Sunday, May 31, 2020

Answer to Case 593

Answer to Parasite Case of the Week 593: Strongyloides fuelleborni

This fascinating zoonotic parasite is endemic to parts of sub-Saharan Africa and infects both human and non-human primates. It is likely under-reported, which may be due to the resemblance of its eggs to those of the hookworms. Unlike hookworm eggs which are shed in an unembryonated state, the eggs of S. fuelleborni typically contain fully-developed larvae.

Similar appearing eggs with larvae may also be seen with heavy infections with Strongyloides stercoralis; however, the eggs are seen in conjunction with larvae, and occasionally adult worms, which are not seen with S. fuelleborni cases. Here are a couple of past examples of S. stercoralis from my blog with adults, larvae and eggs:
Case 469 Question and Answer
Case 499

Idzi Potters and his colleagues suspected S. fuelleborni in this case based on the appearance of the eggs, and were later able to confirm the identity through sequencing of the 18S rRNA gene.

After leaving the specimen in the refrigerator for 5 days, Idzi was also able to observe larvae from the parasite including the following example:
You can read the whole report in his recent publication:

Thanks again to Idzi and the Institute of Tropical Medicine Antwerp for donating this case!

Monday, May 25, 2020

Case of the Week 592

This week's interesting case was donated by Drs. Lee Decollings and Dejan Nikolic. The patient is a middle-aged male with travel approximately 2 months ago to Ethiopia, Nigeria and Cameroon. In the past few years, he has also traveled broadly in sub-Saharan Africa, Asia and South America. He presented with fever and myalgias following a recent medical procedure.

Diagnosis? Where did he likely acquire this infection?

Sunday, May 24, 2020

Answer to Case 592

Answer to Parasite Case of the Week 592: Plasmodium malariae; likely recrudescent infection, given that he has been without symptoms for > 2 months since his last travel to sub-Saharan Africa. While P. knowlesi is also in the differential based on the morphologic overlap between P. knowlesi and P. vivax, the long period of time since his travel to SE Asia would be atypical for P. knowlesi infection.

Some of the classic P. malariae features seen in this case are the small size of the infected red blood cells, schizonts with only 6-12 merozoites, band forms, and a basket form:
A tip for those studying for boards - be sure you know the difference between recrudescence and relapse.

Recrudescence - seen primarily with P. malariae infection, but can also be seen with other Plasmodium species that lack hypnozoites.
Recrudescence refers to recurrence of infection. With P. malariae, recrudescence is thought to be due to the indolent growth of this parasite, enabling survival for many years, even with chloroquine treatment. Chloroquine is the drug of choice for P. malariae infections, and it is preferentially concentrated in the food vacuoles of metabolically active trophozoites. Here it binds to hematin and prevents its polymerization, resulting in oxidative stress to the parasite and eventual lysis. Given the low growth and metabolism of P. malariae asexual stages, some trophozoites can escape the action of chloroquine and later cause disease recrudescence. Recrudescence is different than relapse (see below) in that it doesn't result from activation of hypnozoites.

Relapse - seen with P. ovale and P. vivax infection.
Relapse is due to activation of dormant hypnozoites in the liver.

The final mystery in this case is the location in which the patient acquired infection. He had traveled to Ethiopia, Nigeria and Cameroon approximately 2 months prior to symptom onset, but according to the United States CDC, P. malariae is not found in appreciable amounts in these countries. What the CDC doesn't note in these lists, however, is that P. malariae is found throughout sub-Saharan Africa, and is present in all of the areas where P. falciparum is found. P. malariae is also found in parts of Asia and South America, so he could have acquired infection from many of his previous travels.

Thanks again to Drs. Decollings and Nikolic for donating this interesting case!

Monday, May 18, 2020

Case of the Week 591

This weeks case was generously donated by Dr. Michele Bloomer. The following object was removed from the eye socket of an adult patient. According to the surgeon, there were numerous similar-appearing objects present, but only 1 was submitted to the laboratory. About 1 month prior, the patient had undergone surgery to remove his eye as it was involved by a large cancerous growth that had extended from his eyelid.


