Maximizing Theileria parva Sporozoite Maturation in Adult Male and Female Rhipicephalus appendiculatus by Varying Tick Age and Feeding Conditions: In Vitro Studies

Abstract

In vitro infectivity assays were carried out to determine the optimal conditions for stimulating Theileria parva sporozoite development in male and female Rhipicephalus appendiculatus. The conditions investigated were the interval between nymphal repletion and feeding of adults; feeding on rabbits for four days; incubation (at 37°C, 85% relative humidity) for 2 days followed by feeding on rabbits for 3 days or incubation for 6 days.  The ticks were dissected and their salivary glands homogenized to provide sporozoite suspensions for in vitro titration assays. Feeding of ticks on rabbits for 4 days produced significantly n1ore sporozoites in females than males (P= 0.010). However, male ticks incubated prior to feeding produced significantly more sporozoites than males fed on rabbits for 4 days (P=0.023). When the ticks were incubated prior to feeding there was no significant difference between the males and females (P= 0.125). Similarly, there was no significant difference between female ticks fed without incubation and those incubated prior to feeding (P= 0.625). Whether the ticks were incubated prior to feeding or fed without incubation, maximal titre were observed at 35 days after repletion as nymphs and a significant decline noted at day 42 with the exception of females (P= 0.021). Incubation for 6 days without feeding produced very low titre, and infective sporozoites were only detected when the ticks were tested 35 days after repletion. At 28 and 42 days, yields were low and the sporozoites were not infective to lymphocytes