Case of the Week 137

This following amazing case was generously donated by Dr. Donald Jungkind at Thomas Jefferson University Hospital, Philadelphia, PA

The following objects were seen in a CMV shell vial viral culture from a bronchial aspiration.



(CLICK ON IMAGES TO ENLARGE)

Shell vial


Iodine-stained preparation:


Evidence of this parasite was also seen on the blood agar plate for bacterial culture.


Identification?

Answer to Case 137

Answer: Strongyloides larvae identified in a respiratory specimen.

Although larvae in a respiratory specimen could be due to a number of different organisms, including hookworm, Ascaris, and Strongyloides, the overall length of the worm and clinical history were most consistent with Strongyloides.

The larvae may be identified by morphologic exam on stool or sputum, as well as by stool culture and concentration methods. Culture has been shown to be the most sensitive, and should be considered when there is a suspicion of strongyloidiasis. For culture, a stool or respiratory specimen containing bacteria is placed on an agar plate and incubated. A clear or blood agar can be used. The larvae will move through the agar, dragging the bacteria along with them, creating the macroscopic tracks that are visible in this case (below). Note that other worms, including hookworm, will also cause this phenomenon.



This amazing case further emphasizes the potential infectious nature of all human specimens that are submitted to the laboratory. Both the shell vial and the bacterial agar plate shown here contain infectious larvae that could penetrate intact skin and cause human infection. For this reason, it is important for all microbiologists to be familiar with the appearance of Strongyloides tracks and larvae and use appropriate infection control measures. Thanks again to Dr. Donald Jungkind for sharing this unusual case!

Case of the Week 136

The following punch biopsy was submitted for identification of an ectoparasite.
(CLICK ON IMAGES TO ENLARGE)




Identification?
What is the preferred method for removing this ectoparasite?

Answer to case 136

Answer: Ixodes spp. tick
As FP from VT mentioned,
"This is an Ixodes hard tick. Could be scapularis, scutal plate is the right shape. Need to see the capitulum. If this tick came thru our lab, without the capitulum we would call it Ixodes sp. unable to r/o scapularis."

Of course, I. scapularis is a tick of concern, since it is the vector of anaplasmosis, Lyme disease, and babesiosis. It is also a possible vector of the Ehrlichia muris-like organism that was recently described from Minnesota and Wisconsin.

What is the preferred method for removing this ectoparasite?
As Anonymous said:
"Best way to remove it is grab the tick by the head using forceps and pulling straight out. Being careful not to break apart."

I showed this case as an example of the way NOT to remove a tick. Forceps will do an acceptable job, and there is no need to perform a punch biopsy (which I think we would all agree is overkill)!

Case of the Week 135

The following objects were seen on a stool ova and parasite examination from a patient with diarrhea and abdominal pain. They measure approximately 80 micrometers in greatest dimension. Identification? What feature makes this parasite unique?

Answer to Case 135

Answer: Balantidium coli trophozoites.

These protozoa are distinguished by their large size, cilia, and "kidney-bean" shaped nucleus.

What feature makes this parasite unique? They are the only ciliated protozoan to infect humans.

Case of the Week 134

The following were an incidental finding at autopsy. Shown are hematoxylin and eosin stained sections of human tongue. (CLICK ON IMAGES TO ENLARGE)

100x original magnification


200x original magnification


200x original magnification

Diagnosis?

What is the most common source of infection worldwide? What about in the United States?

Answer to Case 134

Answer, Part I: Trichinella spp. Although Trichinella spiralis is the most common species to infect humans in the United States, it is generally not possible to speciate based on morphologic features. The exception is Trichinella pseudospiralis whose larvae are not encapsulated compared to T. spiralis, T. nativa, T. nelsoni, T. britovi, and T. murrelli which do have encapsulated larvae. These species are the predominant to infect humans.

Answer, Part II: What is the most common source of infection worldwide? Domestic pigs. What about in the United States? Wild game

According to a publication by the Centers for Disease Control and Prevention (Roy et al."Trichinellosis Surveillance --- United States, 1997--2001." Centers for Disease Control and Prevention), trichinellosis has been steadily decreasing in the United States due to tightened regulations on pig farming and pork processing. They state:

"Although trichinellosis was associated historically with eating Trichinella-infected pork from domesticated sources, wild game meat was the most common source of infection during 1997--2001. During this 5-year period, 72 cases were reported to CDC. Of these, 31 (43%) cases were associated with eating wild game: 29 with bear meat, one with cougar meat, and one with wild boar meat. In comparison, only 12 (17%) cases were associated with eating commercial pork products, including four cases traced to a foreign source. Nine (13%) cases were associated with eating noncommercial pork from home-raised or direct-from-farm swine where U.S. commercial pork production industry standards and regulations do not apply."

The following is an excellent source of information on trichinellosis with beautiful photos: http://www.trichinella.org/index_synopsis.htm

To make the diagnosis of trichinellosis on tissue section, one needs to recognize the classic appearance of the coiled larvae within tissue (typically skeletal muscle). Here is an image from this case that nicely demonstrates the larva, nurse cell (derived by the host) and stichosome (column of large rectangular cells).
(hematoxylin and eosin stained tissue section, 200x original magnification)


Note that in this case, the larva is located in the skeletal muscle of the tongue, right below the tongue's epithelium. (CLICK ON IMAGE TO ENLARGE)
(hematoxylin and eosin stained tissue section, 100x original magnification)


It is easiest to appreciate the coiled nature of the larvae by pressing non-fixed infected muscle between 2 slides and examining the tissue under the microscope. Here is an image from a previous case of the week that demonstrates a 'squash' prep:


Finally, for those of you non-pathologists who are having a hard time envisioning how a 3-dimensional coiled worm became a series of circles and ovals in tissue section, I've created the following diagram. The top image shows a coiled worm that is being cut along its longitudinal axis while making a slide. The bottom image shows how the worm would appear if you are only looking at the part that was cut and put on a slide.



Thanks to everyone who wrote in with the answer for this case!

Case of the Week 133

The following was seen in an unstained wet preparation of stool from a patient complaining of abdominal pain (400X original magnification). It measures 30 microns in diameter. (CLICK ON IMAGE TO ENLARGE)



Identification?
What is a serious complication of infection with this organism?

Answer to Case 133

Answer: Taenia spp. ovum

I also asked "What is a serious complication of infection with this organism?"

Neuro Nurse answered this very well with the following:

"Cysticercosis results from ingesting T. solium eggs. Neurocysticercosis is the most common cause of seizure disorder in South and Central America.

Passing Taenia eggs in stool is indicative of tapeworm infection from eating meat with encysted larvae. Individuals passing T. solium eggs may infect themselves and others, causing outbreaks of cysticercosis.

Eggs of Echinococcus spp. are indistinguishable from those ofTaenia spp., but humans are intermediate hosts and do not pass Echinococcus eggs in stool."

I couldn't have said it better myself! Nice Job.

I will just comment that one cannot differentiate the eggs of T. solium (which may cause cysticercosis in humans) from the eggs of T. saginata (which does NOT cause human cysticercosis). Both eggs are small (approximately 30 microns in diameter), have a classic thick wall with radial striations, and may demonstrate internal hooklets (not well appreciated in this case).

The only way to definitively distinguish the T. solium from T. saginata is by examination of the gravid proglottids or scolex, since each have characteristic morphologic features. Epidemiologic features, such as history of eating undercooked pork or beef may also be helpful to determine which parasite is more likely to cause the infection.