Over the last 20 years, Lyme disease has grown to become the most common vector-borne disease affecting Americans. Spread in the eastern U.S. primarily by the bite of Ixodes scapularis, the black-legged tick, the disease affects an estimated 329,000 Americans per year. Originally confined to New England, it has since spread across much of the east coast and has become endemic in Virginia. Since 2010 the state has averaged 1200 cases per year, with 200 annually in the New River Health District (NRHD), the location of our study. Efforts to geographically model Lyme disease primarily focus on landscape and climatic variables. The disease depends highly on the survival of the tick vector, and white-footed mouse, the primary reservoir. Both depend on the existence of forest-herbaceous edge-habitats, as well as warm summer temperatures, mild winter lows, and summer wetness. While many studies have investigated the effect of forest fragmentation on Lyme, none have made use of high-resolution land cover data to do so at the peridomestic level. To fill this knowledge gap, we made use of the Virginia Geographic Information Network’s 1-meter land cover dataset and identified forest-herbaceous edge-habitats for the NRHD. We then calculated the density of these edge-habitats at 100, 200 and 300-meter radii, representing the peridomestic environment. We also calculated the density of <2-hectare forest patches at the same distance thresholds. To avoid confounding from climatic variation, we also calculated mean summer temperatures, total summer rainfall, and number of consecutive days below freezing of the prior winters. Adding to these data, elevation, terrain shape index, slope, and aspect, and including lags on each of our climatic variables, we created environmental niche models of Lyme in the NRHD. We did so using both Boosted Regression Trees (BRT) and Maximum Entropy (MaxEnt) modeling, the two most common niche modeling algorithms in the field today. We found that Lyme is strongly associated with higher density of developed-herbaceous edges within 100-meters from the home. Forest patch density was also significant at both 100-meter and 300-meter levels. This supports the notion that the fine scale peridomestic environment is significant to Lyme outcomes, and must be considered even if one were to account for fragmentation at a wider scale, as well as variations in climate and terrain. / M.S. / Lyme disease is the most common vector-borne disease in the United States today. Infecting about 330,000 Americans per year, the disease continues to spread geographically. Originally found only in New England, the disease is now common in Virginia. The New River Health District, where we did our study, sees over 200 cases per year. Lyme disease is mostly spread by the bite of the black-legged tick. As such we can predict where Lyme cases might be found if we understand the environmental needs of these ticks. The ticks themselves depend on warm summer temperatures, mild winter lows, and summer wetness. But they are also affected by forest fragmentation which drives up the population of white-footed mice, the tick’s primary host. The mice are particularly fond of the interface between forests and open fields. These edge habitats provide food and cover for the mice, and in turn support a large population of ticks. Many existing studies have demonstrated this link, but all have done so across broad scales such as counties or census tracts. To our knowledge, no such studies have investigated forest fragmentation near the home of known Lyme cases. To fill this gap in our knowledge, we made use of high-resolution forest cover data to identify forest-field edge habitats and small isolated forest patches. We then calculated the total density of both within 100, 200 and 300 meters of the homes of known Lyme cases, and compared these to values from non-cases using statistical modeling. We also included winter and summer temperatures, rainfall, elevation, slope, aspect, and terrain shape. We found that a large amount of forest-field edges within 100 meters of a home increases the risk of Lyme disease to residents of that home. The same can be said for isolated forest patches. Even after accounting for all other variables, this effect was still significant. This information can be used by health departments to predict which neighborhoods may be most at risk for Lyme. They can then increase surveillance in those areas, warn local doctors, or send out educational materials.

