Figure 3. T. lewisi and T. evansi on a Giemsa-stained blood smear from a rat submitted to a mixed experimental infection (credit, Marc Desquesnes).

Smeared and stained in the same conditions, the parasites exhibit here their striking characteristics: the size of the kinetoplast (large in T. lewisi and small in T. evansi) is the most reliable criteria to distinguish these sub-genera; however, other characteristics can be observed, such as: the size of the parasite (T. lewisi>T. evansi), the nucleus position (central for T evansi, posterior for T. lewisi), the undulating membrane development (exhibiting regular waves in T. evansi and irregular ones in T. lewisi). Finally, an unusual feature can be observed on one specimen of T. lewisi with a very long posterior extremity, this morphotype use to be called “longicaudale” [1].