to Dr. Ness and her lab for donating this case.

Monday, June 3, 2019

Case of the Week 547

Here is our monthly case by Idzi Potters and the Institute of Tropical Medicine, Antwerp.

The following 1-cm long structure was extracted from a Belgian patient returning from Ghana. Identification?

Sunday, June 2, 2019

Answer to Case 547

Answer to Parasite Case of the Week 547: Cordylobia rodhaini, also known as Lund's fly.

As noted by Bernardino, this is a 3rd instar larva, with a characteristic shape, size, irregularly-placed, weakly-pigmented cuticular spines and spiracles for this species. The more sinuous spiracles allows us to differentiate this from Cordylobia anthropophaga, the "tumbu fly" which is more commonly seen on humans. Both are found in the African subtropics.

From Old One:
Hooray for Bernardino a wiz at diagnostics
Lund’s fly no match for his skillful forensics
The folks on the blog all think he is swell
Never missing his mark, the new William Tell

You can read all about this fascinating parasite in Idzi's latest publication which is freely available HERE. An important point to note is that the adult flies of C. rodhaini and C. anthropophaga deposit their eggs on soil or clothing. Contact with the warm-blooded host then causes the larvae to hatch and penetrate the skin. This is why it is common practice in endemic areas to iron your clothes - including undergarments - after taking them off the line! This important point can be remembered from Blaine's fun poem:

In Africa, if you allow your laundry to air dry
Make sure you iron it! Wanna know why?
'cuz this diabolical dipteran lays its eggs on fomites
especially on clothes and sheets dried by sunlight
and that's how you get exposed to the tumbu fly!

Thanks again to Idzi for sharing this case with us!