Depuis les années 90, les études réalisées au Canada ont permis d’identifier de nouvelles zones endémiques de l’agent de la maladie de Lyme, Borrelia burgdorferi, ou de sa tique vectrice, Ixodes scapularis. Ces régions représentent des zones privilégiées pour étudier le cycle de transmission dans son contexte environnemental. L’objectif principal de ce projet est d’étudier les relations spirochètes – tiques - hôtes et les facteurs environnementaux impliqués dans le cycle de transmission à partir des données du vecteur et de l’agent pathogène recueilli dans le Sud-Ouest du Québec de 2007 à 2008. Tout d’abord sera décrite la saisonnalité des tiques et des associations entre le vecteur et les hôtes rongeurs capturés. En effet, l’identification de la saisonnalité spécifique à chaque stade de la tique I. scapularis permet d’établir quels seront les mois propices pour effectuer les futures collectes de tiques. La saisonnalité synchrone des tiques immatures en quête peut également être un indicateur de la nature ou des souches de B. burgdorferi retrouvées. L’association des tiques immatures à différentes espèces ou à différentes classes d’hôtes (c.-à-d. âge, sexe, statut reproductif) a également été explorée. Nos résultats montrent que les souris du genre Peromyscus, principalement les mâles adultes, contribuent significativement à la survie et au développement du complexe I. scapularis - B. burgdorferi. Les tamias et les écureuils contribuent aussi à la survie et au développement des populations de la tique I. scapularis. Ensuite les associations entre le vecteur et les hôtes cervidés ont été examinées en tenant compte des facteurs environnementaux associés à leur niveau d’infestation. Ceci a permis d’évaluer l’utilisation des cerfs à titre de sentinelles pour le vecteur et les agents pathogènes. D’après nos résultats, bien qu’ils soient des sentinelles efficaces pour détecter Anaplasma phagocytophilum, les cerfs semblent des sentinelles inefficaces pour détecter les zones d’établissement du complexe I. scapularis-B. burgdorferi. Enfin, une analyse de l’impact de la diversité des hôtes et de l’habitat sur l’abondance de la tique I. scapularis et la prévalence de B. burgdorferi a été effectuée et ce, en tenant compte d’autres facteurs environnementaux. Ces analyses ont permis de déterminer les facteurs critiques pour l’établissement du complexe I. scapularis – B. burgdorferi et d’explorer la contribution relative de diverses espèces d’hôtes. D’après nos études, la diversité de la communauté d’hôte et la diversité de l’habitat influencent le complexe I. scapularis - B. burgdorferi. De plus, le climat (la température et les précipitations) joue un rôle significatif dans l’établissement, la survie et le développement des populations d’I. scapularis. Ce projet de recherche a permis d’explorer et d’identifier divers facteurs environnementaux biotiques et abiotiques influençant l’établissement du complexe I. scapularis - B. burgdorferi dans le Sud-Ouest du Québec. Ceux-ci pourraient être utilisés à titre d’indicateurs environnementaux du risque de la maladie de Lyme au Québec et possiblement ailleurs au Canada. / Since the 90s in Canada, studies have identified new endemic areas for the agent of Lyme disease, Borrelia burgdorferi and the tick vector, Ixodes scapularis. These newly endemic areas for complex I. scapularis - B. burgdorferi are prime areas to study the transmission cycle in its environmental context. The main objective of this project is to study the spirochete-tick-host relationships and environmental factors involved in the transmission cycle from the data of the vector and the pathogen collected in southwestern Quebec, 2007 to 2008. First, a description of the seasonality of ticks and associations between the vector and captured rodent hosts was performed. The identification of specific seasonality at each stage of the tick I. scapularis establishes months conducive to make the future collections of ticks. Synchronous seasonality of questing immature ticks may also be an indicator of the nature or strain of B. burgdorferi found. In addition, the association of immature ticks in different species or different classes of hosts (i.e. age, sex, reproductive status) was explored. The Peromyscus mice and adult males in particular contributed significantly to the survival and development of complex I. scapularis-B. burgdorferi. Chipmunks and squirrels also contributed to the survival and development of I. scapularis populations. Second, the associations between vector and examined deer was described taking into account the environmental factors associated with the level of infestation and the use of deer as sentinels for the vector and the pathogen was evaluated. According to our results, the deer are effective sentinels to detect Anaplasma phagocytophilum, but seem ineffective or imprecise to detect endemic areas for complex I. scapularis-B. burgdorferi. Finally, an analysis of the impact of the host diversity and habitat on the abundance of I. scapularis and prevalence of B. burgdorferi considering other environmental factors was performed. These analyzes were used to determine the critical factors in the establishment of complex I. scapularis-B. burgorferi and explore the relative contribution of various host species. According to our studies, the diversity of the host community and habitat influences the complex I. scapularis-B. burgdorferi. On the other hand, the climate (temperature and precipitation) plays a significant role in the establishment, survival and development of the I. scapularis populations. This study allowed us to explore and identify various biotic and abiotic environmental factors influencing the establishment of complex I. scapularis-B. burgdorferi in southwestern Quebec. These environmental factors could be used as environmental indicators of the risk of Lyme disease in Quebec and possibly elsewhere in Canada.

