Cameline trypanosomosis (Surra) caused by
Trypanosoma evansi is considered the most serious disease affecting camels causing morbidity of up to 30% and mortality of around 3%
(Enwezor and Sackey, 2005;
Diall et al., 2022). Hilali et al., (2010) showed that the epimastigote stage reported in
titillator is related serologically and molecularly to
T.
evansi. This study is the first ultrastructural description of the epimastigote stage reported from the larval fluid of 2
nd stage larvae obtained from camels infected with
T.
evansi.
The epimastigote stage was found in the middle and posterior midgut of
C.
titillator 2
nd stage larvae. They were located close to the microvilli and in the lumen of the midgut (Fig 1).
The epimastigote was always observed in a dividing state with the peritrophic membrane of the midgut surrounding these stages (Fig 2).
The dimensions of the epimastigote stage varied from 4.5 to 20 µm × 1.11 to 2.5 µm (average 8.9 × 1.9 µm). The dimensions of the epimastigote reported here were shorter than those previously recorded in
C.
titillator larval fluid
(Hilali and Fahmy, 1993). This could be due to the use of glutaraldehyde as a fixative in this study and/or the ultrathin sections usually do not give the full length of the organism. The ultrastructure of the epimastigote stage showed that it was elongated fusiform in shape (Fig 3), enclosed in a unit plasma membrane (pellicle) formed of an outer thin and inner thick layer. Beneath this membrane lies a palisade of longitudinally arranged microtubules (Fig 5).
The nucleus was enclosed by a double-layer nuclear envelope (Fig 6). It contained an osmiophilic mass at its center, representing the nucleolus and a few peripheral dense masses. The flagellar pocket was in front of the nucleus (Fig 3 and 7).
Some of the flagellar pockets contained coated vesicles (Fig 7). These vesicles were also observed in the cytoplasm of some epimastigotes. A kinetoplast was rarely observed near the flagellar pocket (Fig 8).
Dyskinetoplastic forms were found in wild strains of trypanosome because of mutation or after treatment with trypanocides
(Hajduk, 1978). Long-term
in vitro cultivation of
T.
evansi resulted in dyskinetoplastic forms
(Zweygarth et al., 1990). The flagellum originates from inside the flagellar pocket and extends anteriorly (Fig 7). A paraxial rod was observed within the flagellum (Fig 7). Thin-walled vacuoles and glycosomes were noticed in the cytoplasm while ribosomes were distributed throughout the matrix (Fig 4). Many dark spherical or oval osmophilic bodies were distributed in the cytoplasm (Fig 4). Thick-walled globular or oval-shaped vesicles were distributed in the cytoplasm, particularly at the posterior end (Fig 8). Poorly developed rough and smooth endoplasmic reticulum was observed in the cytoplasm. The Long-ramified mitochondria were present on the lateral sides of the epimastigote (Fig 4). In this study, the volume and activity of the mitochondria were high while the volume of the glycosomes varies the opposite. This agreed with
Lopes et al., (2010) who reported this finding in the midgut stages of
T.
brucei. The thick-walled triangular vacuole reported here in the cytoplasm near the nucleus probably represents degenerated flagellar pocket of a dying epimastigote (Fig 7).
