Fluralaner Baits Reduce the Infestation of Peromyscus spp. Mice (Rodentia: Cricetidae) by Ixodes scapularis (Acari: Ixodidae) Larvae and Nymphs in a Natural Environment

A scoping review of applied tick control research in North America: funding, implementation, and advancement

Geographic ranges of ticks and tick-borne pathogens within North America are shifting due to environmental changes and human-driven activities, with species of public health concern presenting a multifaceted risk to human health. Innovative strategies and continued collaboration to control tick populations are needed to combat this growing threat. We conducted a scoping review of the literature to describe the nature of applied tick control research conducted in North America (Canada, Mexico, and the United States) to date, with the goal of describing key concepts and identifying gaps in this research area. A total of 244 articles met our inclusion criteria and were reviewed for patterns in applied tick control authorship and funding, study location, target species, and control methodology. Most studies (83.6%) were conducted exclusively in the United States and 75% focused on ticks of public health concern, principally Amblyomma americanum (Linnaeus, Acari: Ixodidae), Dermacentor variabilis (Say, Acari: Ixodidae), Ixodes scapularis Say (Acari: Ixodidae), and Rhipicephalus sanguineus (Latreille, Acari: Ixodidae). The majority of funding was provided through US federal agencies, predominantly the Centers for Disease Control and Prevention and the United States Department of Agriculture. Ixodes scapularis was the target of over 50% of identified articles, with the majority of research conducted within 3 states in the Northeast region of the U.S. Only 8.2% of included studies evaluated integrated tick management interventions. We note gaps in tick control research regarding (i) non-Ixodes medically relevant tick species, (ii) endemic range coverage, and (iii) control methodologies evaluated.

A systematic review of fluralaner as a treatment for ectoparasitic infections in mammalian species

Fluralaner (Bravecto™) is a novel isoxazoline ectoparasiticide used for controlling ectoparasites of domestic mammals and is increasingly being used on wildlife. The aim of this systematic review was to evaluate the efficacy, pharmacokinetics, and safety of fluralaner on mammals given its increasing use. The search was performed in GoogleScholar and the SciFinder databases using the terms 'fluralaner' and 'Bravecto™', and was concluded on 30th August, 2024. A total of 250 references were initially saved and reduced to 121 peer-reviewed journal articles using PRISMA guidelines, based on the removal of duplicates, those published in low quality journals (ranked less than Q2), and limiting publications to clinical trials. Articles were then categorised and ranked using the level of evidence, Cochrane 'risk of bias' assessment tool, methodological quality, and study size. Overall, the efficacy of fluralaner has been assessed on 14 mammalian species, and pharmacokinetic investigations conducted on 15. Fluralaner was mostly effective at treating some ectoparasites on captive individuals when there was little chance of re-infection; however, it did not prevent bites from blood-sucking ectoparasites and could not prevent blood-borne pathogen transfer to host animals. Very few studies have investigated the pharmacokinetics of fluralaner, and hence were difficult to compare; however, wombats differed greatly from their eutherian counterparts in their Cmax and t½ values and require further investigation. Overall, fluralaner was deemed moderately safe; however, most studies were classified as fair in terms of quality and most studies were based on small or very small sample numbers. Nineteen studies reported side effects, one of which included signs of severe neurological toxicity, with most of the articles not reporting on safety either positively or negatively. Concerns were raised regarding the extended time fluralaner was detected in faeces and subsequently environmental contamination is a concern. No longer-term impacts of the use of fluralaner have been investigated, and wider implications of the use of this ectoparasiticide have not yet been assessed.

