Electron microscopic studies on the development of kinetes of Theileria parva Theiler, 1904 in the gut of the vector ticks Rhipicephalus appendiculatus Neumann, 1901.

The development of motile stages, called kinetes, from a stationary stage (regarded as zygote) has been followed in Theileria parva by means of electron miscroscopy. This process started after moult of the tick nymphs which had sucked on highly infected calves, i.e. about 20 days after repletion (a.r.) of the ticks. The transformation took place by formation of a growing protrusion (= anlage) into an inner, enlarging vacuole. During this process the limiting membrane of the enlarging vacuole serves as the outer membrane of the developing motile stage, whereas the two inner ones as well as the subpellicular microtubules are newly formed. This transformation proceeds rapidly, so that on the 25th day a.r. most of the kinetes have already left the gut cells and started penetration into the salivary gland cells. On the way to the salivary glands nuclear divisions occurred within the kinetes. The steps of the transformation described were compared to those in T. annulata and to ookinete formation in haemosporidia.