No description available.

La maladie de Lyme est émergente au Canada; le risque engendré par cette maladie vient en partie de la ténacité de son vecteur et des méthodes limitées pour réduire son abondance dans l’environnement. Actuellement, peu de moyens de prévention visent de manière efficace et sécuritaire le réservoir principal de la bactérie responsable de la maladie, la souris à patte blanche Peromyscus leucopus. L’objectif de ce projet était d’évaluer l’efficacité des isoxazolines, une nouvelle classe d’antiparasitaire, lorsqu’administré sous forme d’appâts oraux aux micromammifères résidents d’un site endémique pour la maladie de Lyme. Les appâts furent distribués lors de l’été 2018 et 2019, sur les terrains choisis du parc national des Mille-Îles, en Ontario. La capture de micromammifères, en terrain traité et non traité, nous permit d’évaluer l’infestation (nombre de tiques par souris) du réservoir Peromyscus alors que l’effet du traitement sur la densité de tiques dans l’environnement fut estimé par la technique de flanelle. L’impact de la molécule d’isoxazoline employée (sarolaner versus fluralaner), de la biodiversité et du type d’environnement (caractéristiques de la forêt, température, humidité) fut également évalué. Des modèles linéaires mixtes binomiale négative furent composés pour déterminer l’impact de chacune des variables mesurées et du traitement sur les variables dépendantes, soit le nombre de tiques sur les souris capturées et la densité de nymphes dans l’environnement. Après deux étés de traitement, les souris capturées sur les microsites traités furent significativement moins infestées que les souris capturées sur les microsites contrôles pour 3 des 5 sites étudiés. Par contre, aucune diminution significative du nombre de nymphes dans l’environnement ne fut observée, probablement dû à la courte durée du devis d’étude. La densité de nymphes dans l’environnement variait toutefois en fonction de l’année d’échantillonnage et était positivement corrélée avec la biodiversité au niveau du microsite. Le nombre de tiques sur Peromyscus spp. était associé au sexe (les mâles étant plus infesté) et à la taille de l’animal, au mois et à l’année de la capture, à une forte densité de larves dans l’environnement et au traitement effectué sur le microsite de capture. Le fluralaner se montra plus efficace à réduire l’infestation moyenne des rongeurs. Cette étude fut la première à étudier l’utilisation de saronaler oral chez le réservoir principal de l’agent de la maladie de Lyme en milieu naturel. L’effet du traitement chez les micromammifères est prometteur, mais son efficacité pour réduire la densité de tiques dans l’environnement reste à confirmer. / Lyme disease is the most common vector-borne disease in North America; the risk caused by the disease is partly due to its tick vector’s tenacity and limited number of approaches to reduce its abundance in the environment. Few existing methods efficiently and safely target the principal host for the bacteria, white-footed mice Peromyscus leucopus.The objective of this thesis was to evaluate the efficacy of a new family of antiparasitic drug, isoxazolines, when passively administered as an oral bait to micromammals in endemic site for Lyme disease. Oral baits were distributed during the summer of 2018 and 2019 on five selected sites in the Thousand Islands National Park. Density of ticks in the environment was estimated using drag sampling while small mammal trapping allowed biodiversity and infestation (number of ticks per mouse) to be assess. Impact of isoxazoline used (sarolaner or fluralaner), biodiversity and characteristics of environment (type of forests, temperature, humidity) were also evaluated. Linear mixed models were fitted to determine the impact of measured variables and treatment on infestation level and density of questing nymphs. Results show a significant reduction in tick load for mice captured on treatment plots compared to control plots for 3 out of 5 sites. However, we did not observe a significant reduction in the density of questing nymphs, probably due to the limited duration of the study. Density of nymphs followed interannual variation and was best explained by humidity levels at the time of sampling and plot-level host biodiversity. Peromyscus spp. infestation was linked to the sex (male being more infested) and body length of the mice, high density of questing larvae, year and month of capture and treatment applied to the microsite. Fluralaner showed to be more efficient at reducing mice average tick load. This study was the first to use oral sarolaner to treat the most important reservoir for the Lyme disease agent in the environment. Our protocol did not significantly reduce questing nymphs in the environment for the duration of this study but could potentially diminish Lyme disease human risk with long term use through reduced Peromyscus infestation.

