Control of induced infestations of three African multihost tick species with sustained-release ivermectin

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Abstract
The efficacy of ivermectin, released intraruminally from a 28-day-delivery device was evaluated in two titration studies against induced infestations of adultRhipicephalus appendiculatus, R. evertsi andHyalomma truncatum on cattle. Cattle were given a sufficient number of devices to release ivermectin at approximately 20, 40, 60 or 80 μg kg−1 day−1 at a steady-state rate 7–28 days after administration. Tick mortality was recorded, engorged female ticks were weighed and individually incubated, and reproductive data were recorded to determine a reproductive index for the species at various dose levels. Mortality of male and female ticks compared to that of controls was directly related to the daily dose of ivermectin, as was the number of ticks not engorging. Ticks fed on ivermectin-treated cattle had a smaller mass when engorged and laid smaller egg-masses, both absolutely and as a proportion of engorged mass. The index of reproduction ofR. appendiculatus was reduced by more than 99.9% at 20 μg kg−1 day−1, and the reproductive indices ofR. evertsi andH. truncatum were reduced by more than 99.9% at dose rates of 40 μg kg−1 day−1 and above. Practical implications of the application of sustained-release ivermectin for the control of multihost ticks and tick-borne diseases are discussed.