Rodent-targeted fluralaner baiting reduces the density of Borrelia burgdorferi-infected questing Ixodes scapularis ticks in a peri-urban setting in southern Canada

Lyme disease (LD) is a threat to public health in southern regions of Canada. In response, we used a One Health approach to design an integrated intervention in a high-incidence LD community in southern Québec aiming to increase preventive behaviours in the population and reduce the density of Borrelia burgdorferi-infected Ixodes scapularis ticks in the environment. The environmental component involved distributing fluralaner baits to rodents around residential properties and public trails from 2019 to 2023. Effectiveness was measured by changes in the density of questing nymphs (DON) and the prevalence of B. burgdorferi-infected nymphs (NIP). Treated areas were compared to areas located between 0 and 250 m from treatment locations and to untreated areas located >250 m away. The DON was reduced by 39 % (95 % confidence interval [95 % CI] = 1 - 62 %) in treated areas when compared to untreated areas in 2021 and 2022. Over this same period, in areas between 0 and 250 m, the DON was lower when closer to bait stations (P = 0.001). The treatment significantly reduced the NIP in treated area in 2020 (Odds ratio [OR] = 0.87 [95 % CI 0.08 - 0.98]), 2021 (OR = 0.85 [95 % CI 0.26 - 0.97], and 2022 (OR = 0.88 [95 % CI 0.12 - 0.98]), and in areas between 0 and 250 m in 2020 (OR = 0.87 [0.08 - 0.98]) and 2021 (OR = 0.84 [95 % CI 0.25 - 0.97]). This study confirms the potential of rodent-targeted fluralaner baiting for reducing the density of infected questing nymphs in peri‑urban environments.

The effect of fluralaner treatment of small mammals on the endemic cycle of Borrelia burgdorferi in a natural environment

Among approaches aimed at reducing Lyme disease risk in the environment, those targeting reservoirs of Borrelia burgdorferi Johnson are promising because they have the potential to reduce both the density of questing Ixodes scapularis Say (Acari: Ixodidea) ticks and the prevalence of B. burgdorferi in the tick population. In this 4-yr field study, we treated a population of wild small mammals with 2 densities of fluralaner baits and investigated the effect of the treatment on 3 parameters of the endemic cycle of B. burgdorferi: (i) the prevalence of infected Peromyscus mice (PIM), (ii) the density of questing nymphs (DON), and (iii) the prevalence of infected questing nymphs (NIP). We demonstrated that fluralaner baiting is effective at reducing tick infestation of Peromyscus mice, the main reservoir of B. burgdorferi in central and northeastern North America, in the laboratory and the field. Results from this study showed a significant decrease in B. burgdorferi infection in mice (odds ratio: 0.37 [CI95: 0.17 to 0.83]). A reduction in the DON between 45.4% [CI95: 22.4 to 61.6] and 62.7% [CI95: 45.9 to 74.2] occurred in treated area when compared with control areas. No significant effect was reported on the NIP. These results confirm the hypothesis that fluralaner baits have an effect on B. burgdorferi endemic cycle, with the potential to reduce the density of B. burgdorferi-infected ticks in the environment. Further studies performed in various habitats and public health intervention contexts are needed to refine and operationalize this approach for reducing Lyme disease risk in the environment.

A rodent and tick bait for controlling white-footed mice (Peromyscus leucopus) and blacklegged ticks (Ixodes scapularis), the respective pathogen host and vector of the Lyme disease spirochetes

A promising alternative approach to conventional vector and rodent control practices is the use of a bait containing a rodenticide and acaricide in controlling vectors and pathogen reservoirs concurrently. In the United States, Lyme disease continues to be the most prevalent vector-borne disease with approximately 500,000 Lyme disease cases estimated each year. Previous research has demonstrated the usefulness of a low dose fipronil bait in controlling Ixodes scapularis larvae feeding on white-footed mice. However, considering white-footed mice can be an unwanted species because of their association with tick-borne disease and hantaviruses, a combination rodent and tick bait (RTB) might provide a useful alternative to encourage additional community participation in integrated tick management (ITM) efforts. The purpose of this research was to evaluate the use of RTB (0.025 % warfarin, 0.005 % fipronil) in controlling white-footed mice and I. scapularis larvae. Studies were designed in part based on Environmental Protection Agency (EPA) guidelines. A laboratory choice test was conducted to evaluate the use of RTB in controlling white-footed mice over 15-day exposure when they were exposed to an alternative diet. Mice were observed every day for mortality and signs of warfarin toxicity. A simulated field test was conducted to evaluate the use of RTB, presented in the presence of an alternative diet, in controlling I. scapularis parasitizing white-footed mice over 4-day exposure. Mice were fitted with capsules and manually infested with I. scapularis larvae. The inside of each capsule was observed to evaluate tick attachment. Replete larvae detaching from each mouse were collected. Blood was collected from all treatment group mice via cardiac puncture to determine the fipronil sulfone concentration in plasma for each animal. Results indicated that RTB would be adequately consumed in the presence of an alternative diet under laboratory and simulated field conditions. Treatment with RTB resulted in 100 % mortality of white-footed mice during 15-day exposure and prevented 100 % larvae from feeding to repletion during 4-day exposure. All mice succumbing to RTB showed signs of warfarin toxicity. All mice parasitized with ticks that were exposed to RTB had fipronil sulfone detectable in plasma, with even the lowest concentration detected (8.1 parts per billion) controlling 100 % parasitizing I. scapularis larvae. The results suggest that RTB could be a useful means of rodent and tick control for use in ITM programs.