Lyme disease is an emerging tick-borne illness in Canada, with human case numbers increasing 15- to 20-fold since Lyme disease became nationally notifiable in 2009 until the present. In Ontario, Canada's largest province by population, average Lyme disease incidence across the province is similar to that of national estimates. However, in eastern Ontario, which is near tick endemic regions in the northeastern Unites States, Lyme disease incidence is disproportionately higher compared to the rest of the province. The objectives of this thesis are to identify environmental Lyme disease risk areas in Ontario, to explore spatiotemporal trends in Lyme disease emergence, and to identify neighbourhood-level socioecological risk factors for Lyme disease. In addition, this thesis also aims to assess the risk of other tick-borne illnesses that are transmitted by the blacklegged tick, Ixodes scapularis, which is also the main vector for Lyme disease in Canada. Using maximum entropy species distribution modelling to correlate blacklegged tick occurrence data with environmental variables, predictive risk models for I. scapularis and the Lyme disease pathogen, Borrelia burgdorferi, were developed. The model prediction was used to classify low and high environment risk areas and, using a case-control epidemiological study, we assessed that residence in risk areas was a strong predictor of Lyme disease. However, this relationship was modulated by socioecological factors linked to higher overall rurality of the locality of home residence. Spatial cluster analyses further revealed that human Lyme disease cases clustered in regions with the high numbers of reported B. burgdorferi-infected ticks in the environment. Many individuals residing in large metropolitan regions, like the City of Ottawa, reported tick exposures outside their public health unit of residence; however, local clusters of Lyme disease were also detected in suburban regions near conservation areas, trails, and urban woodlands. The prevalence of other tick-borne pathogens was low, although several pathogens of public health significance including Borrelia miyamotoi and Anaplasma phagocytophilum were detected at multiple sites surveyed for ticks between 2017-2021. Overall, this thesis identify patterns in Lyme disease emergence (and potentially other tick-borne illnesses), defines environmental risk areas for Lyme disease in Ontario, and highlights important socioecological risk factors for Lyme disease in eastern Ontario.

Cette thèse est une investigation de l'écologie et de l'épidémiologie spatiale fine de la tique à pattes noires (Ixodes scapularis) et du risque associé aux pathogènes transmis par cette tique dans une forêt du sud du Québec, au Canada. Sous l’influence de changements climatiques et environnementaux, la répartition spatiale de cette tique s’étend actuellement à travers la province, et son abondance augmente dans la plupart des régions. Il en résulte une préoccupation croissante en matière de santé publique liée à l'émergence de maladies transmises par les tiques (MTT) dans la province. Ainsi, plusieurs besoins de recherche ont vu le jour, y compris l’amélioration de la compréhension des facteurs dictant où et quand le risque émergera, et l’identification des composantes sur lesquelles les autorités régionales, locales et les individus pourraient agir afin réduire ce risque. Le site d’étude pour ce projet était le parc National du Mont-Saint-Bruno. De 2016 à 2018, à 32 sites répartis dans les habitats forestiers du parc, les tiques ont été collectées par la technique de la flanelle, la communauté d’hôtes de la tique a été inventoriée (grands et petits mammifères, et oiseaux nicheurs) et les micro-habitats ont été caractérisés (en termes de structure, de composition et de conditions microclimatiques). La densité des tiques dans la zone d’étude était particulièrement élevée par rapport aux autres régions environnantes. Les analyses spatiales ont montré des patrons d’abondance des tiques, persistants sur trois ans, avec un effet significatif des conditions locales de températures et d’humidité relatives. Un effet significatif de la densité du stade de développement précédent lors de l’année précédente a également été noté, suggérant une dispersion lente des tiques par les hôtes et une dynamique d’invasion caractérisée par plusieurs évènements d’introduction et d’expansion opérant à une échelle locale. En 2017 et 2018, un dispositif d’échantillonnage plus extensif a visé la communauté d’hôtes des stades immatures d’I. scapularis, afin de documenter le rôle de ces espèces dans la circulation des agents pathogènes. 