Sunday, June 29, 2025

Answer to Case 780

Answer to Parasite Case of the Week 780: Trypanosoma brucei trypomastigotes. 

As noted by Florida Fan, "This is definitely a case of trypanosomiasis. The flagellate doesn’t show a prominent kinetoplast nor assume a C shape in general. This rules out Chagas disease caused by T. cruzi. We have Trypanosoma brucei, yet morphology alone doesn’t warrant a differential diagnosis of subspecies gambiense nor rhodesiense." 

Idzi also noted that "In the first picture we can clearly see the difference between the two morphologies of T. brucei: the "short stumpy" form (adapted for survival in the tsetse fly vector --> transmission) versus the "long slender" form (which multiplies in the host)!" Here is an annotated version of this image showing these two morphologies:

I had also asked what additional information is needed in this case - and you all responded with excellent suggestions. In summary,  

  • We first, we need to know the travel history to determine the likely subspecies. PCR could also be performed. This is important for treatment and prognostic implications. 
  • Second, we need to know the stage of disease, as this will also drive treatment decisions. As noted by Idzi, "A lumbar puncture will be able to tell us if the patient has evolved to stage II of the disease, where the parasite has invaded the central nervous system. Even if no tryps are found in the CSF, a raised number of WBCs in the CSF will still be indicative of stage II disease (when tryps are found in the blood).
The WHO released updated treatment guidelines for Human African Trypanosomiasis (HAT). Treatment is complex and can have significant side effects. This is especially true for rhodesiense-HAT, in which intravenous suramin is used for first stage disease and melarsoprol, an arsenic derivate, is used for second stages disease. It's shocking that we are still using arsenic to treat infectious diseases. Melarsoprol has many adverse effects, including reactive encephalopathy which has a 3–10% fatality rate!

Getting back to this case: additional history revealed that the patient had been on a hunting trip to Zambia, and therefore we can infer that the patient has East African HAT caused by T. b. rhodesiense. Idzi predicted this, stating that "chances are very very big that this is T. b. rhodesiense because this is the subspecies that will get quickly to a parasitemia high enough to be able to detect the trypanosomes in a thin blood film." 

Many thanks again to Dr. Mutnal for donating this interesting case. 


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