Poché et al. Parasites Vectors (2020) 13:391 https://doi.org/10.1186/s13071-020-04258-0 Parasites & Vectors RESEARCH Open Access Efcacy of a low dose fpronil bait against blacklegged tick (Ixodes scapularis) larvae feeding on white-footed mice (Peromyscus leucopus) under laboratory conditions David M. Poché*, Gregory Franckowiak, Tyler Clarke, Batchimeg Tseveenjav, Larisa Polyakova and Richard M. Poché Abstract Background: Lyme disease is the most prevalent vector-borne disease in the USA with cases continuing to increase. Current control measures have not been shown to be impactful, and therefore alternatives are needed. Treating pathogen reservoirs with low dose systemic acaricides in endemic areas may provide a useful tool for disrupting the cycle of the vector and pathogen. The purpose of this study was to determine the efcacy of a 0.005% fpronil bait, presented orally to white-footed mice, in controlling blacklegged tick larvae (larvae). Methods: Sixty mice were assigned to 3 treatment groups and three untreated control groups. All individually housed mice in treatment groups were exposed to 0.005% fpronil bait for 48 hours. Larvae were manually applied to mice within feeding capsules at one of three timepoints: Day 1, Day 9 and Day 15 post-exposure. For 4-days post- tick attachment, replete larvae were collected from water moats underneath each cage and attached larvae were observed by microscopy. Plasma from 4 treated mice at Day-1, Day 13 and Day 19, and 4 control mice (n 16) was collected to obtain fpronil plasma concentrations (CP). = Results: Fipronil bait did not appear to produce neophobia in mice, as the amount of bait eaten at 24- and 48-hours expo- sure did not difer signifcantly. The 48-hour fpronil bait exposure prevented 100% of larvae from feeding to repletion at Day 1, Day 9 and Day 15 post-treatment. Within the treatment groups, all larvae observable within the capsules expired and were prevented from detaching by Day 4. In contrast, within the control groups a total of 502 replete larvae were collected from moats and 348 larvae observable within the capsules successfully detached. CP averaged 948.9, 101.2 and 79.4 ng/ml for mice euthanized at Day 1, Day 9 and Day 15, respectively. No fpronil was detected in control mice. Conclusions: We provide early indication that low dose fpronil bait, orally presented to white-footed mice, can efectively control blacklegged tick larvae. Future research should modify the exposure duration and post-exposure tick attachment timepoints to simulate various feld scenarios under which successful efcacy might be obtained. Low dose fpronil bait could provide a cost-efective, practical means of controlling blacklegged ticks and other arthropod vectors. Keywords: Borrelia burgdorferi (sensu stricto), Blacklegged ticks, Ixodes scapularis, White-footed mice, Peromyscus leucopus, Fipronil bait, Acaricides, Systemic insecticides, Vector control *Correspondence: [email protected] Genesis Laboratories, Inc., Wellington, CO, USA © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Poché et al. Parasites Vectors (2020) 13:391 Page 2 of 15 Background the summer and take a blood meal from small rodents, Lyme disease is the most prevalent vector-borne dis- host-feeding heavily on white-footed mice. It is at this ease transmissible to man in the USA and cases have point that they acquire the B. burgdorferi (s.s.) spirochete. continued to increase from 2001 to present [1, 2], with Once larvae have blood-fed to repletion, they detach over 300,000 cases estimated to occur annually and a from the host and begin molting. Infected larvae will typ- geographical distribution that is continually expand- ically emerge to feed as nymphs the following spring. Te ing [2, 3]. In the USA, human instances of Lyme dis- risk of human exposure to Lyme disease is shown to be ease are most commonly reported in the midwestern/ a function of the local abundance of nymphal and adult north-central and northeastern regions [1, 4] where the ticks [17] and is strongly correlated with the density of blacklegged tick (Ixodes scapularis) serves as the pri- spirochete-infected ticks in the areas surrounding resi- mary pathogen vector for the Lyme disease spirochete dences [18]. Nymphs are believed to be the primary path- (Borrelia burgdorferi (sensu stricto)) with the white ogen reservoir responsible for B. burdorferi transmission footed