849 oiseaux nicheurs appartenant à 50 espèces et 694 petits mammifères appartenant à 4 espèces ont été examinés pour la présence des tiques et des pathogènes. Les souris à pattes blanches (Peromyscus leucopus) contribuaient à la majorité (80%) des cas d’infection des nymphes par Borrelia burgdorferi dans l’échantillon, alors que les 20% restants étaient attribuables à des oiseaux. Ce résultat confirme la proposition de certains auteurs à savoir que l’importance des hôtes alternatifs (autres que P. leucopus) aient été sous-estimée dans les études précédentes, et souligne l’importance de poursuivre les travaux pour documenter l’impact de ces hôtes dans l’épidémiologie des MTT. Finalement, la caractérisation des patrons de risque associés aux MTT dans la zone d’étude a été complétée par un échantillonnage de l’intensité d’utilisation des sentiers par les visiteurs du parc en 2017 et 2018. D’abord, les prélèvements de tiques dans l’environnement et sur les hôtes ont permis de détecter la présence de trois pathogènes représentant un risque de santé publique pour la population locale, soit en ordre du plus au moins prévalent : B. burgdorferi, Anaplasma phagocytophyllum et Borrelia miyamotoi. Ensuite, l’intégration des patrons spatiaux de l’utilisation du parc par les visiteurs a mis en évidence le rôle des facteurs comportementaux des utilisateurs et des attributs du paysage local dans la détermination des patrons de risque de contacts entre les visiteurs et les nymphes infectées par B. burgdorferi. Le risque de contact était associé à certaines périodes et zones de forte fréquentation du parc, mais pas aux indicateurs locaux de fragmentation de l'habitat, comme le suggèrent d'autres études. En outre, les zones où la densité de la couverture forestière et des points d'intérêt (infrastructures) étaient les plus élevés présentaient les niveaux de risque les plus élevés. Cette thèse contribue à l’avancement des connaissances fondamentales reliées à la biologie des tiques, aux relations écologiques entre ces ectoparasites et leurs hôtes et à l’écologie des pathogènes qu’elles transmettent. Ces connaissances trouveront de multiples applications concrètes, principalement dans le domaine de la santé publique où elles permettront notamment de parfaire les outils existants d’évaluation du risque et de prévention des MTT. En reliant l’écologie à la santé publique, cette thèse répond à un besoin de recherche et de développement d’expertise qui devient de plus en plus important dans le contexte actuel des changements climatiques et de l’émergence des maladies zoonotiques qui s’en trouvent facilitées au Canada. / This thesis is an investigation of the ecology and fine-scale spatial epidemiology of the blacklegged tick (Ixodes scapularis) and the risk associated with pathogens transmitted by this tick in a forest of southern Quebec, Canada. Under the influence of climate and environmental changes, the spatial distribution of this tick is currently expanding across the province, and its abundance is increasing in most regions. This has resulted in a growing public health threat associated with the emergence of tick-borne diseases (TBDs) in the province. Thus, several research needs have emerged, including improving understanding of the factors determining where and when risk will arise, and identifying what regional and local health authorities and individuals can do to reduce that risk. The study site for this project was Mont-Saint-Bruno National Park. From 2016 to 2018, at 32 sites distributed in the park's forest habitats, ticks were collected by drag sampling, the host community was inventoried (large and small mammals, and nesting birds), and microhabitats were characterized (in terms of structure, composition, and microclimatic conditions). The density of ticks in the study area was particularly high compared to other surrounding areas. Spatial analyses showed patterns of tick abundance, persistent over three years, with a significant effect of local microclimatic conditions (relative temperature and humidity). A significant effect of the density of the previous developmental stage in the previous year was also noted, suggesting slow host dispersal of ticks and invasion dynamics characterized by several introduction and expansion events operating at a local scale. In 2017 and 2018, a more extensive sampling scheme targeted the host community of immature stages of I. scapularis, to document the role of these species in pathogen circulation. 