Sunday, January 23, 2011

Answer to Case 147

Answer: Trypanosoma brucei trypomastigotes

Given the history that this patient is from Eastern Africa, this organism is most likely to be T. brucei rhodesiense, which is limited in distribution to the Eastern side of the continent. However, as "Anonymous" mentioned in a comment to this case, the 2 T. brucei subspecies, T. brucei rhodesiense and T. b. gambiense, cannot be distinguished by morphology alone. Neuro_Nurse correctly points out that knowing the geographic exposure of the patient is very important for determining the most likely causative subspecies, since there is currently no geographic overlap between the two. Uganda is the only country in which both subspecies are found, and they currently occupy separate regions of the country. Clinically, infection with T. brucei rhodesience is typically more virulent and is treated with different anti-parasitic agents than infection with T. brucei gambiense.

Based on the blood smear morphology, a similar appearing trypanosome, T. cruzi, should also be considered in the differential. T. cruzi is found in South and Central America and causes American trypanosomiasis (a.k.a. Chagas disease). The most reliable method for differentiating the trypomastigotes (motile blood stage forms) of T. brucei and T. cruzi is by the size of the kinetoplast (see below, arrows). T. brucei has a relatively small kinetoplast, while T. cruzi has a larger kinetoplast. T. cruzi trypomastigotes also commonly form a "C" shape, although this is a less reliable feature. Finally, T. cruzi may also be found as a non-motile amastigote form in various tissues, while T. brucei is only found in the trypomastigote form in humans.


Anonymous said...

Another useful distinction between T. brucei and T. cruzi is the presence of dividing forms in the blood in T brucei but not in T cruzi.

Charlie 103 said...

Sometimes I have found that you can also verify T.cruzi by the associated vector of either sandfly and/or triatomine (rhodius prolixus)