Answer to Case 538

Answer to Parasite Case of the Week 538: Toxocara species
Another case with lots of great discussion! There was quite a bit of debate on whether or not this was T. cati vs. T. leonina. This differentiation is potentially important since the former is commonly associated with human larva migrans (visceral, ocular and neural), whereas the latter only rarely is. As noted by Old One, a number of morphologic characteristics can be used to differentiate between the two, including the worm size, male spicule morphology, egg morphology and shape of the cervical alae. The cervical alae are short and wide in T. cati, and long and narrow in T. leonina. As the cervical alae in this case also appeared to be long and narrow, several readers were favoring T. leonina. However, the angle of the photographs made it difficult to really characterize the alae. Thus Old one suggested that we look at the eggs. Therefore, here is a new photograph for your consideration:

The scalebar represents 50 µm, putting the egg at ~70 µm long, within the size range of both species. Importantly, it has a pitted shell which is characteristic of T. cati. In comparison, the shell of T. leonina is smooth. Thus we have a nice case here of Toxocara cati! Mystery solved 😊.

This discussion still doesn't address Idzi's follow up question of what potential risk is posed to humans from contact with the infected cat and these worms. The adult worms themselves are not a risk to humans, but mature eggs, if ingested, can hatch to release larvae that cause larva migrans. While we clearly have at least 1 gravid female here, it is important to note that the eggs are shed in an unembryonated state and need to mature in the environment for 4 or more days (longer at lower temperatures) before becoming infectious to humans. Therefore, there is no immediate risk to humans in this case. However, eggs that may have been shed into the environment from the infected cat MAY pose a risk if accidentally ingested. Thus I would recommend carefully cleaning the litter box (wearing gloves, followed by meticulous hand washing) and getting the cat treated asap! As always, hand washing after soil contact (e.g. gardening) is also prudent.

Thank you all for the great comments!

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Case of the Week 537

This week's case comes from my lab with photos and video taken by Emily Fernholz. The objects shown were seen in a liver cyst aspirate. Identification?

Low power view (4x objective):

40x objective:

Here's a fun 'bird's eye' view (hit the play button twice):

Answer to Case 537

Answer to Case of the Week 537: Echinococcus species

Shown here are the classic protoscoleces of Echinococcus, each with a rostellum containing a row of hooklets (i.e. an 'armed' rostellum). The rostellum is the anterior protrusion found on some tapeworms.

As Old One mentioned, "There are 4 species of Echinococcus that infect humans: E. granulosus, E. multilocularis, E. vogeli, and E. oligarthus. Without more information such as host location, medical imaging, measurement of rostellar hooklets, one cannot be certain of the species. However one can make an educated guess.

E. multilocularis cysts are [usually] sterile (no protoscoleces) [in humans], E. oligarthus is exceedingly rare in humans, E. vogeli photoscoleces contain very few calcareous corpuscles, leaving E. granulosus as the best guess."  I will also add that infections with E. oligarthus or E. vogeli are extremely uncommon in humans and occur in Central and South America. E. granulosus is, by far, the most common species causing human infection in the United States, and causes a form of disease called cystic echinococcus. Usually a single cyst is produced, within which multiple daughter cysts may develop. In comparison, E. multilocularis causes alveolar echinococcus which infiltrates normal host tissue without remaining confined to a single cyst.

I did not provide enough clinical or epidemiologic information to provide a species level ID. However, in this case, we also believe that E. granulosus was the most likely identification.

Case of the Week 536

I have a fun case for you this week, donated by Dr. Richard Davis, Blaine A. Mathison, and Dr. Marc R. Couturier from ARUP Laboratories and the University of Utah School of Medicine.

The following objects were found in stool of a toddler living in the Oceania region. There were motile and described as "rice like".

Manipulation of the object and microscopic examination of the expressed material revealed the following structures measuring approximately 200 µm in diameter with a dark center. Within the dark area were numerous smaller objects measuring 25-35 µm in diameter:

Identification?

