Ixodes scapularis density and Borrelia burgdorferi prevalence along a residential-woodland gradient in a region of emerging Lyme disease risk.

The environmental risk of Lyme disease, defined by the density of Ixodes scapularis ticks and their prevalence of Borrelia burgdorferi infection, is increasing across the Ottawa, Ontario region, making this a unique location to explore the factors associated with environmental risk along a residential-woodland gradient. In this study, we collected I. scapularis ticks and trapped Peromyscus spp. mice, tested both for tick-borne pathogens, and monitored the intensity of foraging activity by deer in residential, woodland, and residential-woodland interface zones of four neighbourhoods. We constructed mixed-effect models to test for site-specific characteristics associated with densities of questing nymphal and adult ticks and the infection prevalence of nymphal and adult ticks. Compared to residential zones, we found a strong increasing gradient in tick density from interface to woodland zones, with 4 and 15 times as many nymphal ticks, respectively. Infection prevalence of nymphs and adults together was 15 to 24 times greater in non-residential zone habitats. Ecological site characteristics, including soil moisture, leaf litter depth, and understory density, were associated with variations in nymphal density and their infection prevalence. Our results suggest that high environmental risk bordering residential areas poses a concern for human-tick encounters, highlighting the need for targeted disease prevention.

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.

The risk of contact between visitors and Borrelia burgdorferi-infected ticks is associated with fine-scale landscape features in a southeastern Canadian nature park.

BACKGROUND: Infectious diseases are emerging across temperate regions of the world, and, for some, links have been made between landscapes and emergence dynamics. For tick-borne diseases, public parks may be important exposure sites for people living in urbanized areas of North America and Europe. In most cases, we know more about the ecological processes that determine the hazard posed by ticks as disease vectors than we do about how human population exposure varies in urban natural parks. METHODS: In this study, infrared counters were used to monitor visitor use of a public natural park in southern Quebec, Canada. A risk index representing the probability of encounters between humans and infected vectors was constructed. This was done by combining the intensity of visitor trail use and the density of infected nymphs obtained from field surveillance. Patterns of risk were examined using spatial cluster analysis. Digital forest data and park infrastructure data were then integrated using spatially explicit models to test whether encounter risk levels and its components vary with forest fragmentation indicators and proximity to park infrastructure. RESULTS: Results suggest that, even at a very fine scales, certain landscape features and infrastructure can be predictors of risk levels. Both visitors and Borrelia burgdorferi-infected ticks concentrated in areas where forest cover was dominant, so there was a positive association between forest cover and the risk index. However, there were no associations between indicators of forest fragmentation and risk levels. Some high-risk clusters contributed disproportionately to the risk distribution in the park relative to their size. There were also two high-risk periods, one in early summer coinciding with peak nymphal activity, and one in early fall when park visitation was highest. CONCLUSIONS: Here, we demonstrate the importance of integrating indicators of human behaviour visitation with tick distribution data to characterize risk patterns for tick-borne diseases in public natural areas. Indeed, understanding the environmental determinants of human-tick interactions will allow organisations to deploy more effective risk reduction interventions targeted at key locations and times, and improve the management of public health risks associated with tick-borne diseases in public spaces.

Home range overlap between small Indian mongooses and free roaming domestic dogs in Puerto Rico: implications for rabies management.