mouse (Peromsyscus leucopus) serving as a pri- [2] and may be responsible for as much as 90% of Lyme mary reservoir host for immature blacklegged ticks in disease cases each year [19]. Risk of B. burgdorferi (s.s.) these regions [5]. infection is shown to increase in response to increases Initial Lyme disease symptoms are fu-like and accom- in infected nymphs [20]. Given the issues regarding tra- panied by a specifc rash present in 60–80% of patients ditional acaricide application and B. burgdorferi (s.s.) risk referred to as erythema migrans [6]. If cases are not factors such as density of nymphs and proximity of host quickly treated with antibiotics, infection can spread to animals, strategies such as targeting white-footed mice joints, the heart, and nervous system [4]. Lyme disease is with an acaricide, aimed at reducing larval tick density, difcult to diagnose, partly because of clinical non-spec- could prove benefcial. A targeted approach would mark- ifcity [7], and it is not uncommon for patients treated edly reduce the amount of active ingredient being applied with 2–4 weeks of antibiotics to sufer from post-treat- in the feld, which would pose a reduced risk to non-tar- ment Lyme disease syndrome (PTLDS) which can last for get organisms. Signifcantly reducing larvae feeding on more than six months and may last for many years [8]. white-footed mice could reduce the density of incoming Te economic burden of Lyme disease is substantial with nymphs and reduce B. burgdorferi (s.s.) infection rates. the cost to the American Healthcare System having been Fipronil is a phenylpyrozol that interferes with arthro- estimated to be between $712 million and $1.3 billion pod central nervous systems by blocking the GABA- per year, and annual fees per patient sufering from Post- gated and glutamate-gated chloride channels [21]. It Treatment Lyme Disease Syndrome (PTLDS) are esti- has shown promise in controlling several arthropod mated to be $3000 and $3800 [9]. Tus, the disease is still pests and has been explored for use in tick control. One of understandable importance in the USA and alternative such method being explored is the use of the Select TCS methods of disease prevention and vector control should bait box (EPA Est. No. 85306-CT-001). Tis approach continue to be investigated to alleviate the signifcant involves a bait station, which is flled with attractive burden placed upon medical practitioners and patients. bait and is ftted with a cotton or felt wick treated with Acaricide application methods aimed at control- a concentration of 0.70–0.75% fpronil that is topically ling blacklegged ticks are among the more promising applied to white-footed mice entering the bait station approaches for Lyme disease prevention. However, large- [22–24]. While the approach has reduced ticks under scale pesticide application has been hindered largely experimental conditions, its defciencies have hindered as a biproduct of environmental concerns [10, 11]. Tra- widespread use. Te bait station is noted as being costly ditional methods such as dusting or blanket spraying and needing to be periodically replaced [24]. Mice are require a large volume of acaricide and a high concen- also able to avoid the wick or will routinely remove tration of active ingredient in the formulations [11] that them for use as bedding material [23]. Tus, many mice are exponentially higher than what would be required to entering the bait stations to feed are not inoculated and control tick larvae and nymphs [12–14]. Te greatest risk use of a single wick with fpronil requires bait stations factors for Lyme disease are exposure to infected Ixodes be replaced. Additionally, the product is a restricted use spp. ticks and reservoir host animals, particularly the pesticide, meaning that only licensed pest control pro- white-footed mouse, in woody, grassy areas [15]. fessionals may use it, which further limits utilization. Te life-cycle of blacklegged ticks takes approximately Bait stations/boxes will need to be baited regardless of two years to complete and is composed of four life stages the route of acaricide administration (i.e. topical, oral). (eggs, larvae, nymphs and adults). After the eggs hatch, Tus, a practical and cost-efective solution would be to they require a blood meal at each subsequent life stage to load the bait stations with a low dose acaricide bait for survive and develop [16].