Electron microscopic study on the development of Babesia ovis (Piroplasmia) in the salivary glands of the vector tick Rhipicephalus bursa.

The formation of Babesia ovis sporozoites in salivary gland cells of the vector tick Rhipicephalus bursa was studied by electron microscopy. The kinetics of B. ovis were found lying intracellularly on the second day after infestation (a.i.) of the ticks. The parasites enlarged rapidly losing all features of the motile form. Invaginations of the cell membrane initiated a fragmentation of this developmental stage. On the third day a.i the parasite (measuring 40 x 25 microns) was divided into numerous single membrane-bounded cytomeres, each provided with at least one lobed nucleus. On the fourth day a.i. sporozoite differentiation started at the periphery of the cytomeres, indicated by the appearance of several pellicle-bounded, exogenous protrusions into each of which a small portion of the nucleus was incorporated. Since the cytomeres lay very close together this differentiation occurred more by segmentation than by budding. Rhoptries and the so-called spherical body appeared in this developmental phase. Finally, the isolated, immature sporozoites lay in a granular matrix which contained remnants of the host cell cytoplasm. On the fifth day a.i. the sporozoites were fully developed, typically pear-shaped (2.8 x 1.2 microns) and provided with all characteristic structures of the invasive form.--This reproduction was compared to similar processes in other species of the Piroplasmia and the Haemosporina.