BACKGROUND : The ability of the topical spot-on Advantix® (50 % permethrin/10 % imidacloprid) to prevent
transmission of Ehrlichia canis by infected Rhipicephalus sanguineus ticks to dogs has previously been reported. The
recent market introduction of chewable tablets containing the novel compounds, afoxolaner (NexGard™) and
fluralaner (Bravecto™) enabled us to conduct a comparative efficacy study with respect to the ability of these three
products to block transmission of E. canis by ticks to dogs. The speed of kill, immediate drop-off rate and
anti-attachment efficacy of the respective products were also studied.
METHODS : The study was a blinded parallel group design, wherein 32 dogs were randomised into four different
groups of eight dogs. Group 1 served as negative placebo control, group 2 and 3 were treated on Days 0, 28 and
56 with NexGard™ and Advantix®, respectively. Group 4 was dosed once on Day 0 with Bravecto™. For tick efficacy
assessments 50 non-infected ticks were placed onto the dogs on Days 30, 35, 42, 49, 56, 63, 70, 77 and 84 and on
animal tick counts were performed at 3 h, 6 h and 12 h after infestation. To evaluate the ability to block transmission of
E. canis, each dog was challenged by releasing 80 adult E. canis-infected R. sanguineus ticks into their sleeping kennels
on Days 31, 38, 45 and 52. The animals were monitored for clinical signs of monocytic ehrlichiosis (pyrexia and
thrombocytopenia) and were tested for E. canis DNA by PCR and for specific antibodies using IFA. A dog was
considered infected with E. canis if both PCR and IFA yielded positive test results up to Day 84.
RESULTS : Mean arithmetic tick counts on dogs treated with the Advantix® spot-on were significantly (P < 0.0005) lower
throughout the study as compared with the negative controls and was, with respect to the speed of kill and resulting
onset of acaricidal efficacy, superior over NexGard™ and Bravecto™ at all time points in the 12 h period observed (3 h,
6 h and 12 h). None of the dogs treated with the Advantix® spot-on became infected with E. canis, whereas six out of
eight untreated control dogs acquired the infection. Furthermore, E. canis infection was diagnosed in four out of eight
dogs treated with NexGard™ and in two out of eight dogs treated with Bravecto™.
CONCLUSIONS : The speed of kill of the two recently registered systemic compounds against R. sanguineus was not
sufficiently fast to prevent transmission of E. canis and resulted in only low partial blocking and protection capacity
while Advantix® effectively blocked transmission of E. canis to dogs in the challenge period and thus provided
adequate protection for dogs against monocytic ehrlichiosis.