Density of Ixodes scapularis ticks on Monhegan Island after complete deer removal: a question of avian importation?

Summer collection of multiple southern species of ticks in a remote northern island in Japan and literature review of the distribution and avian hosts of ticks

Expansion of ticks and tick-borne diseases is of increasing concern worldwide. To decrease the risk of ticks and tick-borne diseases to public health, understanding the mechanisms of their current distribution and future expansion is needed. Although tick distribution has been studied globally on continents and large islands that are inhabited by large mammals, less attention has been paid to remote islands. However, small islands are often important stopover sites for migratory birds that may contribute to long-distance dispersal of ticks. Therefore, islands would be a suitable system to rule out potential effects of mammals and to evaluate the contribution of birds to the expansion of ticks and tick-borne diseases. We collected questing ticks by dragging cloths over vegetation on Tobishima Island, northern Japan, in summer 2021, and conducted a literature search of the distribution and avian hosts of hard tick. We found several southern species of ticks (Haemaphysalis hystricis, H. formosensis, H. cornigera, Amblyomma testudinarium, and Dermacentor bellulus) on the island. These species have rarely or never been reported from the mainland of Japan at similar latitudes or higher, where large mammals are found. They are known vectors of tick-borne diseases, such as severe fever with thrombocytopenia syndrome. The present study suggests that migratory birds may contribute to the expansion of ticks and tick-borne diseases, and a remote island may function as a front line and/or a hub for their expansion. Evaluating tick fauna on remote islands used by migratory birds might be useful to monitor the expansion.

Inter-annual variation in prevalence of Borrelia burgdorferi sensu stricto and Anaplasma phagocytophilum in host-seeking Ixodes scapularis (Acari: Ixodidae) at long-term surveillance sites in the upper midwestern United States: Implications for public health practice

The geographic range of the blacklegged tick, Ixodes scapularis, and its associated human pathogens have expanded substantially over the past 20 years putting an increasing number of persons at risk for tick-borne diseases, particularly in the upper midwestern and northeastern United States. Prevention and diagnosis of tick-borne diseases rely on an accurate understanding by the public and health care providers of when and where persons may be exposed to infected ticks. While tracking changes in the distribution of ticks and tick-borne pathogens provides fundamental information on risk for tick-borne diseases, metrics that incorporate prevalence of infection in ticks better characterize acarological risk. However, assessments of infection prevalence are more labor intensive and costly than simple measurements of tick or pathogen presence. Our objective was to examine whether data derived from repeated sampling at longitudinal sites substantially influences public health recommendations for Lyme disease and anaplasmosis prevention, or if more constrained sampling is sufficient. Here, we summarize inter-annual variability in prevalence of the agents of Lyme disease (Borrelia burgdorferi s.s.) and anaplasmosis (Anaplasma phagocytophilum) in host-seeking I. scapularis nymphs and adults at 28 longitudinal sampling sites in the Upper Midwestern US (Michigan, Minnesota, and Wisconsin). Infection prevalence was highly variable among sites and among years within sites. We conclude that monitoring infection prevalence in ticks aids in describing coarse acarological risk trends, but setting a fixed prevalence threshold for prevention or diagnostic decisions is not feasible given the observed variability and lack of temporal trends. Reducing repeated sampling of the same sites had minimal impact on regional (Upper Midwest) estimates of average infection prevalence; this information should be useful in allocating scarce public health resources for tick and tick-borne pathogen surveillance, prevention, and control activities.

Barriers to Effective Tick Management and Tick-Bite Prevention in the United States (Acari: Ixodidae)

Lyme and other tick-borne diseases are increasing in the United States. Development of tick control tools have focused primarily on the blacklegged tick, Ixodes scapularis Say. Application of acaricides or entomopathogenic fungal agents to kill host-seeking ticks or ticks on rodents can suppress I. scapularis abundance in residential landscapes, but evidence is lacking for impact on human tick bites or tick-borne disease. Similar studies remain limited for the lone star tick, Amblyomma americanum (L.). Other knowledge gaps include how well homeowners and pest control companies perform in the broadcast application of tick-killing products, relative to high efficacy reported in research studies, and the tick-killing potential of natural product formulations exempt from Environmental Protection Agency registration. Area-wide control based on preventing ticks from feeding on their main reproductive host, the white-tailed deer, can suppress populations of both I. scapularis and A. americanum. Some studies also suggest an impact on Lyme disease cases, but this needs to be further validated in larger-scale intervention studies. The effectiveness, scale, cost, and implementation of various tick management strategies are important considerations in efforts to reduce human tick encounters and tick-borne disease. Additional barriers include weak incentives for industry and academia to develop, test, and register new tick and pathogen control technologies, including vaccines targeting humans, tick reproductive hosts, or wildlife pathogen reservoirs. Solutions will need to be 'two-pronged': improving the tick and pathogen control toolbox and strengthening the public health workforce engaging in tick control at local and state levels.

