Efficacy of the fipronil 10% + (S)-methoprene 9% combination against Rhipicephalus sanguineus in naturally infested dogs: Speed of kill, persistent efficacy on immature and adult stages and effect of water

This field trial was designed to test the efficacy, in terms of treatment and prevention, of the
fipronil 10% + (S)-methoprene 9% combination against immature and adult stages of
Rhipicephalus sanguineus in naturally infested dogs, and to assess the effect of a single plain
water exposure. Twenty-four dogs of various age, sex, weight and coat length were divided
into two homogeneous groups, treated (T) and control (C), and housed into twin outdoor
kennels. Trial baseline was designed as day 0, when dogs from group T were treated with a
commercial spot-on formulation of fipronil 10% + (S)-methoprene 9%, while subjects from
groupC were left untreated and served as control. After treatment, tick load for each included
dog was estimated, for both adult and immature ticks, using the localization and count over
the entire body surface at the following time-points: day 2, to evaluate the speed of kill and at
days 7, 14, 21 and 28 to assess the persistence of efficacy. The effect of water exposure on the
product efficacy was tested at day 14 of the study, when six dogs, homogenously selected
fromgroup T, were soaked through with plain water. The overall tick load in dogs fromgroup
C was high throughout the entire study period, ranging from 103.2 (day 28) to 161.3 (day 0),
and confirmed the high tick pressure. Speed of kill calculated at 48 h post-treatment was
slightly higher for adult ticks (96.2%) than for immature stages (91.6%). Compared to the
control, dogs treated with the fipronil + (S)-methoprene maintained a significantly lower
mean tick load for both adult and immature stages in the four weeks of observation.
Persistence of efficacy against immature stages ranged from 97.1% the first week, 99.6%
second week, 99.7 third week and 93.1% in the last week. In the same way, efficacy against
adult ticks was constantly high, shifting from 94.5% to 92.5%. Overall efficacy
(adults + immatures) was the strongest in the first two weeks (i.e., 96.1% and 96.6%) and
lowered in the two remaining weeks (i.e., 94.2% and 93.4%). Results showed that water
exposure did not affect the activity and persistence of the testedcombination.Onthe basis of
this field trial, the fipronil + (S)-methoprene combination represents a highly efficacious
product to control all stages of R. sanguineus ticks on dogs.