Pathological effects and reduced survival in Rhipicephalus appendiculatus ticks infected with Theileria parva protozoa.

Pathological effects have been demonstrated in a number of arthropod species as a consequence of parasitic infection. This is usually manifest as reduced arthropod survival and/or fecundity. This paper describes the detrimental effects the protozoan parasite, Theileria parva has on Rhipicephalus appendiculatus ticks. R. appendiculatus ticks were dissected and sectioned at regular intervals during their nymph to adult moult after detaching from a T. parva infected calf, and assessed by light and electron microscopy. The reproductive capacity of the T. parva infected ticks was also compared with that of control, uninfected ticks. The number of T. parva forms seen during the ticks' moult were recorded and showed a substantial reduction as the moult progressed. A non-linear relationship between piroplasm ingestion by the engorged nymph and eventual adult salivary gland infection levels was shown. Tick gut and salivary gland pathology was noted at various stages throughout the moult and correlated with the parasite burdens in the affected organs at those timepoints. The reproductive performance of infected ticks was greatly impaired compared to controls. Infected female ticks had longer bloodmeal engorgement times, reduced bloodmeal volumes, smaller egg batch weights and greatly decreased egg hatching success. The pathological effects are discussed in relation to parasite population dynamics within the ticks and compared with similar examples of pathology evidenced with other parasite infected arthropod species.