Impact of Land Use Changes and Habitat Fragmentation on the Eco-epidemiology of Tick-Borne Diseases

The incidence of tick-borne diseases has increased in recent decades and accounts for the majority of vector-borne disease cases in temperate areas of Europe, North America, and Asia. This emergence has been attributed to multiple and interactive drivers including changes in climate, land use, abundance of key hosts, and people's behaviors affecting the probability of human exposure to infected ticks. In this forum paper, we focus on how land use changes have shaped the eco-epidemiology of Ixodes scapularis-borne pathogens, in particular the Lyme disease spirochete Borrelia burgdorferi sensu stricto in the eastern United States. We use this as a model system, addressing other tick-borne disease systems as needed to illustrate patterns or processes. We first examine how land use interacts with abiotic conditions (microclimate) and biotic factors (e.g., host community composition) to influence the enzootic hazard, measured as the density of host-seeking I. scapularis nymphs infected with B. burgdorferi s.s. We then review the evidence of how specific landscape configuration, in particular forest fragmentation, influences the enzootic hazard and disease risk across spatial scales and urbanization levels. We emphasize the need for a dynamic understanding of landscapes based on tick and pathogen host movement and habitat use in relation to human resource provisioning. We propose a coupled natural-human systems framework for tick-borne diseases that accounts for the multiple interactions, nonlinearities and feedbacks in the system and conclude with a call for standardization of methodology and terminology to help integrate studies conducted at multiple scales.

The Contribution of Wildlife Hosts to the Rise of Ticks and Tick-Borne Diseases in North America

Wildlife vertebrate hosts are integral to enzootic cycles of tick-borne pathogens, and in some cases have played key roles in the recent rise of ticks and tick-borne diseases in North America. In this forum article, we highlight roles that wildlife hosts play in the maintenance and transmission of zoonotic, companion animal, livestock, and wildlife tick-borne pathogens. We begin by illustrating how wildlife contribute directly and indirectly to the increase and geographic expansion of ticks and their associated pathogens. Wildlife provide blood meals for tick growth and reproduction; serve as pathogen reservoirs; and can disperse ticks and pathogens-either through natural movement (e.g., avian migration) or through human-facilitated movement (e.g., wildlife translocations and trade). We then discuss opportunities to manage tick-borne disease through actions directed at wildlife hosts. To conclude, we highlight key gaps in our understanding of the ecology of tick-host interactions, emphasizing that wildlife host communities are themselves a very dynamic component of tick-pathogen-host systems and therefore complicate management of tick-borne diseases, and should be taken into account when considering host-targeted approaches. Effective management of wildlife to reduce tick-borne disease risk further requires consideration of the 'human dimensions' of wildlife management. This includes understanding the public's diverse views and values about wildlife and wildlife impacts-including the perceived role of wildlife in fostering tick-borne diseases. Public health agencies should capitalize on the expertise of wildlife agencies when developing strategies to reduce tick-borne disease risks.

Lake Michigan insights from island studies: the roles of chipmunks and coyotes in maintaining Ixodes scapularis and Borrelia burgdorferi in the absence of white-tailed deer

