Efficacy of an oral combination of afoxolaner and milbemycin oxime for the prevention of transmission of Babesia canis by Dermacentor reticulatus ticks to dogs

Background: Canine babesiosis is a tick-borne disease of significant veterinary importance in dogs. It is caused by Babesia canis in Europe, where it is transmitted by Dermacentor reticulatus ticks. Methods : A blinded, randomized, Good Clinical Practice (GCP) and negative control experimental study was conducted to verify the efficacy of NexGard Spectra ^® in reducing the transmission of B. canis by D. reticulatus to dogs. NexGard Spectra ^® (IVP) is an oral product for dogs combining afoxolaner an acaricide/insecticide compound from the isoxazoline class and milbemycin oxime a nematicide compound from the macrocyclic lactone class. Three groups of eight dogs were used, one group orally treated on Day 0 with the IVP at the minimum recommended dose and two untreated control groups. On Day 1, dogs from the treated group and from the control group 1 were infested with 50 D. reticulatus adult ticks of 50/50 sex ratio infected with B. canis at a 23% infection rate. On Day 28, dogs from the treated group and from the control group 2 were infested similarly to those on Day 1. Ticks were removed 6 days after each infestation. Results: Seven to nine days after each infestation, all untreated control dogs displayed clinical signs of canine babesiosis, i.e. lethargy, and/or dark urine, and/or >39.5°C rectal temperature. Blood was collected for microscopical blood smear examination, and for PCR analysis. The blood smears from all untreated control dogs were positive for Babesia and all the PCR analyses were positive for B. canis. The control dogs were rescue treated. All control dogs were confirmed positive for B. canis by IFA on Day 21 (control group 1) and on Day 42 (control group 2). None of the IVP-treated dogs expressed any clinical sign of canine babesiosis following each of the two infestations of Days 1 and 28 and until Day 56. Blood was collected for IFA and PCR analyses from the treated dogs on Days 21, 28, 42 and 56, and all results were negative. Conclusion: In this study, the antiparasitic treatment prevented the transmission of B. canis to dogs following induced infestations.