| Trypanosoma evansi is sharing some characteristics with T. brucei brucei and more |
| generally with the subgenus Trypanozoon, such as the nucleic DNA [27], morphology and |
| morphometry of the blood stage parasite (especially slender forms: small subterminal |
| kinetoplast, thin posterior extremity, large undulating membrane, free flagellum, thin and |
| long parasite, central nucleus, etc.) [1], and ability for peroral and mechanical transmission |
| [9]. However, the effects of T. b. brucei have not been observed in some hosts due to their |
| absence from its geographical distribution, limited to the tsetse belt (e.g., the effect |
| of T. b. brucei on water buffalos is not known); thus, comparison is not always possible. |
| T. evansi and T. equiperdum are different from T. b. brucei since they suffer from a mutation |
| leading to the homogenization of their kinetoplastic minicircles, which make them unable |
| to properly edit their mitochondrial RNA; for this reason, they are unable to transform into |
| procyclic stage, thus to implement a cycle in tsetse flies; they are consequently locked into |
| the host as a blood stream form [27]; they are also unable to recombine their DNA since |
| this event occurs during the implementation of the cycle in the tsetse fly [54]. |
| Distinct from T. equiperdum, T. evansi lost the kinetoplastic maxicircles, although the |
| extent of the loss is still under discussion since some part of the maxicircle DNA may be |
| remaining as shown in a Venezuelan strains [72]. |
| Transformation into stumpy form, which is observed in T. brucei spp. when preparing to |
| the implementation of the cycle in the vector, became useless in T. evansi and T. |
| equiperdum, which most probably contribute to the rarefaction of the stumpy forms of |
| these parasites, thus predominantly found under the slender form (only very occasional |
| stumpy forms have been described [1]). In addition to this modification, the loss of |
| kinetoplastic DNA can be partial (dyskinetoplastic: Dk) or total (akinetoplastic: Ak). |
| Finally T. evansi is a parasite derived from T. brucei by deletion of mitochondrial DNA |
| (kinetoplastic DNA) leading to a strictly blood form parasite, morphologically monotonous, |
| dividing by binary fission in the blood of numerous hosts. Mechanical vectors most |
| probably selected the most prolific parasites in given hosts, leading to some divergence |
| among the strains; however this aspect will be discussed elsewhere, in a paper devoted |
| more extensively to the transmission of T. evansi. Additionally, distinction between T. |
| evansi and T. equiperdum would also be discussed based on the tropism of the latter for |
| genital apparatus, which trapped it in a given host, equines, due to a predominant sexual |
| transmission. |
