Comparative infectivity for cattle of stabilates of Theileria lawrencei (Serengeti) derived from adult and nymphal ticks

Abstract

Larval and nymphal Rhipicephalus appendiculatus ticks were fed simultaneously on steers reacting to the inoculation of an infective stabilate of cattle-passaged Theileria lawrencei (Serengeti). The larvae and nymphs dropped engorged from the steers when their intra-erythrocytic piroplasm parasitaemias were in excess of 14 per cent.: after the ticks had moulted, they were fed on rabbits and removed after 3 and 5 days respectively. Some of the ticks were processed for histological examination of their salivary glands whilst others were ground and stabilates were prepared from them. Examination of the salivary glands indicated that there was a higher infection rate in the nymphs than in the adults although this was not statistically significant: subsequent inoculation into susceptible cattle of titrated aliquots of the stabilates, however, showed that aliquots from a certain number of adult ticks were more infective than those from the equivalent number of nymphal ticks. The duration of the prepatent period in the susceptible cattle could be correlated with the infective dose. The possibility of obtaining stabilates of nymphal material by feeding larval ticks all over the body of an infected animal is discussed, since such stabilates may be more concentrated and more easily prepared than adult tick stabilates.