The effect of temperature on the rate of transmission of Theileria parva parva infection to cattle by its tick vector, Rhipicephalus appendiculatus

Abstract

A steer was infected with Theileria parva parva Kilae stabilate; nymphal Rhipicephalus appendiculatus ticks were applied to its ears so that they completed repletion when the steer had a high piroplasm parasitaemia. The engorged nymphs were subsequently incubated at 28 degrees C for 26-29 days to complete moulting, when the adult ticks were divided into two groups; one was incubated at 18 degrees C for 20 days and the other at 18 degrees C for 14 days and then at 37 degrees C for 6 days. Groups of ticks incubated at 37 and 18 degrees C were triturated and each resultant supernatant fluid inoculated into a steer. Both steers became infected, but the 37 degrees C supernatant group showed a much shorter pre-patent period to schizonts. Groups of ticks incubated at 37 or 18 degrees C were applied to pairs of cattle for 24, 48 and 72 h and then removed. There was a more rapid transmission of theileriosis to cattle by ticks kept at high ambient temperatures compared to those kept at low ambient temperatures. All cattle on which ticks treated at 37 degrees C were applied developed acute and fatal T. parva infection irrespective of the duration of tick application, while only 1 animal receiving ticks treated at 18 degrees C and fed for 72 h developed infection. The pre-patent period for macroschizonts was very short in all the groups receiving ticks incubated at 37 degrees C.