The small Indian mongoose (Urva auropunctata) is the primary terrestrial wildlife rabies reservoir on at least four Caribbean islands, including Puerto Rico. In Puerto Rico, mongooses represent a risk to public health, based on direct human exposure and indirectly through the transmission of rabies virus to domestic animals. To date, the fundamental ecological relationships of space use among mongooses and between mongooses and domestic animals remain poorly understood. This study is the first to report mongoose home range estimates based on GPS telemetry, as well as concurrent space use among mongooses and free roaming domestic dogs (FRDD; Canis lupus familiaris). Mean (± SE) home range estimates from 19 mongooses in this study (145 ± 21 ha and 60 ± 14 ha for males and females, respectively) were greater than those reported in prior radiotelemetry studies in Puerto Rico. At the scale of their home range, mongooses preferentially used dry forest and shrubland areas, but tended to avoid brackish water vegetation, salt marshes, barren lands and developed areas. Home ranges from five FRDDs were highly variable in size (range 13-285 ha) and may be influenced by availability of reliable anthropogenic resources. Mongooses displayed high home range overlap (general overlap index, GOI = 82%). Home range overlap among mongooses and FRDDs was intermediate (GOI = 50%) and greater than home range overlap by FRDDs (GOI = 10%). Our results provide evidence that space use by both species presents opportunities for interspecific interaction and contact and suggests that human provisioning of dogs may play a role in limiting interactions between stray dogs and mongooses.

Future land-use change predictions using Dyna-Clue to support mosquito-borne disease risk assessment.

Mosquitoes are known vectors for viral diseases in Canada, and their distribution is driven by climate and land use. Despite that, future land-use changes have not yet been used as a driver in mosquito distribution models in North America. In this paper, we developed land-use change projections designed to address mosquito-borne disease (MBD) prediction in a 38 761 km2 area of Eastern Ontario. The landscape in the study area is marked by urbanization and intensive agriculture and hosts a diverse mosquito community. The Dyna-CLUE model was used to project land-use for three time horizons (2030, 2050, and 2070) based on historical trends (from 2014 to 2020) for water, forest, agriculture, and urban land uses. Five scenarios were generated to reflect urbanization, agricultural expansion, and natural areas. An ensemble of thirty simulations per scenario was run to account for land-use conversion uncertainty. The simulation closest to the average map generated was selected to represent the scenario. A concordance matrix generated using map pair analysis showed a good agreement between the simulated 2020 maps and 2020 observed map. By 2050, the most significant changes are predicted to occur mainly in the southeastern region's rural and forested areas. By 2070, high deforestation is expected in the central west. These results will be integrated into risk models predicting mosquito distribution to study the possibility of humans' increased exposure risk to MBDs.

Low levels of genetic differentiation and structure in red fox populations in Eastern Canada and implications for Arctic fox rabies propagation potential.

Rabies is a lethal zoonosis present in most parts of the world which can be transmitted to humans through the bite from an infected mammalian reservoir host. The Arctic rabies virus variant (ARVV) persists mainly in populations of Arctic foxes (Vulpes lagopus), and to a lesser extent in red fox populations (Vulpes vulpes). Red foxes are thought to be responsible for sporadic southward movement waves of the ARVV outside the enzootic area of northern Canada. In this study, we wanted to investigate whether red foxes displayed notable levels of genetic structure across the Quebec-Labrador Peninsula, which includes portions of the provinces of Quebec and Newfoundland-Labrador in Canada, and is a region with a history of southward ARVV movement waves. We combined two datasets that were collected and genotyped using different protocols, totalling 675 red fox individuals across the whole region and genotyped across 13 microsatellite markers. We found two genetic clusters across the region, reflecting a latitudinal gradient, and characterized by low genetic differentiation. We also observed weak but significant isolation by distance, which seems to be marginally more important for females than for males. These findings suggest a general lack of resistance to movement in red fox populations across the Quebec-Labrador Peninsula, regardless of sex. Implications of these findings include additional support for the hypothesis of long-distance southward ARVV propagation through its red fox reservoir host.

California Serogroup Viruses in a Changing Canadian Arctic: A Review.