Answer to Case 536

Answer: Raillientina species, a parasite primarily of rodents and poultry. Kudos to Idzi for mentioning this in his differential!

As many noted, this parasite bears a striking resemblance to Dipylidium caninum, with production of small 'rice grain' like proglottids (which may be motile in freshly-passed stool) and collections of eggs - each containing a hooked larva.

This was definitely a challenging case. I didn't provide a high power view of the proglottid. If I had, you would have noted that it only had a single lateral or dorsal uterine pore (depending on the species) rather than the two lateral pores - one on each side - of D. caninum. 

Another feature that allows differentiation of this parasite from D. caninum is the presence of dark-centered eggs capsules rather than egg packets. Egg capsules are a characteristic of cestodes in the genera Inermicapsifer and Raillietina. They measure 100-200 micrometers in diameter and contain 1-12 eggs, each containing a hooked larva.

Differentiation of Inermicapsifer and Raillietina is achieved by examing the scolex; Raillietina has an 'armed' scolex (containing hooklets), while Inermicapsifer has an unarmed scolex. Unfortunately the scolex was not recovered in this case - it is rarely recovered from humans - and so morphology alone could not be used to differentiate the 2 cestodes. However, Richard, Blaine and Mark were able to exclude Inermicapsifer in this case due to the location of the patient and lack of travel history. You can read more about this case HERE.

Case of the Week 535

This week's case is by our awesome dermatopathology fellow and former chief resident, Kabeer Shah. The following was seen in a scraping of a papule from a patient with rosacea. Identification?

Check out the way this little guy moves!

Answer to Case 535

Answer to Parasite Case of the Week 535: Demodex sp. mite

There are two described Demodex species that are parasites of humans: D. folliculorum and D. brevis. They are characteristically differentiated by their location on the host and the length of their body. Demodex folliculorum lives in hair follicles and has a long opisthosoma (abdomen/posterior end), whereas D. brevis lives in sebaceous glands attached to hair follicles and has a shorter opisthosoma. Molecular analysis (e.g. using 16S rDNA) can also be used to differentiate the two species, and generally correlate with the morphology-based identifications.

Here is a general overview of the Demodex body segments:

Some of you wrote in trying to guess which of the two species is represented in this case. Unfortunately, the features aren't clear cut, and so we will have to call this simply Demodex sp.

Now here's a poem by Blaine:

So many people think they live immaculate lives

but among their hair follicles another creature thrives

you can shower and scrub to your heart's content

but all that effort won't make a dent

because the mite Demodex folliculorum continues to survive

Case of the Week 534

It's time for our fun monthly case from Idzi Potters and the Institute of Tropical Medicine, Antwerp. The following objects were seen in a stool specimen (direct wet prep) from a child with watery diarrhea. The objects measure approximately 40-45 µm in length. Identification?

Answer to Case 534

Answer to Parasite Case of the Week 534: Not a parasite; plant material. This is a neat finding since these structures (guard cells with stomatal pores) might be mistaken for parasite eggs such as Hymenolepis nana  due to their large size and morphologic features.

A quick biology review:
Guard cells are really neat. They are specialized cells in the epidermis of leaves and other parts of the plants that control gas exchange with the environment.They are produced in pairs and have a central opening called a stomatal pore. When a pair of guard cells are swollen (turgid) with water, the stomatal pore opens allowing carbon dioxide to flow in and oxygen (produced through photosynthesis) to flow out. While this gas exchange is essential to the plant, water is also lost through the stomatal pore; thus the plant has to balance the amount of CO2 absorbed from the environment with the amount of water lost through the pores.

Mary Parker kindly contributed the following image of stomata from the lower surface of an ash leaf and mentioned that "in a fresh sample as in the image, the plastids would contain greenish chlorophyll, but after gut transit, this would be lost."

Very cool! Thank you Mary!