The brown dog tick (Rhipicephalus sanguineus) is a widespread blood-feeding parasite of dogs. The species is considered as a vector of Crimean-Congo hemorrhagic fever virus and Rickettsiae. In dogs, it can transmit pathogens responsible for severe diseases: bacteria such as Ehrlichia canis, Ehrlichia ewingii (can be transmitted to humans); protozoa such as Hepatozoon canis, and helminths such as Cercopithifilaria. These microorganisms are mostly transmitted after attachment during the blood-meal step. Rapid removal of already attached ticks and prevention of blood-feeding by this parasite are, therefore, two key points of the prevention strategy against ticks and their associated diseases. In order to achieve this aim, dogs can be treated topically and on a regular basis with different formulations of acaricidal products like fipronil or permethrin. The products currently available to veterinarians and pet owners vary not only regarding active ingredients and their concentrations, but also regarding their overall formulations. Chemistry and quality of ingredients confer to the products a large part of their efficacy properties.
Laboratory studies conducted on dogs treated with three tick control formulations showed different results. They demonstrated that the combination of the commercial formulation Vectra® 3D (DPP) containing the active ingredients dinotefuran (4.95 %), pyriproxifen (0.44 %), and permethrin (DPP) and the commercial formulation K9 Advantix® 55 (Bayer HealthCare, Shawnee mission, Kansas) containing imidacloprid (8.8 %) and permethrin (44.0 %; IP) provided a better monthly lasting protection against tick infestations than Frontline® Plus (Merial Ltd., Duluth, GA) containing fipronil (9.8 %) and (S)-methoprene (8.8 %; FM). Moreover, whereas both DPP and IP are permethrin-based actives, only DPP exhibited satisfactory protection against ticks at every time-point for one month. The DPP formulation, which produced a high (>96 %) residual efficacy, should be considered as a reliable veterinary prevention tool against infestations by the brown dog tick.
The efficacy of the tick control products depends on their mode of action, onset of activity and residual activity. Whereas permethrin was shown to be the fastest acaricide, fipronil was identified as the slowest one. Concentration of fipronil available on the skin and hairs of dogs was far below the required dose for efficacy on ticks within 24 hours of exposure 21 days after treatment. Fipronil and permethrin also exhibited considerable differences regarding repellency and knock-down effect. Fipronil exhibited a noticeable detachment effect on the ticks between 24 and 48 hours after infestation. Contrary to fipronil, permethrin is not only acaricidal but also exhibits repellency and knock-down effects. These properties are key factors for the prevention of tick attachment on the host and contributed clearly to the efficacy of the permethrin-based combination. Ticks, falling from the treated dogs within the first 10 min of exposure, are killed by permethrin in a few hours thus providing a high level of prevention against tick attachment for 1 month. The lower dose of permethrin applied to the K9 Advantix®-treated dogs and the differences in formulation between the two combinations may have contributed to reduce the efficacy of this combination.
There have been reports on a strain of brown dog ticks collected in Panama classified as highly resistant to permethrin, moderately resistant to amitraz, and susceptible to fipronil. Reports on other brown dog tick strains suggest that resistance to deltamethrin can occur, which indicates that resistance to pyrethroid acaricides may be a concern with this tick. However, studies suggest resistance varies among different tick populations. Vaccination of dogs and cats against fleas or ticks may be possible in the future, but is not a current option.2
- One-month comparative efficacy of three topical ectoparasiticides against adult brown dog ticks (Rhipicephalus sanguineus sensu lato) on mixed-bred dogs in controlled environment. Marie Varloudcorresponding author and Josephus J. Fourie
- Insecticide/acaricide resistance in fleas and ticks infesting dogs and cats. Tad B Colescorresponding author and Michael W Dryden