Reconciling the Entomological Hazard and Disease Risk in the Lyme Disease System

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.

Assessing the Influence of Climate Change and Environmental Factors on the Top Tick-Borne Diseases in the United States: A Systematic Review

In the United States (US), tick-borne diseases (TBDs) have more than doubled in the past fifteen years and are a major contributor to the overall burden of vector-borne diseases. The most common TBDs in the US-Lyme disease, rickettsioses (including Rocky Mountain spotted fever), and anaplasmosis-have gradually shifted in recent years, resulting in increased morbidity and mortality. In this systematic review, we examined climate change and other environmental factors that have influenced the epidemiology of these TBDs in the US while highlighting the opportunities for a One Health approach to mitigating their impact. We searched Medline Plus, PUBMED, and Google Scholar for studies focused on these three TBDs in the US from January 2018 to August 2023. Data selection and extraction were completed using Covidence, and the risk of bias was assessed with the ROBINS-I tool. The review included 84 papers covering multiple states across the US. We found that climate, seasonality and temporality, and land use are important environmental factors that impact the epidemiology and patterns of TBDs. The emerging trends, influenced by environmental factors, emphasize the need for region-specific research to aid in the prediction and prevention of TBDs.

Collaborative Modeling of the Tick-Borne Disease Social-Ecological System: A Conceptual Framework

Hard-bodied ticks have become a major concern in temperate regions because they transmit a variety of pathogens of medical significance. Ticks and pathogens interact with hosts in a complex social-ecological system (SES) that influences human exposure to tick-borne diseases (TBD). We argue that addressing the urgent public health threat posed by TBD requires an understanding of the integrated processes in the forest ecosystem that influence tick density and infection prevalence, transmission among ticks, animal hosts, and ultimately disease prevalence in humans. We argue that collaborative modeling of the human-tick SES is required to understand the system dynamics as well as move science toward policy action. Recent studies in human health have shown the importance of stakeholder participation in understanding the factors that contribute to human exposure to zoonotic diseases. We discuss how collaborative modeling can be applied to understand the impacts of forest management practices on ticks and TBD. We discuss the potential of collaborative modeling for encouraging participation of diverse stakeholders in discussing the implications of managing forest ticks in the absence of large-scale control policy.

Perceived vulnerability for Lyme disease questionnaire: A social science tool for understanding tick-borne disease attitudes

Lyme disease has emerged as a growing epidemic across the U.S., with tick populations spreading north because of a plethora of human-induced factors. As the scope of this problem grows, there is a need to understand how vulnerable the public perceives themselves to be and how perceived vulnerability as a psychological construct influences public behavior. A growing body of literature has explored individual risk perceptions and individual preventative behaviors toward Lyme disease, but there remains a notable research gap regarding the concept of vulnerability. This empirical study establishes the first questionnaire for perceived vulnerability towards Lyme disease, modified from pre-existing infectious disease literature. This novel instrument was tested and compared with individual factors relating to preventative behaviors and source credibility of major information sources about Lyme disease in the state of Maine. Recent increases in black-legged tick (Ixodes scapularis) populations have affected the state of Maine in dramatic ways. This research specifically surveyed homeowners to explore their perceived vulnerability, source credibility, and individual protective intentions related to ticks and Lyme disease in Maine. Results from this study validate a modified perceived vulnerability scale for Lyme disease and highlight how understanding the relationships between these perceptions of vulnerability, individual behaviors, and sources of information can improve outreach and communication efforts about tick-borne diseases.

