Parasite Case of the Week 542

This week's case is a lovely gif image compiled by our excellent parasitology technical specialist, Heather Arguello. The following structures were seen on a non-nutrient agar culture that had been inoculated with corneal scrapings. The plate had been overlain with Escherichia coli to provide a food source for parasites that may be present in the specimen. The central structure is ~40 micrometers in maximum dimension, while the rounded structure to the left is ~15 micrometers in diameter. Identification?

Answer to Case 542

Answer to Parasite Case of the Week 542: Acanthamoeba sp. trophozoite and cysts

The free-living amebae, Acanthamoeba species and Naegleria fowleri (but not Balamuthia mandrillaris) can be grown on non-nutrient agar overlain with bacteria to provide a food source for the organisms. In this case, the presence of a characteristic double-walled cyst and trophozoite, along with the source (corneal scrapings) allow us to identify this ameba as an Acanthamoeba species.

We sadly did away with our free-living amebae culture a while back and replaced it with a multiplex real-time PCR assay. It's faster than culture, while providing equal sensitivity, so it is better for patient care. However, I do miss seeing these cool organisms grow in culture!

Case of the Week 541

This week's case was generously donated by Drs. Mauro Saio and David Hamer. The patient is a middle-aged male who noted the following objects in his stool. Individually, they measured approximately 1 cm in length. Identification?

 

Answer to Case 541

Answer to Parasite Case of the Week 541: not a parasite; citrus juice vesicles.

This is a not-uncommon finding in stool that is helpful to recognize, since it is occasionally submitted as a potential parasite. In this case, the patient reported eating clementines regularly. So here is a dissection of a clementine for comparison:

Pretty good, huh? Of course it's not possible to recognize the type of citrus from this case alone, and a report of "not a human parasite" is usually sufficient for patient care.

Wikipedia has a nice article on juice vesicles if you would like more information.

Case of the Week 540

This week's beautiful photographs are from Emily Fernholz at my lab. These objects were seen in a human stool specimen and measure approximately 80 micrometers in length. Identification?

The features are nicely appreciated on this video:

Answer to Case of the Week 540

Answer to Parasite Case of the Week 540: Macracanthorhynchus species, one of the acanthocephala ("thorny-headed worms"). M. hirudinaceus or M. ingens would be the most likely culprits, although as mentioned by Florida Fan, we would need the head of the worm to morphologically identify this to the species level. The acanthocephala are common parasites of animals, but only rarely infect humans. Infection is acquired through ingestion of an infected arthropod such as a millipede or beetle.

The eggs are very striking. They are ovoid and measure 80-100 micrometers in length. As described by Bernardino Rocha, they are dark brown egg with a thick rugged textured shell. Within the egg is the characteristic larval form (acanthor) with rostellar hooks (which you can sort of make out in this egg).

Interestingly, Macracanthorhynchus eggs are rarely seen in human stool. Blaine Mathison mentioned that this worm can occasionally reach sexual maturity in the human host and can even produce mature eggs; for some reason, however, the eggs are either not readily shed from the female, or are shed in such low numbers that they aren't commonly seen. Blaine also speculated that the eggs could be missed in O&P exams due to lack of technologist familiarity with them. Finally, there is the possibility of spurious passage from ingestion of soil or pig intestines containing the eggs/worms.

Of note, this particular patient had a follow-up specimen several days later which still contained Macracanthorhynchus eggs. Thus, my hypothesis is that this represents true infection rather than spurious passage.

Case of the Week 539

This week's beautiful case was donated by Florida Fan - a finding in a concentrated stool specimen:

The scale bars each represent 2.5 micrometers.
Identification?

Answer to Case 539

Answer to Parasite Case of the Week 539: Hymenolepis nana

This beautiful egg donated by Florida Fan nicely demonstrates all of the classic features of H. nana, including the thin inner membrane surrounding the hooked oncosphere [*] from which polar filaments arise. The polar filaments arise from opposite poles of the inner membrane (arrows) and spread out into the space between the inner and outer membranes, thus providing a key differentiating feature from the filamentless-Hymenolepis diminuta.

Blaine wrote a poem for this parasite back when I featured it in 2013. Here it is again for your enjoyment:

There once was a kid from Indiana

Who with his oatmeal did like banana

But with his food he did eat

A most wonderful treat

The cestode known as Hymenolepis nana

If you google "oatmeal" and "bugs," you will find multiple consumer complaints (and some nice YouTube videos) to explain the oatmeal reference!

Case of the Week 538

Here is our fun monthly case from Idzi Potters and the Institute of Tropical Medicine, Antwerp:
Your boss brings in some wormy things and mentions that “his cat regurgitated these in the morning”.
What is your diagnosis? Risk for humans?

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!