The Arctic is warming at four times the global rate, changing the diversity, activity and distribution of vectors and associated pathogens. While the Arctic is not often considered a hotbed of vector-borne diseases, Jamestown Canyon virus (JCV) and Snowshoe Hare virus (SSHV) are mosquito-borne zoonotic viruses of the California serogroup endemic to the Canadian North. The viruses are maintained by transovarial transmission in vectors and circulate among vertebrate hosts, both of which are not well characterized in Arctic regions. While most human infections are subclinical or mild, serious cases occur, and both JCV and SSHV have recently been identified as leading causes of arbovirus-associated neurological diseases in North America. Consequently, both viruses are currently recognised as neglected and emerging viruses of public health concern. This review aims to summarise previous findings in the region regarding the enzootic transmission cycle of both viruses. We identify key gaps and approaches needed to critically evaluate, detect, and model the effects of climate change on these uniquely northern viruses. Based on limited data, we predict that (1) these northern adapted viruses will increase their range northwards, but not lose range at their southern limits, (2) undergo more rapid amplification and amplified transmission in endemic regions for longer vector-biting seasons, (3) take advantage of northward shifts of hosts and vectors, and (4) increase bite rates following an increase in the availability of breeding sites, along with phenological synchrony between the reproduction cycle of theorized reservoirs (such as caribou calving) and mosquito emergence.

Mechanistic movement models to predict geographic range expansions of ticks and tick-borne pathogens: Case studies with Ixodes scapularis and Amblyomma americanum in eastern North America.

The geographic range of the blacklegged tick, Ixodes scapularis, is expanding northward from the United States into southern Canada, and studies suggest that the lone star tick, Amblyomma americanum, will follow suit. These tick species are vectors for many zoonotic pathogens, and their northward range expansion presents a serious threat to public health. Climate change (particularly increasing temperature) has been identified as an important driver permitting northward range expansion of blacklegged ticks, but the impacts of host movement, which is essential to tick dispersal into new climatically suitable regions, have received limited investigation. Here, a mechanistic movement model was applied to landscapes of eastern North America to explore 1) relationships between multiple ecological drivers and the speed of the northward invasion of blacklegged ticks infected with the causative agent of Lyme disease, Borrelia burgdorferi sensu stricto, and 2) its capacity to simulate the northward range expansion of infected blacklegged ticks and uninfected lone star ticks under theoretical scenarios of increasing temperature. Our results suggest that the attraction of migratory birds (long-distance tick dispersal hosts) to resource-rich areas during their spring migration and the mate-finding Allee effect in tick population dynamics are key drivers for the spread of infected blacklegged ticks. The modeled increases in temperature extended the climatically suitable areas of Canada for infected blacklegged ticks and uninfected lone star ticks towards higher latitudes by up to 31% and 1%, respectively, and with an average predicted speed of the range expansion reaching 61 km/year and 23 km/year, respectively. Differences in the projected spatial distribution patterns of these tick species were due to differences in climate envelopes of tick populations, as well as the availability and attractiveness of suitable habitats for migratory birds. Our results indicate that the northward invasion process of lone star ticks is primarily driven by local dispersal of resident terrestrial hosts, whereas that of blacklegged ticks is governed by long-distance migratory bird dispersal. The results also suggest that mechanistic movement models provide a powerful approach for predicting tick-borne disease risk patterns under complex scenarios of climate, socioeconomic and land use/land cover changes.

Comparing Control Intervention Scenarios for Raccoon Rabies in Southern Ontario between 2015 and 2025.

The largest outbreak of raccoon rabies in Canada was first reported in Hamilton, Ontario, in 2015 following a probable translocation event from the United States. We used a spatially-explicit agent-based model to evaluate the effectiveness of provincial control programs in an urban-centric outbreak if control interventions were used until 2025, 2020, or never used. Calibration tests suggested that a seroprevalence of protective rabies antibodies 2.1 times higher than that inferred from seroprevalence in program assessments was required in simulations to replicate observed raccoon rabies cases. Our simulation results showed that if control interventions with an adjusted seroprevalence were used until 2025 or 2020, the probability of rabies elimination due to control intervention use was 49.2% and 42.1%, respectively. However, if controls were never used, the probability that initial rabies cases failed to establish a sustained outbreak was only 18.2%. In simulations where rabies was not successfully eliminated, using control interventions until 2025 resulted in 67% fewer new infections compared to only applying controls until 2020 and in 90% fewer new infections compared to no control intervention use. However, the model likely underestimated rabies elimination rates since we did not adjust for adaptive control strategies in response to changes in rabies distributions and case numbers, as well as extending control interventions past 2025. Our agent-based model offers a cost-effective strategy to evaluate approaches to rabies control applications.

