Sunday, May 25, 2008

Case of the Week 23

The following worm was extracted during endoscopy, where numerous similar worms were seen attached to the large intestinal mucosa. The worm measures approximately 40 mm. CLICK ON IMAGE TO ENLARGE.

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

Answer to Case 23

Answer: Whipworm (a.k.a. Trichuris trichuria)

Note the small head wrapped around the body. The size and location are also important clues.
Good job Alasdair and Heather!

Monday, May 19, 2008

Case of the Week 22

Alex made the following movie for me, based on some footage I took during my daily commute. Caution: contains music; Turn your speakers either up or down!

Questions based on the movie:
1. List 5 infectious diseases spread by mice.
2. Mice can act as reservoirs for which parasitic infections?

Answer to Case 22

I had specified 'mice' for this week's questions, but I should have generalized it to rodents, since there is considerable overlap among the various disease-carrying species.

Tom made a great start in answering the questions. I will elaborate below. Keep in mind, this is just a list of the more common diseases - there are many more!

1. List 5 infectious diseases spread by rodents:
Tom says:
1. and 2. Rat bite fever (Streptobacillus moniliformis, Spirillum minor)
3. Hanta virus
4. Lymphocytic choriomeningitis
5. Plague & Leptospira
6. heebie jeepies (right Pritish?)

Here are some other diseases:
Lassa fever, Argentine hemorrhagic fever, Venezuelan hemorrhagic fever, hemorrhagic fever with renal syndrome, Venezuelan equine encephalitis, and tick-borne encephalitis.

Rocky mountain spotted fever, Boutonneuse fever, scrub typhus, murine typhus, tick-borne relapsing fever, Lyme disease, and salmonellosis (with S. typhimurium)

2. Rodents can act as reservoirs for which parasitic infections?:

Toxoplasma gondii (named after the African rodent it was first described in, Ctenodactylus gundi)
Chagas disease
Cutaneous and visceral leishmaniasis
(E. multilocularis and E. vogeli)
Schistosomiasis (with S. japonicum)
Hymenolepsis (Both H. nana and H. diminuta)

Tom also gave us the following:
"Just remember, these rhyming species carry lots of nasties: rats, bats, & cats (not sure about wombats...)" Although, 'man's best friend' doesn't get off the hook either - more on this in a future case of the week...

It is important to note that rodents can spread disease in a number of ways: the infectious organism can be excreted in urine and then be inhaled following aerosolization (e.g. Hanta virus) or ingested (e.g. Leptospirosis), or the organism can be directly inoculated through a bite (e.g. rat bite fever). Vectors can also be involved such as fleas, ticks, mites, mosquitoes, sand flies, and reduviid bugs. Finally, rodents may harbor a stage of the disease that is not directly infectious to humans and must first be transmitted to another non-human host (e.g. echinococcosis).

Sunday, May 11, 2008

Case of the Week 21

Did you know you can leave a message using the 'anonymous' feature? Feel free to leave a comment!

The following cyst is seen in this iodine stained wet-preparation from stool. It measures 16 microns in diameter.

What is the significance of finding this organism in this sample?

Answer to Case 21

Answer: Entamoeba coli cyst
The distinguishing features are the size (greater than 15 microns, although smaller immature forms may be seen), and most importantly, the number of nuclei (>4).

Significance to host: Tom said it well "Finding this organism means that the person was potentially exposed to less-than-ideal sanitary conditions at some point, and could be at risk for other pathogens passed under said conditions. This E. coli is probably not causing any damage to the host, and hence would not be considered a pathogen."

I particularly like Patty's comment:
OMG! I know this one! I agree with everything Tom said above and I'm thrilled that you gave us an easy one this week.

Actually, looking at iodine stained wet preps can be quite challenging, so Good job everyone!

Sunday, May 4, 2008

Case of the Week 20

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The following histologic sections were taken at autopsy from the brain (cerebral cortex) of a patient with cancer. Many foreign objects are noted in the first image (taken at 500x original magnification; the most obvious ones are marked with arrows). The second image (1000x) nicely demonstrates the 2 different forms of the organism which range from 10 - 15 microns (marked with arrowheads). CLICK ON THE IMAGES TO ENLARGE.


Answer to Case 20

Diagnosis: Acanthamoeba spp. encephalitis. This is a subacute disease that occurs mainly in immunocompromised patients, (such as in this case).

Diagnosis can be made from these 2 H&E images by identifying the classic cysts and trophozoites of Acanthamoeba spp. They are typically found clustered around blood vessels, consistent with the hematogenous route of entry to the brain. Note that these double-walled cysts are classic for Acanthamoeba spp., with a wrinkled or stellate outer cyst wall and smooth to slightly irregular inner cyst wall.

Your primary differential diagnosis in this case is infection with Balamuthia mandrillaris. Like Acanthamoeba spp., this ameba causes subacute meningoencephalitis in immunocompromised patients and results in cysts and trophozoites in the brain around blood vessels. However, the cysts have a much thicker outer cell wall than those of Acanthamoeba spp.

Finally, the ameba Naegleria fowleri can also cause human disease. Unlike the 2 amebae mentioned previously, N. fowleri causes fulminant and often fatal meningitis in previously healthy individuals. The 'typical' patient is a child who had recent contact with warm fresh water lakes. The route to the brain is not hematogenous; instead, amebae enter the nose with contaminated water and directly penetrate the cribiform plate. Cysts are NOT seen with Naegleria fowleri infection; instead, only trophozoite are seen in the leptomeninges.