Sunday, May 17, 2020

Answer to Case 591

Answer to Parasite Case of the Week 591: L3 larva of Phormia species

As Blaine mentioned, this is a case of facultative myiasis involving an existing wound. The wound was caused by removal of the eye due to a large cancerous growth. What I didn't share is that the growth had been neglected, and the wound may have been as well. Several of you mentioned that this is a third stage (L3) larva, which indicates that the larva was allowed to mature for sometime within the wound.

Although we can't see the tracheal trunks to say if they are pigmented or not, the posterior spiracular plate is clearly visualized and shows an incomplete peritreme, relatively-straight slits without lateral swellings, and slits are directed towards the region where the peritreme is incomplete, consistent with Phormia sp.

Some of you mentioned Lucilia sp. in the differential, although in my interpretation, Lucilia has a complete peritreme with distinct button, unlike what we are seeing here.

The CDC has freely-available pictorial keys online which are a useful starting place when examining fly larvae. Blaine and I also published a guide for Laboratory Identification of Arthropod Ectoparasites. If you don't have access to manuscript, send me an email and I can send you a copy for your own personal use.

Monday, May 11, 2020

Case of the Week 590

This week's fascinating case was donated by Dr. Graham Hickling. He captured the following scene that he entitled "Hatching". What are these newborns?
See them here LIVE (fast motion):

Sunday, May 10, 2020

Answer to Case 590

Answer to Parasite Case of the Week 590: Ixodes scapularis larvae, freshly hatched from an egg mass laid by a captive female. This fascinating video was generously donated by Dr. Graham Hickling who does research on hard tick biology.

While there isn't enough information present to specifically identify these ticks, you can say a few things about them from the video:
  1. The have only 6 legs, and are therefore larvae.
  2. In North America, the long mouth parts and ovoid body would be most consistent with Ixodes species. 
As astutely noted by Old One, "Six legs, newly hatched, long club shaped palps, apparently no visible festoons and no visible inverted U anal plate. Definitely newly hatched seed ticks (I would like to suggest a name change to TICK-ETTE) as in pick up your tickettes here. You might need to FLAG them down."

We've actually seen these little wonders before in a different blog post:
HERE is momma tick laying her eggs, with a video showing the action HERE. I HIGHLY recommend this video - it is fascinating! You may want to check out the other great videos on this site: Thanks again to Graham for sharing his 'babies' and passion for acarology with the rest of the world.

While I. scapularis tick larvae won't usually hatch until this summer, the nymphs that have over-wintered from last year are now out, so be sure to take precautions against tick bites when outdoors!

Monday, May 4, 2020

Case of the Week 589

Happy Monday everyone! It's our first Monday of the Month, and time for our monthly case from Idzi Potters and the Institute of Tropical Medicine, Antwerp.

The following objects were seen in an iron hematoxylin-stained stool preparation from an asymptomatic patient with frequent travels to Asia. The objects measure 10-20 micrometers in greatest dimension.


Sunday, May 3, 2020

Answer to Case 589

Answer to Parasite Case of the Week 589: Iodamoeba buetschlii cysts and trophozoites.

Note that the trophozoites and cysts have a single nucleus with a large, often eccentric, karyosome. Cysts characteristically have a large glycogen-filled cytoplasmic vacuole that is highlighted when using iodine on a wet mount preparation. The glycogen vacuole does not stain with trichrome or iron hematoxylin, and instead appears as an empty space as in this case:

This organism gets its genus name from its iodine staining property (iod + amoeba), whereas the species name honors the German protistologist, Johann Adam Otto B├╝tschli. Note that the term "buetschlii" is used when citing a formal scientific name rather than "b├╝tschlii" as per nomenclature standards.

Blaine pointed out there there were also some Blastocystis along for the ride (or vice versa):
 Old One also noted that the large vacuole looks a bit like a mask, which is a good reminder to wear a mask when going out in public to protect others around you.