Evaluation of fluralaner as an oral acaricide to reduce tick infestation in a wild rodent reservoir of Lyme disease

Abstract

Background: Lyme disease (LD) is an increasing public health threat in temperate zones of the northern hemisphere, yet relatively few methods exist for reducing LD risk in endemic areas. Disrupting the LD transmission cycle in nature is a promising avenue for risk reduction. This experimental study evaluated the efficacy of fluralaner, a recent oral acaricide with a long duration of effect in dogs, for killing Ixodes scapularis ticks in Peromyscus maniculatus mice, a known wildlife reservoir for Borrelia burgdorferi in nature. Methods: We assigned 87 mice to 3 fluralaner treatment groups (50 mg/kg, 12.5 mg/kg and untreated control) administered as a single oral treatment. Mice were then infested with 20 Ixodes scapularis larvae at 2, 28 and 45 days post-treatment and we measured efficacy as the proportion of infesting larvae that died within 48 h. At each infestation, blood from 3 mice in each treatment group was tested to obtain fluralaner plasma concentrations (C p). Results: Treatment with 50 mg/kg and 12.5 mg/kg fluralaner killed 97% and 94% of infesting larvae 2 days post-treatment, but no significant effect of treatment on feeding larvae was observed 28 and 45 days post-treatment. Mouse C p did not differ significantly between the two tested doses. Mean C p decreased from 13,000 ng/ml in the 50 mg/kg group and 4000 ng/ml in the 12.5 mg/kg group at Day 2 to < 100 ng/ml in both groups at Day 45. Conclusions: We provide the first evidence that fluralaner is effective for killing immature ticks in Peromyscus mice, a first step in evaluating its potential for treating wild rodents as a public health intervention to reduce LD risk in endemic areas.

Efficacy of a low dose fipronil bait against blacklegged tick (Ixodes scapularis) larvae feeding on white-footed mice (Peromyscus leucopus) under laboratory conditions

“…As was the case during the fluralaner studies conducted by Pelletier et al [26], in the present study the CP of fipronil for mice was highly variable, particularly at Day 1 post-exposure. The mean CP of fipronil was markedly lower at Day 1 post-exposure (948.9 ng/ml) when compared with the mean CP of fluralaner at Day 2 post exposure (0.005%= 13,815 ng/ml; 0.0.00125%= 4594 ng/ ml); however, we should note that consumption by the Day-1 mice was low relative to the TDay9-and TDay15 mice.…”

“…It was assumed that some larvae attached to feces or other debris in moats and were not found during scans. The difficulties associated with tick feeding have been described in previous studies [26,30,51]. Larvae are particularly challenging to recover because of their small size (≤ 0.8 mm in length).…”

“…During previous laboratory research, fipronil baits, at concentrations of 0.097% and 0.0485%, presented orally to house mice (Mus musculus) were 100% efficacious in preventing larval blacklegged ticks from feeding to repletion when larvae were fed on mice immediately following a 48-hour exposure period [25]. A more recent laboratory study evaluated the use of 0.005% and 0.0015% fluralaner baits presented orally to deer mice (Peromyscus maniculatus) [26]. When mice were exposed to these baits for 24 hours, at Day-2 post-exposure, blacklegged tick larvae were reduced by up to 97% and 94%, respectively.…”

“…The study conducted by Pelletier et al [26] estimated efficacy two days after tick attachment, only. Larvae feed for ~4 days after which replete larvae will drop off and begin molting [36].…”

“…The results of these above studies are useful; however, additional research is warranted. The above studies utilized house mice [ 25 ] and deer mice [ 26 ], respectively. While these studies provide insights regarding the potential for blacklegged tick control, additional mammalian species should be investigated, particularly the white-footed mouse.…”