Sunday, October 31, 2021

Answer to Case 659

Answer to the Parasite Case of the Week 659: Onchocerca volvulus adult worms and microfilarie. 

If you didn't already see it, check out the whole slide scanned image HERE.

In this case, you can see a large subcutaneous nodule containing the adult worms (each female with  a characteristic "double barrel" uterus) and microfilariae being released into the surrounding skin. 

The microfilariae are the primary source of disease, as they crawl through the skin causing intense itching and inflammatory changes. They also go to the eye and cause irreversible blindness. The latter is the reason that infection is called "River Blindness". Infection is transmitted through the bite of infected black flies (Simulium sp.) which breed in fast flowing waters.

Tuesday, October 26, 2021

Case of the Week 658

This week's case is a thick blood film from a patient with fever and recent travel to East Africa. Diagnosis? Would you like any additional studies?

Sunday, October 24, 2021

Answer to Case 658

Answer to the Parasite Case of the Week 658: Trypanosoma brucei

Given the travel history and rapid onset of symptoms, T. b. rhodesiense is the most likely parasite present. This case shows very high parasitemia with numerous trypomastigotes seen on the patient's thick blood film. Here is the corresponding thin blood film, highlighting some of the key diagnostic features:

Note that the motile flagellate form (i.e., the trypomastigote) of T. brucei divides by binary fission in the peripheral blood. This is in contrast to Trypanosoma cruzi, the cause of American trypanosomiasis (a.k.a. Chagas disease), in which it is the non-motile tissue amastigote form that divides. Amastigotes are not seen with T. brucei infection.  

When seen in the peripheral blood, the trypomastigotes of T. brucei need to be differentiated from those of T. cruzi - particularly when the travel history is not known. Humans can also have transient asymptomatic parasitemia with some of the zoonotic trypanosomes.

So what are the next steps? 
If there was a concern for mixed trypanosomiasis/malaria, then examination of a thin film (and/or PCR) would be indicated, as suggested by Murtadha Maradun Mohammad.

If we are uncertain of the infecting Trypanosoma subspecies (e.g., if the patient was in Uganda where both T. b. rhodesiense and T. b. gambiense are present), then we could also perform serology or PCR as noted by John Markantonis and Harsha Sheorey.

Importantly, LS noted that examination of the CSF would be the next step once we have confirmed the diagnosis, since detection of parasites in the CSF would change the treatment regimen. 

You can read about the treatment regime for early and late (CNS) stage Rhodesian trypanosomiasis HERE. The only approved therapy for late stage Rhodesian is melarsoprol, an arsenic-containing compound that causes encephalopathic reactions in 5–10% of patients. When this occurs, there is a ~50% case-fatality rate (!) 

Tuesday, October 19, 2021

Case of the Week 657

This week's case features a Giemsa-stained thin blood film from a patient with recent travel to India. Identification? For a BONUS, can you list the different stages in images 1-4 below?

Sunday, October 17, 2021

Answer to Case 657

 Answer to the Parasite Case of the Week 657: Plasmodium vivax

Thanks to all of the great comments on this case! There are so many classic features of P. vivax here, that it makes for a fabulous teaching slide. Florida Fan very nicely outlined all of the diagnostic features along with his thought process for coming to the final identification:

1/ The ring is fairly large, and the infected red cell is larger than the not infected. As such, there is a predilection for reticulocytes. Either P. vivax or P. ovale.

2/ The mature trophozoites are ameboid form, showing them to be highly Vivacious. More than likely P. vivax.

3/ The schizont in the third picture demonstrates more than twelve merozoites, P. ovale does not usually have that many. (on average, 8)

4/ The gametocyte in the fourth picture is not Falciform, it occupies almost the entire red cell. Though there is a little bit of fimbriation, all evidence gathered so far including the geographic area are consistent with an identification of P. vivax.

Here is a composite image of the 4 forms shown in this case:

Tuesday, October 5, 2021

Case of the Week 656

 It's time for our monthly case with Idzi Potters and the Institute of Tropical Medicine, Antwerp:

The following was seen in a urine sediment from a backpacker returning to Belgium following a 2-month's trip in Northern Senegal. During his travels, he reports being bitten by insects, drinking and eating local foods, and swimming in fresh water lakes. He is asymptomatic, but is concerned that he may has picked up a parasite along the way. 

How would you interpret this finding?

Monday, October 4, 2021

Answer to Case 656

 Answer to the Parasite Case of the Week 656: mite, probable contaminant from the environment. Not likely of human medical significance.

As several readers noted, this mite is not one of the 2 human pathogenic mites, Sarcoptes scabei or Demodex. Instead, it is likely a mite from the environment, such as Dermatophagoides, the dust mite. The presence of many squamous epithelial cells in the background would support this idea:

You can read the following posts for more information for how to differentiate the various mites found in human specimens:

Case of the Week 634: Free-living mite found in stool

Case of the Week 196: Differentiating Sarcoptes scabei from other mites

Case of the Week 601: Key identifying features of Sarcoptes scabei