Efficacy of oral afoxolaner plus milbemycin oxime chewables against induced infestations with Dermacentor reticulatus in dogs.

Abstract

The efficacy of afoxolaner plus milbemycin oxime (AFX + MO) combination chewables (NexGard Spectra®, Merial) and AFX single-entity chewables (NexGard®, Merial) against induced infestations with Dermacentor reticulatus ticks was evaluated in dogs. Thirty dogs were assigned to blocks of three animals each based on pre-allocation tick counts and were randomly allocated to one of three groups: untreated (control), treated with a combination of AFX + MO chewables to be as close as possible to the minimum effective dose of AFX + MO (2.5 + 0.5mg per kg body weight), and treated with a combination of NexGard® chewables to be as close as possible to the minimum effective dose of AFX (2.5mg per kg body weight). Treatments were administered orally once on day 0. Starting 2days before treatment administration, each dog was infested with approximately 50 ticks weekly for six consecutive weeks. Live ticks were counted at ∼48h post-treatment (removal count) and at ∼48h (in situ counts) and ∼72h (removal counts) following each post-treatment infestation. Treatment with both AFX + MO and NexGard® chewables rapidly eliminated the existing tick infestations (100% efficacy) within 2days following treatment administration. Weekly re-infestations were controlled for a minimum of 5weeks with the efficacy ranging from 92.2 to 99.7% based on ∼48h post-treatment in situ counts and between 99.0 and 100% based on ∼72h post-treatment removal counts (p < 0.0001 at each occasion). This study demonstrated a high efficacy of both AFX + MO chewable and NexGard® chewable treatments against infestations of dogs with D. reticulatus ticks for at least 5weeks. In addition, this study indicated no interference between the two compounds with respect to the acaricidal activity provided by AFX.