Deer management (e.g., reduction) has been proposed as a tool to reduce the acarological risk of Lyme disease. There have been few opportunities to investigate Ixodes scapularis (blacklegged tick) and Borrelia burgdorferi sensu stricto dynamics in the absence of white-tailed deer (Odocoileus virginianus) in midwestern North America. A pair of islands in Lake Michigan presented a unique opportunity to study the role of alternative hosts for the adult stage of the blacklegged tick for maintaining a tick population as a deer herd exists on North Manitou Island but not on South Manitou Island, where coyotes (Canis latrans) and hares (Lepus americanus) are the dominant medium mammals. Additionally, we were able to investigate the maintenance of I. scapularis and B. burgdorferi in small mammal communities on both islands, which were dominated by eastern chipmunks (Tamias striatus). From 2011 to 2015, we surveyed both islands for blacklegged ticks by drag cloth sampling, bird mist netting, and small and medium-sized mammal trapping. We assayed questing ticks, on-host ticks, and mammal biopsies for the Lyme disease pathogen, B. burgdorferi. We detected all three life stages of the blacklegged tick on both islands. Of the medium mammals sampled, no snowshoe hares (Lepus americanus, 0/23) were parasitized by adult blacklegged ticks, but 2/2 coyotes (Canis latrans) sampled on South Manitou Island in 2014 were parasitized by adult blacklegged ticks, suggesting that coyotes played a role in maintaining the tick population in the absence of deer. We also detected I. scapularis ticks on passerine birds from both islands, providing support that birds contribute to maintaining as well as introducing blacklegged ticks and B. burgdorferi to the islands. We observed higher questing adult and nymphal tick densities, and higher B. burgdorferi infection prevalence in small mammals and in adult ticks on the island with deer as compared to the deer-free island. On the islands, we also found that 25% more chipmunks were tick-infested than mice, fed more larvae and nymphs relative to their proportional abundance compared to mice, and thus may play a larger role compared to mice in the maintenance of B. burgdorferi. Our investigation demonstrated that alternative hosts could maintain a local population of blacklegged ticks and an enzootic cycle of the Lyme disease bacterium in the absence of white-tailed deer. Thus, alternative adult blacklegged tick hosts should be considered when investigating deer-targeted management tools for reducing tick-borne disease risk, especially when the alternative host community may be abundant and diverse.

What is the real number of Lyme disease cases in Canada?

BACKGROUND

Lyme disease is emerging in Canada due to expansion of the range of the tick vector Ixodes scapularis from the United States. National surveillance for human Lyme disease cases began in Canada in 2009. Reported numbers of cases increased from 144 cases in 2009 to 2025 in 2017. It has been claimed that few (< 10%) Lyme disease cases are reported associated with i) supposed under-diagnosis resulting from perceived inadequacies of serological testing for Lyme disease, ii) expectation that incidence in Canadian provinces and neighbouring US states should be similar, and iii) analysis of serological responses of dogs to the agent of Lyme disease, Borrelia burgdorferi. We argue that performance of serological testing for Lyme disease is well studied, and variations in test performance at different disease stages are accounted for in clinical diagnosis of Lyme disease, and in surveillance case definitions. Extensive surveillance for tick vectors has taken place in Canada providing a clear picture of the emergence of risk in the Canadian environment. This surveillance shows that the geographic scope of I. scapularis populations and Lyme disease risk is limited but increasing in Canada. The reported incidence of Lyme disease in Canada is consistent with this pattern of environmental risk, and the differences in Lyme disease incidence between US states and neighbouring Canadian provinces are consistent with geographic differences in environmental risk. Data on serological responses in dogs from Canada and the US are consistent with known differences in environmental risk, and in numbers of reported Lyme disease cases, between the US and Canada.

CONCLUSION

The high level of consistency in data from human case and tick surveillance, and data on serological responses in dogs, suggests that a high degree of under-reporting in Canada is unlikely. We speculate that approximately one third of cases are reported in regions of emergence of Lyme disease, although prospective studies are needed to fully quantify under-reporting. In the meantime, surveillance continues to identify and track the ongoing emergence of Lyme disease, and the risk to the public, in Canada.

Integrated Control of Nymphal Ixodes scapularis: Effectiveness of White-Tailed Deer Reduction, the Entomopathogenic Fungus Metarhizium anisopliae, and Fipronil-Based Rodent Bait Boxes

Pathogens transmitted by ticks are the leading cause of arthropod-associated human diseases in the United States and managing the risk of exposure to potentially infected ticks is of vital public health importance. A 3-year integrated tick management program to control blacklegged ticks, Ixodes scapularis, the primary vector for the pathogenic agents of Lyme disease, human anaplasmosis, and babesiosis, was implemented in the town of Redding in southwestern Connecticut beginning in 2013. Combinations of white-tailed deer, Odocoileus virginianus, reduction, area application of the entomopathogenic fungus Metarhizium anisopliae, and fipronil-based rodent bait boxes were evaluated for their ability to reduce nymphal I. scapularis over 3 years. Interference from local hunters prevented sufficient, sustained deer removal previously reported to negatively impact I. scapularis abundances (i.e., <5 deer/km²). The combination of fipronil-based bait boxes and broadcast application of M. anisopliae had the most impact of any treatment combination; questing nymphs were reduced 78-95% within each year and Borrelia burgdorferi-infected questing nymphal I. scapularis encounter potential was reduced by 66% as compared with no treatment in the third year of the study. A combination of the broadcast application of M. anisopliae and small rodent-targeted fipronil-based bait boxes is an effective low-toxicity integrated approach that significantly reduced encounters with B. burgdorferi-infected questing nymphal I. scapularis on individual properties.