Pharmacological studies and pharmacokinetic modelling to support the development of interventions targeting ecological reservoirs of Lyme disease

The development of interventions targeting reservoirs of Borrelia burgdorferi sensu stricto with acaricide to reduce the density of infected ticks faces numerous challenges imposed by ecological and operational limits. In this study, the pharmacokinetics, efficacy and toxicology of fluralaner were investigated in Mus musculus and Peromyscus leucopus mice, the main reservoir of B. burgdorferi in North America. Fluralaner showed rapid distribution and elimination, leading to fast plasma concentration (Cp) depletion in the first hours after administration followed by a slow elimination rate for several weeks, resulting in a long terminal half-life. Efficacy fell below 100% while Cp (± standard deviation) decreased from 196 ± 54 to 119 ± 62 ng/mL. These experimental results were then used in simulations of fluralaner treatment for a duration equivalent to the active period of Ixodes scapularis larvae and nymphs. Simulations showed that doses as low as 10 mg/kg have the potential to protect P. leucopus against infestation for a full I. scapularis active season if administered at least once every 7 days. This study shows that investigating the pharmacology of candidate acaricides in combination with pharmacokinetic simulations can provide important information to support the development of effective interventions targeting ecological reservoirs of Lyme disease. It therefore represents a critical step that may help surpass limits inherent to the development of these interventions.

Efficacy of a federally approved flea bait, orally administered to white-footed mice (Peromyscus leucopus), against blood feeding Ixodes scapularis larvae under simulated field conditions

A promising alternative approach to conventional vector control practices is the use of systemic insecticides/acaricides orally administered to relevant mammalian host species to control blood feeding disease vectors. In the United States, Lyme disease continues to be the most prevalent vector-borne disease with the Centers for Disease Control and Prevention estimating approximately 500,000 Lyme disease infections each year. Previous research has demonstrated the potential usefulness of a low dose fipronil bait in controlling Ixodes scapularis larvae feeding on white-footed mice. However, no such acaricide-only product is approved for use in treating white-footed mice to control I. scapularis. The purpose of the study was to evaluate the use of a federally approved fipronil flea control bait (Grain Bait) in controlling I. scapularis parasitizing white-footed mice (Peromyscus leucopus). A simulated field trial was conducted in which Grain Bait was presented to grouped white-footed mice alongside an alternative diet for 168 h. Mice were fitted with capsules and manually parasitized with I. scapularis larvae. Replete larvae detaching from each mouse were collected and monitored for molting to nymphs. The inside of each capsule was observed to evaluate tick attachment. Blood was collected from all Treatment group mice via cardiac puncture to determine the fipronil sulfone concentration in plasma (CP) for each animal. Results indicated that Grain Bait would be consumed in the presence of an alternative diet and that bait acceptance was greater for males, relative to females. Treatment with Grain Bait prevented 100% larvae from feeding to repletion at Day 7 post-exposure and prevented 80% of larvae from feeding to repletion and 84% from molting at Day 21 post-exposure, relative to Control groups. Molted nymphs were not recovered from mice that had CP detectable ≥18.4 ng/ml. The results suggest that this federally approved flea product could be utilized for tick control and that other medically important vector-host relationships should be considered.

