Laboratory investigations on the effect of insecticides and host immunisation for control of tick infestation

Abstract

The thesis is in two parts. In the first, three species of economically important African ixodid ticks, Rhiplcephalus appendiculatus, Amblyomma hebraeum and Amblyomma variegatum were investigated for the first time for their susceptibility to three newly developed photostable synthetic pyrethroids with long residual activity, permethrin, cypermethrin and decamethrin. Results of tests on unfed larvae, unfed nymphs and unfed adult ticks using different methods of testing such as the immersion technique, dipping, impregnated packet technique, tea bag ” technique and topical application are presented, and the relative susceptibility of the different species and of different developmental stages to the three pyrethroids is compared. A limited number of experiments were also done on the effect of the compounds on engorged nymphal ticks. The potential of the synthetic pyrethroids in the control of multi-host tick ecto­parasites of animals in Africa is discussed. The second part of the thesis is concerned with investigations on acquired immunity or resistance in host animals to tick infestation and its role in tick infestation of animals. This was investigated by using small animal models, rabbits and guinea pigs, and four speciesof ixodid ticks, R. appendiculatus, A. hebraeum and A. variegatum and an European species, Dermacentor marginatus. The development of immunity in the animals following a primary infestation with one species of tick, to a second infestation with the same species, and of cross-immunity to a second species, were investigated. Sera from immune animals were tested by serological methods for antibodies to tick salivary gland antigens. In a limited series of experiments, infection of animals with blood pathogens and the injection of tick cell extracts and larval tick homogenates into animals were investigated for their effect on development of immunity to tick infestation. The role of chemical acaricides and of acquired host immunity as an alternative or additional method to chemical control in the overall strategy of tick management on animals is discussed in the light of results obtained from the investigations.