Evidence for Personal Protective Measures to Reduce Human Contact With Blacklegged Ticks and for Environmentally Based Control Methods to Suppress Host-Seeking Blacklegged Ticks and Reduce Infection with Lyme Disease Spirochetes in Tick Vectors and Rodent Reservoirs

In the 1980s, the blacklegged tick, Ixodes scapularis Say, and rodents were recognized as the principal vector and reservoir hosts of the Lyme disease spirochete Borrelia burgdorferi in the eastern United States, and deer were incriminated as principal hosts for I. scapularis adults. These realizations led to pioneering studies aiming to reduce the risk for transmission of B. burgdorferi to humans by attacking host-seeking ticks with acaricides, interrupting the enzootic transmission cycle by killing immatures infesting rodent reservoirs by means of acaricide-treated nesting material, or reducing deer abundance to suppress tick numbers. We review the progress over the past three decades in the fields of: 1) prevention of human-tick contact with repellents and permethrin-treated clothing, and 2) suppression of I. scapularis and disruption of enzootic B. burgdorferi transmission with environmentally based control methods. Personal protective measures include synthetic and natural product-based repellents that can be applied to skin and clothing, permethrin sprays for clothing and gear, and permethrin-treated clothing. A wide variety of approaches and products to suppress I. scapularis or disrupt enzootic B. burgdorferi transmission have emerged and been evaluated in field trials. Application of synthetic chemical acaricides is a robust method to suppress host-seeking I. scapularis ticks within a treated area for at least 6-8 wk. Natural product-based acaricides or entomopathogenic fungi have emerged as alternatives to kill host-seeking ticks for homeowners who are unwilling to use synthetic chemical acaricides. However, as compared with synthetic chemical acaricides, these approaches appear less robust in terms of both their killing efficacy and persistence. Use of rodent-targeted topical acaricides represents an alternative for homeowners opposed to open distribution of acaricides to the ground and vegetation on their properties. This host-targeted approach also provides the benefit of the intervention impacting the entire rodent home range. Rodent-targeted oral vaccines against B. burgdorferi and a rodent-targeted antibiotic bait have been evaluated in laboratory and field trials but are not yet commercially available. Targeting of deer-via deer reduction or treatment of deer with topical acaricides-can provide area-wide suppression of host-seeking I. scapularis. These two deer-targeted approaches combine great potential for protection that impacts the entire landscape with severe problems relating to public acceptance or implementation logistics. Integrated use of two or more methods has unfortunately been evaluated in very few published studies, but additional field evaluations of integrated tick and pathogen strategies are underway.

Tick species, tick-borne pathogens and symbionts in an insular environment off the coast of Western France

Insular environments provide ideal natural conditions to study disease ecology, especially emerging diseases, due to clear differentiation between local and long-distance transmission. Such environments are of particular interest regarding tick-borne pathogens (TBP), since animal exchange with the mainland (along with any ticks they carry) is limited, and because such locations could lie on migratory routes for birds carrying ticks. Therefore both tick species and TBP may display different prevalence than those observed on the continent. As such, an epidemiological survey was performed on Belle-Ile-en-Mer, an island off the coast of Western France, in order to estimate the prevalence of tick species and the microorganisms they carried. Three tick species, Dermacentor marginatus, D. reticulatus, and Haemaphysalis punctata were collected at five different sites in 2010 and 2011. All ticks were tested for pathogen's and symbiont's DNA by (i) PCR for Anaplasma spp., Borrelia spp., Rickettsia spp.; (ii) real-time PCR for Francisella tularensis, Francisella-like endosymbionts (FLE) and Coxiella spp. and (iii) PCR-RLB for Babesia-Theileria spp. Pathogen DNA detected in D. marginatus including Borrelia spp. (18%), Rickettsia spp. (13%) which was identified as R. slovaca, Babesia spp. (8%), and Theileria spp. (1%). Pathogens detected in D. reticulatus including Rickettsia spp. (31%) identified as R. raoulti, Francisella-like endosymbiont (86%), and Babesia spp (21%). Pathogens detected in H. punctata including Rickettsia spp. (1%) identified as R. aeschlimannii, FLE (0.4%), Babesia spp. (18%), and Theileria spp. (7%). Anaplasma spp., F. tularensis, or Coxiella spp. were not detected in any of the collected ticks. This study represents the first epidemiological survey of the insular Belle-Ile-en-Mer environment. It demonstrated the presence of expected pathogens, consistent with reports from island veterinarians or physicians, as well as unexpected pathogens, raising questions about their potential introduction through infected animals and/or their dispersion by migratory birds.