Does Experimental Reduction of Blacklegged Tick (Ixodes scapularis) Abundance Reduce Lyme Disease Incidence?

Controlling the abundance of blacklegged ticks is considered the foundation for the prevention of human exposure to pathogens transmitted by these vectors in eastern North America. The use of broadcast or host-targeted acaricides is generally found to be effective at reducing the local abundance of ticks. However, studies that incorporate randomization, placebo controls, and masking, i.e., "blinding", generally find lower efficacy. The few studies that include measurements of human-tick encounters and cases of tickborne disease have not shown impacts of acaricidal treatments. We compile literature on relevant studies from northeastern North America to address possible causes for discrepancies in study outcomes and suggest possible mechanisms that could underlie the diminished efficacy of tick control in reducing cases of tickborne disease in people.

Orally delivered fipronil-laced bait reduces juvenile blacklegged tick (Ixodes scapularis) burdens on wild white-footed mice (Peromyscus leucopus)

While the topical acaricidal treatment of rodent pathogen reservoirs has been readily explored over the past several decades, oral systemic acaricidal treatment is only recently gaining traction as an alternative approach to the management of ticks and tick-borne pathogens. Recent laboratory tests have shown promise in the effectiveness of this systemic strategy against the blacklegged tick (Ixodes scapularis) and a Canadian field evaluation was recently published, but no recent field data from the United States yet exist. With this research, we sought to field deploy a commercially available fipronil-laced bait (Kaput® Flea Control Bait, Scimetrics LLC., Wellington, CO, USA; 0.005% fipronil; Environmental Protection Agency Reg. No. 72500-28), in an alternate use targeting white-footed mice (Peromyscus leucopus) to determine bait acceptance and potential impacts to juvenile I. scapularis burdens. Bait was readily accepted by wild P. leucopus and other rodent reservoirs. An ad libitum distribution strategy as well as placing smaller volumes of fipronil-laced bait within individual Sherman traps both resulted in significant reductions (57-94%) in juvenile I. scapularis burdens as compared to control over two years. The oral delivery of systemic acaricides shows promise in reduction of I. scapularis burdens on P. leucopus and should be further explored to determine effectiveness on host-seeking tick abundances, associated pathogen infection, and potentially incorporated into integrated tick management programs.

Rodent-targeted approaches to reduce acarological risk of human exposure to pathogen-infected Ixodes ticks

In the United States, rodents serve as important hosts of medically important Ixodes ticks, including Ixodes scapularis and Ixodes pacificus, as well as reservoirs for human pathogens, including Anaplasma phagocytophilum, Borrelia burgdorferi sensu stricto (s.s.), and Babesia microti. Over the last four decades, different methods to disrupt enzootic transmission of these pathogens between tick vectors and rodent reservoirs have been developed and evaluated. Early work focused on self-application of topical acaricide by rodents to kill infesting ticks; this resulted in two different types of commercial products based on (i) delivery of permethrin to rodents via impregnated cotton offered as nesting material or (ii) application of fipronil to rodents via an impregnated wick as they navigate through a bait box to reach a food source. More recent work has focused on approaches where acaricides, antibiotics, or a vaccine against Bo. burgdorferi s.s. are delivered orally via rodent food baits. Of these, the oral vaccine and oral acaricide are nearest to commercialization. Other approaches in early stages of development include anti-tick vaccines for rodents and use of heritable genome editing to engineer white-footed mice (Peromyscus leucopus) that are refractory to Bo. burgdorferi s.s. In this review, I first outline general benefits and drawbacks of rodent-targeted tick and pathogen control methods, and then describe the empirical evidence for different approaches to impact enzootic pathogen transmission and acarological risk of human exposure to pathogen-infected Ixodes ticks. Rodent-targeted methods remain promising components of integrated tick management approaches but there are concerns about the robustness of the impact of existing rodent-targeted products across habitats and variable tick host communities, and in some cases also for the implementation cost in relation to what homeowners in Lyme disease endemic areas say they are willing to pay for tick control.