An ecological approach to predict areas with established populations of Ixodes scapularis in Quebec, Canada

Public health management of Lyme disease (LD) is a dynamic challenge in Canada. Climate warming is driving the northward expansion of suitable habitat for the tick vector, Ixodes scapularis. Information about tick population establishment is used to inform the risk of LD but is challenged by sampling biases from surveillance data. Misclassifying areas as having no established tick population underestimates the LD risk classification. We used a logistic regression model at the municipal level to predict the probability of I. scapularis population establishment based on passive tick surveillance data during the period of 2010-2017 in southern Quebec. We tested for the effect of abiotic and biotic factors hypothesized to influence tick biology and ecology. Additional variables controlled for sampling biases in the passive surveillance data. In our final selected model, tick population establishment was positively associated with annual cumulative degree-days > 0°C, precipitation and deer density, and negatively associated with coniferous and mixed forest types. Sampling biases from passive tick surveillance were controlled for using municipal population size and public health instructions on tick submissions. The model performed well as indicated by an area under the curve (AUC) of 0.92, sensitivity of 86% and specificity of 81%. Our model enables prediction of I. scapularis population establishment in areas which lack data from passive tick surveillance and may improve the sensitivity of LD risk categorization in these areas. A more sensitive system of LD risk classification is important for increasing awareness and use of protective measures employed against ticks, and decreasing the morbidity associated with LD.

Risk of tick-borne pathogen spillover into urban yards in New York City

BACKGROUND

The incidence of tick-borne disease has increased dramatically in recent decades, with urban areas increasingly recognized as high-risk environments for exposure to infected ticks. Green spaces may play a key role in facilitating the invasion of ticks, hosts and pathogens into residential areas, particularly where they connect residential yards with larger natural areas (e.g. parks). However, the factors mediating tick distribution across heterogeneous urban landscapes remain poorly characterized.

METHODS

Using generalized linear models in a multimodel inference framework, we determined the residential yard- and local landscape-level features associated with the presence of three tick species of current and growing public health importance in residential yards across Staten Island, a borough of New York City, in the state of New York, USA.

RESULTS

The amount and configuration of canopy cover immediately surrounding residential yards was found to strongly predict the presence of Ixodes scapularis and Amblyomma americanum, but not that of Haemaphysalis longicornis. Within yards, we found a protective effect of fencing against I. scapularis and A. americanum, but not against H. longicornis. For all species, the presence of log and brush piles strongly increased the odds of finding ticks in yards.

CONCLUSIONS

The results highlight a considerable risk of tick exposure in residential yards in Staten Island and identify both yard- and landscape-level features associated with their distribution. In particular, the significance of log and brush piles for all three species supports recommendations for yard management as a means of reducing contact with ticks.

Relevance of Spatial and Temporal Trends in Nymphal Tick Density and Infection Prevalence for Public Health and Surveillance Practice in Long-Term Endemic Areas: A Case Study in Monmouth County, NJ

Tick-borne diseases are a growing public health problem in the United States, and the US northeast has reported consistently high case rates for decades. Monmouth County, New Jersey, was one of the earliest jurisdictions to report Lyme disease cases in 1979 and reports several hundred cases per year nearly 40 yr later. In the time since, however, tick-borne health risks have expanded far beyond Lyme disease to include a variety of other bacterial pathogens and viruses, and additional vectors, necessitating a continually evolving approach to tick surveillance. In 2017, Monmouth County initiated an active surveillance program targeting sites across three ecological regions for collection of Ixodes scapularis Say (Acari: Ixodidae) and Amblyomma americanum L. (Acari: Ixodidae) as well as testing via qPCR for associated bacterial pathogens. During the first five years of this program (2017-2021), we report high levels of spatiotemporal variability in nymphal density and infection prevalence in both species, limiting the granularity with which human risk can be predicted from acarological data. Nonetheless, broader patterns emerged, including an ongoing trend of A. americanum dominance, risks posed by Borrelia miyamotoi, and the frequency of coinfected ticks. We present some of the first county-level, systematic surveillance of nymphal A. americanum density and infection prevalence in the northeastern US. We also documented a temporary decline in Borrelia burgdorferi that could relate to unmeasured trends in reservoir host populations. We discuss the implications of our findings for tick-borne disease ecology, public health communication, and tick surveillance strategies in endemic areas.

