Sunday, March 30, 2008

Case of the Week 15

Welcome to the Parasite Case of the Week. Every Monday there will be a new case, as well as the answer to the previous case (you will find it below the corresponding case). Please feel free to leave a comment or your thoughts regarding the diagnosis. Enjoy!

The following images were taken from a heart at autopsy and stained with hematoxylin and eosin (Top to bottom magnification: 200x, 400x, 400x). CLICK ON THE IMAGES TO ENLARGE


















Diagnosis?
Based on the morphology, what is your differential diagnosis?

Answer to Case 15

Answer: Typanosoma cruzi amastigotes. This intracellular collection of T. cruzi amastigotes is referred to as a 'pseudocyst' since there is no true cyst wall.

The location (heart muscle) is useful in making the diagnosis since this is a classic site for T. cruzi in humans, but it's important to keep in mind that pseudocysts can form in other organs and in skeletal muscle.

The principal differential diagnosis based on this morphologic appearance includes Histoplasma capsulatum yeasts and Leishmania amastigotes. Instead of forming a pseudocyst, however, they both reside within macrophages and the collection of organisms will be much smaller.

Congratulations to Tom and Dr. R for getting the correct answer for this case. Tom also added the following for those of you who enjoy learning aids (myself included):

"T cruzi is known for lots of C's.

Cruzi
Chagas disease
C-shaped (referring to the tryptomastigote blood stage)

If you want to get a little more Crazy, here are some more:
Cardiac tissue
Central & South America
Cheek swelling near eye (Romana's sign)
Chronic infections are common
Colonic infection (megacolon)
Crap from Reduviid bugs, which contain the trypanosomes, and gets inoculated into the bite wound by scratching."

I would also add in Cysts (pseudocysts), as shown in this case.

Sunday, March 23, 2008

Case of the Week 14

Welcome to the Parasite Case of the Week.
Every Monday there will be a new case, as well as the answer to the previous case (you will find it below the corresponding case). Please feel free to leave a comment or your thoughts regarding the diagnosis. Enjoy!

The following can be found in your backyard - in a flowerpot filled with water or an ornamental pond. They are one stage in the life cycle for which organism? Click on image to enlarge.









Watch 'em wriggle:
video

Bonus for entomology students: What subfamily is represented here?

Answer to Case 14

Question: They are one stage in the life cycle for which organism?
Answer: mosquito

I've heard from several of you (on-line and off) that you've hosted little families of these yourselves! It's an easy thing to do.

Congratulations to Heather for getting the correct subfamily Bonus Question. These are of the Culicine subfamily, which includes Culex, Aedes, and Mansonia mosquitoes. What they all have in common is the presence of a little siphon that allows them to breathe while hanging upside down from the surface of the water. That's how you can distinguish these from Anophiline mosquitoes which lack a breathing siphon and lay parallel to the surface of the water. Here's more detail on the siphon:

Image 1 - Culex larvae in a small container of water. (Click on image to enlarge)











Image 2 - microscopic detail of the siphon. Note that the siphon connects with breathing tubes that go into the body of the larva.










Here's a link to a great illustration which demonstrates the difference in breathing mechanisms between Anophelines and Culicines (Culicine mechanism - left, Anopheline mechanism - right)

http://www.utep.edu/LEB/mosquito/larvslide3.htm

Finally, by request, I've expanded the answer from my last case to further describe
Entamoeba moshkovskii. If you're interested, please take a look below.


Images were taken at the London School of Hygiene and Tropical Medicine and shown with Permission.

Sunday, March 16, 2008

Case of the Week 13

Welcome to the Parasite Case of the Week.
Every Monday there will be a new case, as well as the answer to the previous case (you will find it below the corresponding case). Please feel free to leave a comment or your thoughts regarding the diagnosis. Enjoy!

The following was seen in an formalin-fixed iodine-stained wet mount fecal preparation. It is approximately 15um in diameter. Other examples of the organism in this sample all measure 12-15 um and have 4 nuclei or less. Click on the image to enlarge.

Name 3 possible diagnoses.











Image was taken at the London School of Hygiene and Tropical Medicine. Used with Permission.

Answer to Case 13

3 Possible diagnoses for the above cyst:
Entamoeba histolytica
Entamoeba dispar
Entamoeba moshkovskii

These 3 organisms are morphologically identical, yet genetically distinct, and only E. histolytica has definitely been shown to cause human disease. I also would have accepted immature E. coli. E. hartmanni would not be included in the differential given the size of these organisms (15um).

I'll say a few words on E. moshkovskii since most of you probably haven't heard of it before. Even though it was first described 1941, it was thought at that time to be only an environmental organism. However, it has now been identified in human fecal samples worldwide. The true prevalence is not well understood, and this is partially because it cannot be distinguished from E. histolytica and E. dispar by light microscopy. There is some evidence emerging that it may be associated with human disease, so I'm sure we will continue to hear more about it in the future.

Sunday, March 9, 2008

Parasite Case of the Week 12

Welcome to the Parasite Case of the Week.
Every Monday there will be a new case, as well as the answer to the previous case (you will find it below the corresponding case). Please feel free to leave a comment or your thoughts regarding the diagnosis. Enjoy!

This egg measures 55 um in length. Focusing up and down highlights important structural features. Click on images to enlarge.

Identification?
What other parasite egg has a similar appearance and how can you differentiate it?








Images taken at the London School of Hygiene and Tropical Medicine. Shown with permission.

Answer to Case 12

Everyone who wrote in got this one correct (I guess I made it too easy!)

Identification: This is a Capillaria egg.

What other parasite egg has a similar appearance and how can you differentiate it? Trichuris trichuria or whipworm eggs have a superficial appearance to Capillaria eggs, but do not have a striated shell and have much more prominent polar plugs.
Here are two the next to each other for comparison. I find the striated wall to be the most useful feature for identifying Capillaria eggs.






















For those of you who are a little more advanced, you may be interested in the answer to Heather's question:

She asked whether it is possible to differentiate the eggs of Capillaria spp. The answer is YES: there are some subtle differences between the eggs of C. hepatica (such as the one shown) and those of C. philippinensis. Both can be found in the stool and have a striated cell wall, but C. philippinensis eggs are described as more "peanut" or "barrel" shaped with inconspicuous polar plugs, while C. hepatica eggs are more rounded and have more prominent polar plugs. C. hepatica eggs are also slightly larger (50-60 um) than C. philippinensis eggs(35-45 um). For comparison, T. trichuris eggs are 50-55um.

Sunday, March 2, 2008

Parasite Case of the Week 11

Welcome to the Parasite C.O.W.
Every Monday I will post a new case, as well as the answer to the previous case (you will find it below the corresponding case). Please feel free to leave a comment or your thoughts regarding the diagnosis. Enjoy!

These 1 to 1 and 1/2 inch worms take up residence in human mesenteric veins.

Questions:
Identification?
How many worms are present in this video?

video
Video taken at the London School of Hygiene and Tropical Medicine. Shown with permission.

Answer to Case 11

A lot of people seemed to like this case, although I was accused of being 'naughty' for displaying Schistosome worms in copulo. There are at least 3 worms present - 1 married couple and a bachelor (as per Anonymous), although I would give credit to those who said 4 since you couldn't see all of the worm on the left.

To answer Heather's question, these are S. mansoni adults, although the features to distinguish them from other species (cuticle and internal structures) are not obvious here.

In case some of you could not tell the male and females apart, here is a diagram (click image to enlarge):