Integrated human behavior and tick risk maps to prioritize Lyme disease interventions using a 'One Health' approach.

Lyme disease (LD) risk is emerging rapidly in Canada due to range expansion of its tick vectors, accelerated by climate change. The risk of contracting LD varies geographically due to variability in ecological characteristics that determine the hazard (the densities of infected host-seeking ticks) and vulnerability of the human population determined by their knowledge and adoption of preventive behaviors. Risk maps are commonly used to support public health decision-making on Lyme disease, but the ability of the human public to adopt preventive behaviors is rarely taken into account in their development, which represents a critical gap. The objective of this work was to improve LD risk mapping using an integrated social-behavioral and ecological approach to: (i) compute enhanced integrated risk maps for prioritization of interventions and (ii) develop a spatially-explicit assessment tool to examine the relative contribution of different risk factors. The study was carried out in the Estrie region located in southern Québec. The blacklegged tick, Ixodes scapularis, infected with the agent of LD is widespread in Estrie and as a result, regional LD incidence is the highest in the province. LD knowledge and behaviors in the population were measured in a cross-sectional health survey conducted in 2018 reaching 10,790 respondents in Estrie. These data were used to create an index for the social-behavioral component of risk in 2018. Local Empirical Bayes estimator technique were used to better quantify the spatial variance in the levels of adoption of LD preventive activities. For the ecological risk analysis, a tick abundance model was developed by integrating data from ongoing long-term tick surveillance programs from 2007 up to 2018. Social-behavioral and ecological components of the risk measures were combined to create vulnerability index maps and, with the addition of human population densities, prioritization index maps. Map predictions were validated by testing the association of high-risk areas with the current spatial distribution of human cases of LD and reported tick exposure. Our results demonstrated that social-behavioral and ecological components of LD risk have markedly different distributions within Estrie. The occurrence of human LD cases or reported tick exposure in a municipality was positively associated with tick density and the prioritization risk index (p < 0.001). This research is a second step towards a more comprehensive integrated LD risk assessment approach, examining social-behavioral risk factors that interact with ecological risk factors to influence the management of emerging tick-borne diseases, an approach that could be applied more widely to vector-borne and zoonotic diseases.

The added value of One Health surveillance: data from questing ticks can provide an early signal for anaplasmosis outbreaks in animals and humans.

OBJECTIVE: In 2021, a first outbreak of anaplasmosis occurred in animals and humans in southern Québec, with 64% of confirmed human cases located in Bromont municipality. Ixodes scapularis ticks and Peromyscus mouse ear biopsies collected in Bromont from 2019 to 2021 were analyzed for Anaplasma phagocytophilum (Ap) with the objective of determining whether an early environmental signal could have been detected before the outbreak. METHODS: Samples were collected for a concurrent study aiming to reduce Lyme disease risk. Between 2019 and 2021, up to 14 experimental sites were sampled for ticks and capture of small mammals took place on three sites in 2021. Samples were screened for Ap using multiplex real-time PCR, and genetic strains were identified using a single-nucleotide polymorphism assay. RESULTS: Analyses showed an increase of 5.7% in Ap prevalence in ticks (CI95: 1.5-9.9) between 2019 and 2020, i.e., one year before the outbreak. A majority of Ap-positive ticks were infected with the zoonotic strain (68.8%; CI95: 50.0-83.9) during the study period. In 2021, 2 of 59 captured Peromycus mice were positive for Ap, for a prevalence of 3.4% (CI95: 0.4-11.7). CONCLUSION: We conclude that data collected in Bromont could have provided an early signal for an anaplasmosis risk increasing in the targeted region. This is a reminder that integrated surveillance of tick-borne diseases through structured One Health programs, i.e. systematically integrating data from humans, animals and the environment, can provide useful and timely information for better preparedness and response in public health.

