Preventing
tick bites is a fundamental step towards reducing the impact of tick-borne protozoal, bacterial and
viral diseases (
TBDs) in humans and animals. The aim of this study was to evaluate the efficacy of a combination of
imidacloprid 10%/
permethrin 50% and of
fipronil 10%/S-
methoprene 12% against ticks in naturally infected dogs and to assess methodological parameters to calculate
drug efficacy on tick immature stages. From July to August 2004, 45 privately owned dogs of various sexes, ages, breeds, coat length and habits were enrolled in a trial carried out in an area (radius approximately 50km) in Southern Italy. Three homogeneous groups (both for dog population and tick population) were formed: 15 dogs treated with
imidacloprid 10% and
permethrin 50% spot-on (group A), 15 dogs treated with
fipronil 10% and
methoprene 12% spot-on (group B) and 15 untreated dogs (group C). The dogs in each group were then sub-grouped according to their age and weight. Two different treatments were administered (time 0 and +28 days) to groups A and B, and the dogs were checked weekly for
tick infestation until day +56 post-treatment (p.t.). Twenty-four areas distributed on the whole body surface were examined for ticks at each follow-up, while only at time 0 and at day +56 p.t., ticks were collected from the dogs and identified. For the immature stages a semi-quantitative method was adopted and the load of immature stages was evaluated and grouped into four classes up to day +56 p.t. when the mean number of immature ticks (MIT) for each
infection class was evaluated. All the adult ticks collected were identified as brown dog ticks (Rhipicephalus sanguineus). Immature stages were first compared at day +28 p.t.. The efficacy of both products used in groups A and B on adult ticks was high and generally very similar. Conversely, the efficacy of
imidacloprid 10% and
permethrin 50% against immatures was higher than that of
fipronil 10% and
methoprene 12% throughout the observation period with statistically significant differences (p<0.05) at day +28 p.t. (i.e. group A=98.52%, group B=72.40%). On the whole, in analysing the efficacy of both products against adult plus immature ticks, it was found that the combination of
imidacloprid 10% and
permethrin 50% was more effective than
fipronil 10% and
methoprene 12%, with the differences being statistically significant at day +28 p.t. (group A=98.43%, group B=77.56%).