Additive Efficiency of Fipronil + Methoprene Compared to Fipronil Alone against Rhipicephalus sanguineus Ticks in Naturally Infested Dogs

The acaricidal efficiency of fipronil alone and fipronil + methoprene compared to commercial fipronil and commercial fipronil + methoprene, applied by the epicutaneous route (spot-on) in dogs naturally infested with ticks, was assessed. Thirty dogs infested with high loads of ticks were used. On day 0, the dogs were divided into 5 groups of 6 animals each. Each animal was duly identified for individual and group monitoring. Treatments were made based on body weight according to manufacturer’s instructions. Group 1 (G1) received 10.0% fipronil at a single dose of a pipette applied by epicutaneous route in the base of the neck. G2 received 10% fipronil + 10% methoprene in single application similarly to G1. G3 was treated with 9.8% commercial fipronil as before mentioned. G4 received commercial 9.8% fipronil + 9.8% methoprene applied as in previous groups. G5 served as an infected untreated control. Animals were examined by thumb tick counts on days 0 (Treatment day), 3, 7, 14, 21 and 28. Efficacy was measured as a percentage of tick reduction in the treated groups relative to the untreated control. Results indicated an overall efficacy of 88.2%, 93%, 90.4% and 99.3%, respectively. There was no significant statistical difference between the treated groups (P < 0.05), neither in sex nor in weight. Engorged ticks were the most frequent, followed by the nymph group. However, by the end of the study these data were reversed due to the fact that only small larvae were found, which we interpreted came from engorged ticks that released their progeny before dying and a month later their offspring began to be observed presently and in full development. It is concluded that the combined formulations of fipronil + methoprene compared to fipronil applied alone, showed an additive effect against Rhipicephalus sanguineus ticks in naturally infested dogs kept in captivity.