RéSUMé: OBJECTIF: En 2021, suivant une éclosion d'anaplasmoses chez les animaux et les humains dans le sud du Québec, des tiques de l'espèce Ixodes scapularis et des biopsies de souris Peromyscus spp. échantillonées à Bromont, la municipalité où 64 % des cas humains confirmés était localisé, ont été testées pour Anaplasma phagocytophilum (Ap) avec pour objectif de déterminer si un signal environnemental précoce d'augmentation du risque aurait pu être détecté avant l'éclosion. MéTHODE: L'échantillonnage a été réalisé dans le cadre d'une étude visant à réduire le risque de maladie de Lyme. De 2019 à 2021, 14 sites expérimentaux ont été échantillonnés pour les tiques. En 2021, trois sites ont été sélectionnés pour la capture des micromammifères. Les échantillons ont été testés pour la présence d'Ap à l'aide d'un PCR multiplex en temps réelle et les lignées génétiques ont été identifiées grâce à un test de polymorphisme mononucléotidique. RéSULTATS: Les analyses ont montré une augmentation de 5,7 % (IC95% : 1,5­9,9) de la prévalence de Ap entre 2019 et 2020, c'est-à-dire un an avant l'éclosion. Cette augmentation est associée à la présence d'une majorité d'Ap de la lignée zoonotique (68,8 %; IC95% : 50,0­83,9) sur l'ensemble de la période étudiée. En 2021, deux Peromycus spp. capturées sur 59 étaient positives pour Ap pour une prévalence de 3,4 % (IC95% : 0,4­11,7). CONCLUSION: Les données environnementales échantillonnées à Bromont auraient pu fournir un signal précoce de l'augmentation du risque d'anaplasmose dans la région. C'est un rappel que la surveillance intégrée des maladies transmises par les tiques inspirée de l'approche Une seule santé, intégrant systématiquement des données humaines, animales et environnementales, peut fournir des informations utiles et opportunes aux autorités de santé publique.

Criteria for selecting sentinel unit locations in a surveillance system for vector-borne disease: A decision tool.

Objectives: With vector-borne diseases emerging across the globe, precipitated by climate change and other anthropogenic changes, it is critical for public health authorities to have well-designed surveillance strategies in place. Sentinel surveillance has been proposed as a cost-effective approach to surveillance in this context. However, spatial design of sentinel surveillance system has important impacts on surveillance outcomes, and careful selection of sentinel unit locations is therefore an essential component of planning. Methods: A review of the available literature, based on the realist approach, was used to identify key decision issues for sentinel surveillance planning. Outcomes of the review were used to develop a decision tool, which was subsequently validated by experts in the field. Results: The resulting decision tool provides a list of criteria which can be used to select sentinel unit locations. We illustrate its application using the case example of designing a national sentinel surveillance system for Lyme disease in Canada. Conclusions: The decision tool provides researchers and public health authorities with a systematic, evidence-based approach for planning the spatial design of sentinel surveillance systems, taking into account the aims of the surveillance system and disease and/or context-specific considerations.

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

The development of interventions that reduce Lyme disease incidence remains a challenge. Reservoir-targeted approaches aiming to reduce tick densities or tick infection prevalence with Borrelia burgdorferi have emerged as promising ways to reduce the density of infected ticks. Acaricides of the isoxazoline family offer high potential for reducing infestation of ticks on small mammals as they have high efficacy at killing feeding ticks for a long period. Fluralaner baits were recently demonstrated as effective, in the laboratory, at killing Ixodes scapularis larvae infesting Peromyscus mice, the main reservoir for B. burgdorferi in northeastern North America. Here, effectiveness of this approach for reducing the infestation of small mammals by immature stages of I. scapularis was tested in a natural environment. Two densities of fluralaner baits (2.1 baits/1,000 m2 and 4.4 baits/1,000 m2) were used during three years in forest plots. The number of I. scapularis larvae and nymphs per mouse from treated and control plots were compared. Fluralaner baiting reduced the number of larvae per mouse by 68% (CI95: 51-79%) at 2.1 baits/1,000 m2 and by 86% (CI95: 77-92%) at 4.4 baits/1,000 m2. The number of nymphs per mouse was reduced by 72% (CI95: 22-90%) at 4.4 baits/1,000 m2 but was not significantly reduced at 2.1 baits/1,000 m2. Reduction of Peromyscus mouse infestation by immature stages of I. scapularis supports the hypothesis that an approach targeting reservoirs of B. burgdorferi with isoxazolines has the potential to reduce tick-borne disease risk by decreasing the density of infected ticks in the environment.

