177 | Efficacy of parasitic treatments in the brown dog tick (Rhipicephalus sanguineus): experimental evidence of acaricide resistance

Davide Pepe, Dario Bonomo, Vincenza Cannella, Annalisa Guercio, Santina Di Bella | Istituto Zooprofilattico Sperimentale della Sicilia “A Mirri”, Palermo, Italy.

Dog ticks represent an increasingly important health concern, both in veterinary medicine and from a public health perspective. Among these, the brown dog tick (Rhipicephalus sanguineus) is particularly widespread in urban and domestic environments and shows a strong capacity to adapt to anthropogenic conditions. This species plays a key epidemiological role as a vector of veterinary pathogens, such as Ehrlichia canis, and zoonotic agents, including microorganisms of the genus Rickettsia, with potential implications for human health. Control of dog tick infestations primarily relies on chemical parasiticides. In this context, fipronil and permethrin are among the most widely used active ingredients and are present in numerous commercial formulations for dogs and, in the case of fipronil, also for cats. Fipronil, a phenylpyrazole, acts on the nervous system of arthropods by interfering with nerve impulse transmission, while permethrin, a synthetic pyrethroid, exerts a rapid and persistent neurotoxic effect and is also used in environmental treatments. In this study, the efficacy of these two acaricides was evaluated using the Larval Packet Test (LPT), a FAO standardized method in which tick larvae are exposed to different concentrations of the active ingredient on impregnated filter papers, allowing assessment of larval mortality under controlled conditions. Each concentration was tested in triplicate, ensuring the reproducibility and reliability of the results. The results showed reduced sensitivity to fipronil and a marked decrease in permethrin efficacy, with significant larval survival even at concentrations commonly considered effective. These findings indicate the presence of acaricide resistance, particularly relevant for pyrethroids, highlighting that the efficacy of parasitic treatments can no longer be assumed. Overall, this study emphasizes the importance of an integrated and rational approach to dog tick control, based on monitoring the effectiveness of active ingredients, rational use of available products, and implementation of sustainable prevention strategies, in order to reduce the health risk associated with pathogen transmission and preserve the long-term efficacy of parasitic treatments.

The research was funded by the Italian Ministry of Health: IZSSI 03/23 RC.