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. 2021 Jun 13;14(1):322.
doi: 10.1186/s13071-021-04817-z.

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

Martha J Wenger  1 , Todd M Kollasch  2 , Madeline C Burke  1 , Livvy Jones  3 , Casey Locklear  2 , Makaela Hedberg  1 , Lauren Miller  1 , Sydnie Reeves  1 , Debra Ritchie  1 , Anthony J Rumschlag  2 , William G Ryan  4 , Vicki Smith  1 , Cameron Sutherland  1 , Kathryn E Reif  1 , Brian H Herrin  1
Affiliations

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

Martha J Wenger et al. Parasit Vectors. .

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 min, all unattached ticks were removed and T = 0 was set. At T = 2, 4, 8 and 24 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 = 0.0015). At 24 h post attachment, mean weights of ticks from treated dogs (males 1.69 mg; females 2.72) were significantly less than ticks from controls (males 2.66 mg; females 4.67) (Pmale = 0.0002; Pfemale < 0.0001). Mean tick weights from the treated group were significantly lower at 24 h than at earlier time points (Pmale < 0.0307; Pfemale = 0.0021). At 4 and 8 h, significantly fewer ticks from treated (14.3%, 0.0%, respectively) than from control dogs could right (73.3%, 70.0%) (P4h < 0.0001; P8h = 0.0024) (at 24 h, all ticks from treated dogs were dead), and distance moved was significantly less at all time points (P2h = 0.0413; P4h, P8h < 0.0001). Mean and maximum velocity of ticks from treated dogs were significantly lower, relative to controls, at 4 and 8 h (P ≤ 0.0001). Within the treated group, collected ticks had significantly lower mean and maximum velocities at 4 and 8 h compared to 2 h (Pmean < 0.0042; Pmax < 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 h. Those irreversible changes could substantially reduce the risk of pathogen transmission from tick to host.

Keywords: Acaricide; Amblyomma americanum; Canine; Credelio; EthoVision XT; Isoxazoline; Lone star tick; Lotilaner; Motility.

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Conflict of interest statement

MJW, MCB, LJ, MH, LM, SR, DR, CS and KER have no competing interests. TMK, CL, AJR are employees of Elanco Animal Health. WGR has received payments for clinical research and consulting fees from Elanco Animal Health. BHH has received honoraria, expense reimbursement and research support from Elanco Animal Health.

Figures

Fig. 1
Fig. 1
At 2 h post attachment following 24 h incubation: live Amblyomma americanum removed from sham-treated control dogs (top); dead A. americanum removed from lotilaner-treated dogs (bottom). Note between-group differences in legs and mouthparts
Fig. 2
Fig. 2
Number of Amblyomma americanum ticks taken from lotilaner-treated and sham-treated control dogs that were able to right within 30 s of being placed upside down (no ticks taken from treated dogs were able to right at 8- and 24-h time points post attachment, i.e. value = 0)
Fig. 3
Fig. 3
Example of heat maps created using the video software. Left: heat map of Amblyomma americanum tick from lotilaner-treated dog; Right: heat map of tick from sham-treated control dog. Darker blue represents less time spent in the arena, darker red more time
See this image and copyright information in PMC

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