Sentinel Surveillance Contributes to Tracking Lyme Disease Spatiotemporal Risk Trends in Southern Quebec, Canada.

Lyme disease (LD) is a tick-borne disease which has been emerging in temperate areas in North America, Europe, and Asia. In Quebec, Canada, the number of human LD cases is increasing rapidly and thus surveillance of LD risk is a public health priority. In this study, we aimed to evaluate the ability of active sentinel surveillance to track spatiotemporal trends in LD risk. Using drag flannel data from 2015-2019, we calculated density of nymphal ticks (DON), an index of enzootic hazard, across the study region (southern Quebec). A Poisson regression model was used to explore the association between the enzootic hazard and LD risk (annual number of human cases) at the municipal level. Predictions from models were able to track both spatial and interannual variation in risk. Furthermore, a risk map produced by using model predictions closely matched the official risk map published by provincial public health authorities, which requires the use of complex criteria-based risk assessment. Our study shows that active sentinel surveillance in Quebec provides a sustainable system to follow spatiotemporal trends in LD risk. Such a network can support public health authorities in informing the public about LD risk within their region or municipality and this method could be extended to support Lyme disease risk assessment at the national level in Canada.

The utility of a maximum entropy species distribution model for Ixodes scapularis in predicting the public health risk of Lyme disease in Ontario, Canada.

Lyme disease is an emerging public health threat in Ontario, Canada due to ongoing range expansion of the tick vector, Ixodes scapularis. Tick density is an important predictor of human Lyme disease risk and is typically measured using active tick surveillance via drag sampling, which is time and resource-intensive. New cost-effective tools are needed to augment current surveillance activities. Our objective was to evaluate the ability of a maximum entropy (Maxent) species distribution model to predict I. scapularis density in three regions of Ontario - Ottawa, Kingston, and southern Ontario - in order to determine its utility in predicting the public health risk of Lyme disease. Ticks were collected via drag sampling at 60 sites across the three regions. Model-predicted habitat suitability was calculated from a previously constructed Maxent model as the mean predicted habitat suitability within a 1-km radius of each site. Spearman's correlation coefficient was used to quantify the continuous relationship between model-predicted habitat suitability and tick density, and negative binomial regression was used to quantify the relationship between tick density and model-predicated habitat suitability. Spearman's correlation coefficients for the full study area, Kingston region, and Ottawa region were 0.517, 0.707, and 0.537, respectively, indicating a moderate positive relationship and ability of the model to predict tick density. Regression analysis further demonstrated a significant positive association between tick density and model-predicted habitat suitability (p< 0.001). Using a dichotomized measure of model-predicted habitat suitability, the incidence rate ratio - the ratio of ticks per m2 in sites predicted to have a 'suitable' habitat compared to those predicted to have 'not suitable' habitat - was 33.95, indicating that tick density was significantly higher at sites situated in areas with predicted suitable habitat. Given that tick density is an important component of Lyme disease risk, the ability to predict high tick density locations using the Maxent model may make it a cost-effective tool for identifying geographic areas that pose elevated public health risk of Lyme disease.

Context-dependent host dispersal and habitat fragmentation determine heterogeneity in infected tick burdens: an agent-based modelling study.

