Early onset of pre-lethal effects of lotilaner (Credelio) on Amblyomma americanum ticks on experimentally infested dogs.

Abstract

BACKGROUND: The speed with which acaricides paralyze and kill ticks is relevant to impeding pathogen transmission. The objective of this study was to assess early-onset lotilaner effects on the motility and weights of Amblyomma americanum ticks collected from treated dogs. METHODS: Twelve healthy dogs were randomized between two groups to receive either lotilaner (Credelio) on Day 0 or to be sham treated. On Day 7, 25 male and 25 female A. americanum were placed under bandages, two on each flank of each dog. After 30 or 45&#xa0;min, all unattached ticks were removed and T&#x2009;=&#x2009;0 was set. At T&#x2009;=&#x2009;2, 4, 8 and 24&#xa0;h post attachment, 5 attached ticks removed from each bandage on each dog were weighed, assessed by blinded observers for righting ability and movement recorded. RESULTS: After the infestation period significantly fewer treated than control dogs had 20 ticks attached (50.0% versus 91.7%, P&#x2009;=&#x2009;0.0015). At 24&#xa0;h post attachment, mean weights of ticks from treated dogs (males 1.69&#xa0;mg; females 2.72) were significantly less than ticks from controls (males 2.66&#xa0;mg; females 4.67) (P&#x2009;=&#x2009;0.0002; P&#x2009;<&#x2009;0.0001). Mean tick weights from the treated group were significantly lower at 24&#xa0;h than at earlier time points (P&#x2009;<&#x2009;0.0307; P&#x2009;=&#x2009;0.0021). At 4 and 8&#xa0;h, significantly fewer ticks from treated (14.3%, 0.0%, respectively) than from control dogs could right (73.3%, 70.0%) (P&#x2009;<&#x2009;0.0001; P&#x2009;=&#x2009;0.0024) (at 24&#xa0;h, all ticks from treated dogs were dead), and distance moved was significantly less at all time points (P&#x2009;=&#x2009;0.0413; P, P&#x2009;<&#x2009;0.0001). Mean and maximum velocity of ticks from treated dogs were significantly lower, relative to controls, at 4 and 8&#xa0;h (P&#x2009;&#x2264;&#x2009;0.0001). Within the treated group, collected ticks had significantly lower mean and maximum velocities at 4 and 8&#xa0;h compared to 2&#xa0;h (P&#x2009;<&#x2009;0.0042; P&#x2009;<&#x2009;0.0194). CONCLUSION: The observed changes indicate that lotilaner may disrupt tick attachment. In ticks that attached, a progressive impairment of neuromuscular processes began within 2&#xa0;h. Those irreversible changes could substantially reduce the risk of pathogen transmission from tick to host.