Testing of candidate acaricides in target animals (cattle) is expensive and requires large amounts of test compounds, and in order to increase the predictive nature of in vitro acaricide assays, robust surrogate animal models, with minimal compound requirements, are used. The objectives of these studies were to generate a rat acaricide test, characterize this new assay, and demonstrate the relationships for known acaricides tested in an in vitro assay (tick larval immersion microassay) to the activities observed in the Rat Acaricide Test. The Rat Acaricide Test (RAT) requires adult female rats, the nymph stage of Amblyomma americanum, and a new tick containment device. Compound efficacies were determined by measuring tick mortality or tick mass. Results with this assay demonstrated efficacy with the known acaricides tested and the dose-response relationships for each acaricide were determined. EC50 measurements for tick mortality for the acaricides tested ranged from 0.00011 to 0.085 mg/cm2. The rank order of potency for tick mortality in the RAT was fipronil> ivermectin> permethrin=chlorpyrifos, while the rank order of potency in-vitro was permethrin=fipronil> chlorpyrifos> ivermectin, demonstrating comparative potency differences between the in vitro and in vivo assays. In addition, the EC50 measurements for tick mortality and tick mass coincided for the acaricides tested, except for ivermectin, suggesting that RAT also detects toxic effect differences in tick feeding and tick mortalities. In summary, a Rat Acaricide Test has been created and characterized and together with the in vitro acaricide assay can be used for the identification of novel acaricides.
Species 1: Acari Ixodidae Amblyomma americanum (Lone Star Tick)
Keywords: Acaricide, Surrogate Animal Model
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