As the incidence of tick-borne diseases has sharply increased over the past decade, with serious consequences for human and animal health, there is a need to identify ecological drivers contributing to heterogeneity in tick-borne disease risk. In particular, the relative importance of animal host dispersal behaviour in its three context-dependent phases of emigration, transfer and settlement is relatively unexplored. We built a spatially explicit agent-based model to investigate how the host dispersal process, in concert with the tick and host demographic processes, habitat fragmentation and the pathogen transmission process, affects infected tick distributions among hosts. A sensitivity analysis explored the impacts of different input parameters on infected tick burdens on hosts and infected tick distributions among hosts. Our simulations indicate that ecological predictors of infected tick burdens differed among the post-egg life stages of ticks, with tick attachment and detachment, tick questing activity and pathogen transmission dynamics identified as key processes, in a coherent way. We also found that the type of host settlement strategy and the proportion of habitat suitable for hosts determined super-spreading of infected ticks. We developed a theoretical mechanistic framework that can serve as a first step towards applied studies of on-the-ground public health intervention strategies.

Transmission patterns of tick-borne pathogens among birds and rodents in a forested park in southeastern Canada.

Ixodes scapularis ticks are expanding their range in parts of northeastern North America, bringing with them pathogens of public health concern. While rodents like the white-footed mouse, Peromyscus leucopus, are considered the primary reservoir of many emerging tick-borne pathogens, the contribution of birds, as alternative hosts and reservoirs, to local transmission cycles has not yet been firmly established. From 2016 to 2018, we collected host-seeking ticks and examined rodent and bird hosts for ticks at 48 sites in a park where blacklegged ticks are established in Quebec, Canada, in order to characterize the distribution of pathogens in ticks and mammalian and avian hosts. We found nearly one third of captured birds (n = 849) and 70% of small mammals (n = 694) were infested with I. scapularis. Five bird and three mammal species transmitted Borrelia burgdorferi to feeding larvae (n larvae tested = 2257) and we estimated that about one fifth of the B. burgdorferi-infected questing nymphs in the park acquired their infection from birds, the remaining being attributable to mice. Ground-foraging bird species were more parasitized than other birds, and species that inhabited open habitat were more frequently infested and were more likely to transmit B. burgdorferi to larval ticks feeding upon them. Female birds were more likely to transmit infection than males, without age differentiation, whereas in mice, adult males were more likely to transmit infection than juveniles and females. We also detected Borrelia miyamotoi in larvae collected from birds, and Anaplasma phagocytophilum from a larva collected from a white-footed mouse. This study highlights the importance of characterising the reservoir potential of alternative reservoir hosts and to quantify their contribution to transmission dynamics in different species assemblages. This information is key to identifying the most effective host-targeted risk mitigation actions.

Effects of land use and weather on the presence and abundance of mosquito-borne disease vectors in a urban and agricultural landscape in Eastern Ontario, Canada.

Weather and land use can significantly impact mosquito abundance and presence, and by consequence, mosquito-borne disease (MBD) dynamics. Knowledge of vector ecology and mosquito species response to these drivers will help us better predict risk from MBD. In this study, we evaluated and compared the independent and combined effects of weather and land use on mosquito species occurrence and abundance in Eastern Ontario, Canada. Data on occurrence and abundance (245,591 individuals) of 30 mosquito species were obtained from mosquito capture at 85 field sites in 2017 and 2018. Environmental variables were extracted from weather and land use datasets in a 1-km buffer around trapping sites. The relative importance of weather and land use on mosquito abundance (for common species) or occurrence (for all species) was evaluated using multivariate hierarchical statistical models. Models incorporating both weather and land use performed better than models that include weather only for approximately half of species (59% for occurrence model and 50% for abundance model). Mosquito occurrence was mainly associated with temperature whereas abundance was associated with precipitation and temperature combined. Land use was more often associated with abundance than occurrence. For most species, occurrence and abundance were positively associated with forest cover but for some there was a negative association. Occurrence and abundance of some species (47% for occurrence model and 88% for abundance model) were positively associated with wetlands, but negatively associated with urban (Culiseta melanura and Anopheles walkeri) and agriculture (An. quadrimaculatus, Cs. minnesotae and An. walkeri) environments. This study provides predictive relationships between weather, land use and mosquito occurrence and abundance for a wide range of species including those that are currently uncommon, yet known as arboviruses vectors. Elucidation of these relationships has the potential to contribute to better prediction of MBD risk, and thus more efficiently targeted prevention and control measures.