849 breeding birds belonging to 50 species and 694 small mammals belonging to 4 species were examined for the presence of ticks and pathogens. White-footed mice (Peromyscus leucopus) contributed to the majority (80%) of Borrelia burgdorferi nymph infections in the sample, while the remaining 20% were attributable to birds. This result confirms the suggestion by some authors that the importance of alternative hosts (other than P. leucopus) may have been underestimated in previous studies and underscores the importance of further work to document the impact of these hosts in the epidemiology of TBDs. Finally, characterization of risk patterns associated with TBDs in the study area was completed by sampling trail use by park visitors in 2017 and 2018. First, the analysis of ticks collected from the environment and on hosts demonstrated the presence of three pathogens representing a public health risk to the local population, in order from the most to the least prevalent: B. burgdorferi, Anaplasma phagocytophyllum and Borrelia miyamotoi. Second, integration of spatial patterns of visitor use of the park highlighted the role of visitor behaviour and local landscape attributes in determining patterns of risk of contact between visitors and B. burgdorferi-infected nymphs. Risk was associated with certain times and areas of increased park use, but not with local indicators of habitat fragmentation, in contrast with the results of previous studies. In addition, areas with the highest densities of forest cover and points of interest (infrastructure) had the highest levels of risk. This thesis contributes to the advancement of fundamental knowledge related to the biology of ticks, the ecological relationships between these ectoparasites and their hosts, and the ecology of the pathogens they transmit. This knowledge will have multiple applications, mainly in the field of public health, where it will allow the refinement of existing tools for risk assessment and prevention of TBDs. By linking ecology to public health, this thesis responds to a need for research and development of expertise that is becoming increasingly important in the current context of climate change and the emergence of zoonotic diseases that it facilitates in Canada.

No description available.

Little is understood about off-host behavior and ecology of immature Amblyomma maculatum Koch (Gulf Coast tick). A more complete understanding of this tick is essential to protect human and animal health. My research focused on seasonality and distribution of immatures in Mississippi, potential suitability of some insect and human hosts to larvae, and aspects of nymphal questing behavior. A single larva was collected (third off-host collection reported) when sampling A. maculatum habitat using a novel device. Collection of this larva in November expands the stage’s known seasonality and confirmed a prediction concerning seasonality of larval A. maculatum. Low frequency of immatures (8.3%) confirmed that they’re incredibly difficult to collect off-host. Nymphal collections peaked in March, and known seasonality was extended for both nymphs and adults. I examined known records, elucidating seasonality and distribution of A. maculatum in Mississippi. Either multiple generations per year or diapause are responsible for observed bi-modal distribution of immature collections. Additionally, I compiled the most extensive host record of immature A. maculatum in Mississippi and investigated seasonality patterns using USDA plant hardiness zones. I compiled the most complete record of ticks found on arthropods. Amblyomma americanum and A. maculatum were both confirmed to crawl onto arthropods, giving support to occasional, unintentional dispersal by phoresy. There was no conclusive evidence that larval A. maculatum feed on arthropods, however data supported feeding by larval A. americanum. These results have interesting implications regarding evolution of pathogens/endosymbionts. I provided the first evidence that larval A. maculatum can attach to humans. Rickettsia parkeri, a human pathogen transmitted by this species has recently been shown to be capable of transovarial transmission. Therefore, larval A. maculatum may provide another avenue of transmission. I have demonstrated that A. maculatum are difficult to collect off-host in part because they prefer to quest low to the ground. In choice studies, 5-cm-tall stems were most likely to be occupied by nymphs released into an array of stems. Low vapor pressure deficit encouraged questing, while higher VPD and warmer temperature increased questing height. These results may have implications in understanding host-seeking behavior in other tick species as well.