Test systems for tick repellents.

There is an interest in the development of repellents for personal protection of humans and animals against ticks. Evaluation of new substances or formulations needs adequate test procedures to show efficacy of the compounds. A variety of repellent assays for ticks are described in the literature. Available biotests can be grouped in three categories (i) use of live hosts, (ii) use of some kind of tick attractant associated with hosts, or (iii) no use of attractants at all. The latter are often better to standardize and are cheap, but suffer from a poor ability to filter out weak repellents. The former two are usually more predictive in terms of forecasting the efficacy of the product under practical conditions, although sometimes difficult to standardize, particularly in the field, but usually expensive and time consuming. Therefore, recent developments concentrated on laboratory assays like the Moving-object bioassay or the human volunteer test, allowing the tick to display its host-seeking behaviour as close as possible to that shown in nature, yet offering a standardized procedure.