Efficacy of Afoxolaner Alone or in Combination with Milbemycin Oxime against Rhipicephalus sanguineus Lato Sensu in Naturally Infested Dogs in Colombia

Abstract

The brown dog tick (Rhipicephalus sanguineus lato sensu) is the tick that most affects dogs worldwide and is therefore the main blood pathogen vector in dogs. The efficacy of afoxolaner 2.7 to 7.1 mg/kg NexGard ® (group A) and afoxolaner plus milbemycin oxime 2.5 to 5.4 mg/kg and 0.5 to 1.1 mg/kg respectively NexGard Spectra ® (Group B) against R. sanguineus, was evaluated in naturally in-fected sheltered dogs under high challenging conditions in four different areas of Colombia (Antioquia, Córdoba, Santander, and Meta). Tick counts (alive, dead, attached, and unattached) were performed on treated dogs, the average was calculated for the different areas to evaluate the efficacy of each treatment at six different times post-treatment (24 h, 48 h, 7 d, 14 d, 21 d, 30 d). None of the dogs showed adverse events related to the treatments. The average tick number pre-treatment was 68 in group A and 78.3 for group B indicating a strong natural infection of the dogs and their environment. Efficacy after 24 h against R. sanguineus was always above 90% with ≥97.4% for NexGard ® and ≥93.7% for NexGard Spectra ® . Consistent results were observed along all the observation periods with final efficacies (day 30) of ≥99.8% and 98.3% for NexGard ® and NexGard Spectra ® , respectively. In conclusion, both NexGard ® and Nexgard Spectra ® provided a curative effect and sustained efficacy against Rhipicephalus sanguineus for at least 30 days in highly contaminated shelter environments.