Will Culling White-Tailed Deer Prevent Lyme Disease?

White-tailed deer play an important role in the ecology of Lyme disease. In the United States, where the incidence and geographic range of Lyme disease continue to increase, reduction of white-tailed deer populations has been proposed as a means of preventing human illness. The effectiveness of this politically sensitive prevention method is poorly understood. We summarize and evaluate available evidence regarding the effect of deer reduction on vector tick abundance and human disease incidence. Elimination of deer from islands and other isolated settings can have a substantial impact on the reproduction of blacklegged ticks, while reduction short of complete elimination has yielded mixed results. To date, most studies have been conducted in ecologic situations that are not representative to the vast majority of areas with high human Lyme disease risk. Robust evidence linking deer control to reduced human Lyme disease risk is lacking. Currently, there is insufficient evidence to recommend deer population reduction as a Lyme disease prevention measure, except in specific ecologic circumstances.

Recent and rapid population growth and range expansion of the Lyme disease tick vector, Ixodes scapularis, in North America

Migration is a primary force of biological evolution that alters allele frequencies and introduces novel genetic variants into populations. Recent migration has been proposed as the cause of the emergence of many infectious diseases, including those carried by blacklegged ticks in North America. Populations of blacklegged ticks have established and flourished in areas of North America previously thought to be devoid of this species. The recent discovery of these populations of blacklegged ticks may have resulted from either in situ growth of long-established populations that were maintained at very low densities or by migration and colonization from established populations. These alternative evolutionary hypotheses were investigated using Bayesian phylogeographic approaches to infer the origin and migratory history of recently detected blacklegged tick populations in the Northeastern United States. The data and results indicate that newly detected tick populations are not the product of in situ population growth from a previously established population but from recent colonization resulting in a geographic range expansion. This expansion in the geographic range proceeded primarily through progressive and local migration events from southern populations to proximate northern locations although long-distance migration events were also detected.

Quantitative factors proposed to influence the prevalence of canine tick-borne disease agents in the United States

The Companion Animal Parasite Council hosted a meeting to identify quantifiable factors that can influence the prevalence of tick-borne disease agents among dogs in North America. This report summarizes the approach used and the factors identified for further analysis with mathematical models of canine exposure to tick-borne pathogens.

Blood feeding on large grazers affects the transmission of Borrelia burgdorferi sensu lato by Ixodes ricinus

The presence of Ixodes ricinus and their associated Borrelia infections on large grazers was investigated. Carcases of freshly shot red deer, mouflon and wild boar were examined for the presence of any stage of I. ricinus. Questing ticks were collected from locations where red deer and wild boar are known to occur. Presence of Borrelia burgdorferi s.l. DNA was examined in a fraction of the collected ticks. Larvae, nymphs and adult ticks were found on the three large grazers. Red deer had the highest tick burden, with many of the nymphs and adult females attached for engorgement. Most larvae had not attached. The mean number of ticks on the animals varied from 13 to 67. Ticks were highly aggregated amongst the animals: some animals had no ticks, while others had high numbers. Larvae and nymphs were mostly found on the ears, while adult ticks were attached to the axillae. The Borrelia infection rate of questing nymphs was 8.5%. Unengorged wandering nymphs on deer had a Borrelia infection rate of 12.5%, while only 0.9% of feeding nymphs carried a Borrelia infection. The infection rate of unengorged adult male ticks was 4.5%, and that of feeding female ticks was 0.7%. The data suggest that ticks feeding on red deer and wild boar lose their Borrelia infections. The implications of the results are discussed with respect to Borrelia epidemiology and maintenance of a Borrelia reservoir as well as the role of reproductive hosts for Ixodes ricinus.