Surveillance for Ixodes scapularis and Ixodes pacificus ticks and their associated pathogens in Canada, 2019.

Background: The primary vectors of the agent of Lyme disease in Canada are Ixodes scapularis and Ixodes pacificus ticks. Surveillance for ticks and the pathogens they can transmit can inform local tick-borne disease risk and guide public health interventions. The objective of this article is to characterize passive and active surveillance of the main Lyme disease tick vectors in Canada in 2019 and the tick-borne pathogens they carry. Methods: Passive surveillance data were compiled from the National Microbiology Laboratory Branch and provincial public health data sources. Active surveillance was conducted in selected sentinel sites in all provinces. Descriptive analysis of ticks submitted and infection prevalence of tick-borne pathogens are presented. Seasonal and spatial trends are also described. Results: In passive surveillance, specimens of I. scapularis (n=9,858) were submitted from all provinces except British Columbia and I. pacificus (n=691) were submitted in British Columbia and Alberta. No ticks were submitted from the territories. The seasonal distribution pattern was bimodal for I. scapularis adults, but unimodal for I. pacificus adults. Borrelia burgdorferi was the most prevalent pathogen in I. scapularis (18.8%) and I. pacificus (0.3%). In active surveillance, B. burgdorferi was identified in 26.2% of I. scapularis; Anaplasma phagocytophilum in 3.4% of I. scapularis, and Borrelia miyamotoi and Powassan virus in 0.5% or fewer of I. scapularis. These same tick-borne pathogens were not found in the small number of I. pacificus tested. Conclusion: This surveillance article provides a snapshot of the main Lyme disease vectors in Canada and their associated pathogens, which can be used to monitor emerging risk areas for exposure to tick-borne pathogens.

Fine-scale determinants of the spatiotemporal distribution of Ixodes scapularis in Quebec (Canada).

The tick vector of Lyme disease, Ixodes scapularis, is currently expanding its geographical distribution northward into southern Canada driving emergence of Lyme disease in the region. Despite large-scale studies that attributed different factors such as climate change and changes in land use to the geographical expansion of the tick, a comprehensive understanding of local patterns of tick abundance is still lacking in that region. Using a newly endemic periurban nature park located in Quebec (Canada) as a model, we explored intra-habitat patterns in tick distribution and their relationship with biotic and abiotic factors. We verified the hypotheses that (1) there is spatial heterogeneity in tick densities at the scale of the park and (2) these patterns can be explained by host availability, habitat characteristics and microclimatic conditions. During tick activity season in three consecutive years, tick, deer, rodent and bird abundance, as well as habitat characteristics and microclimatic conditions, were estimated at thirty-two sites. Patterns of tick distribution and abundance were investigated by spatial analysis. Generalised additive mixed models were constructed for each developmental stage of the tick and the relative importance of significant drivers on tick abundance were derived from final models. We found fine-scale spatial heterogeneity in densities of all tick stages across the park, with interannual variability in the location of hotspots. For all stages, the local density was related to the density of the previous stage in the previous season, in keeping with the tick's life cycle. Adult tick density was highest where drainage was moderate (neither waterlogged nor dry). Microclimatic conditions influenced the densities of immature ticks, through the effects of weather at the time of tick sampling (ambient temperature and relative humidity) and of the seasonal microclimate at the site level (degree-days and number of tick adverse moisture events). Seasonal phenology patterns were generally consistent with expected curves for the region, with exceptions in some years that may be attributable to founder events. This study highlights fine scale patterns of tick population dynamics thus providing fundamental knowledge in Lyme disease ecology and information applicable to the development of well-targeted prevention and control strategies for public natural areas affected by this growing problem in southern Canada.