A Geographic Information System Approach to Map Tick Exposure Risk at a Scale for Public Health Intervention

Tick-borne disease control and prevention have been largely ineffective compared to the control of other vector-borne diseases. Although control strategies exist, they are costly or ineffective at large spatial scales. We need tools to target these strategies to places of highest tick exposure risk. Here we present a geographic information system (GIS) method for mapping predicted tick exposure risk at a 200 m by 200 m resolution, appropriate for public health intervention. We followed the approach used to map tick habitat suitability over large areas. We used drag-cloth sampling to measure the density of nymphal blacklegged ticks (Ixodes scapularis, Say (Acari: Ixodidae)) at 24 sites in Addison and Rutland Counties, VT, United States. We used a GIS to average habitat, climatological, land-use/land-cover, and abiotic characteristics over 100 m, 400 m, 1,000 m, and 2,000 m buffers around each site to evaluate which characteristic at which buffer size best predicted density of nymphal ticks (DON). The relationships between predictor variables and DON were determined with random forest models. The 100 m buffer model performed best and explained 37.7% of the variation in DON, although was highly accurate at classifying sites as having below or above average DON. This model was applied to Addison County, VT, to predict tick exposure risk at a 200 m resolution. This GIS approach to map predicted DON over a small area with fine resolution, could be used to target public health campaigns and land management practices to reduce human exposure to ticks.

Host contributions to the force of Borrelia burgdorferi and Babesia microti transmission differ at edges of and within a small habitat patch

In the northeastern United States, the emergence of Lyme disease has been associated, in part, with the increase of small forest patches. Such disturbed habitat is exploited by generalist species, such as white-footed mice, which are considered the host with the greatest reservoir capacity for the agents of Lyme disease (Borrelia burgdorferi sensu stricto) and human babesiosis (Babesia microti). Spatial risk analyses have identified edge habitat as particularly risky. Using a retrotransposon-based quantitative PCR assay for host bloodmeal remnant identification, we directly measured whether the hosts upon which vector ticks fed differed at the edge or within the contiguous small habitat patch. Questing nymphal deer ticks, Ixodes dammini, the northern clade of Ixodes scapularis, were collected from either the edge or within a thicket on Nantucket Island over 3 transmission seasons and tested for evidence of infection as well as bloodmeal hosts. Tick bloodmeal hosts significantly differed by site as well as by year. Mice and deer were identified most often (49.9%), but shrews, rabbits and birds were also common. Ticks from the edge fed on a greater diversity of hosts than those from the thicket. Surprisingly, mice were not strongly associated with either infection at either sampling site (OR<2 for all). Although shrews were not the most common host utilized by ticks, they were highly associated with both infections at both sites (OR= 4.5 and 7.9 B. burgdorferi and 7.9 and 19.0 B. microti, edge and thicket). We conclude that reservoir hosts may differ in their contributions to infecting ticks between edge and contiguous vegetated patches. Importance Habitat fragmentation is thought to be a main factor in the emergence of Lyme disease and other of the deer tick-transmitted infections. The patchwork of forest and edges promotes altered biodiversity, favoring the abundance of generalist rodents such as white footed mice, heretofore considered a key tick and reservoir host in the northeastern U.S. We used tick bloodmeal analyses to directly identify the hosts from which nymphal deer ticks became infected. We demonstrate that there is considerable microfocality in host contributions to the cohort of infected ticks and that shrews, although they fed fewer ticks than mice, disproportionately influenced the force of pathogen transmission in our site. The venue of transmission of certain deer tick-transmitted agents may comprise a habitat scale of 10 meters or fewer and depend on alternative small mammal hosts such as shrews.

Exposure, hazard, and vulnerability all contribute to Schistosoma haematobium re-infection in northern Senegal

Background

Infectious disease risk is driven by three interrelated components: exposure, hazard, and vulnerability. For schistosomiasis, exposure occurs through contact with water, which is often tied to daily activities. Water contact, however, does not imply risk unless the environmental hazard of snails and parasites is also present in the water. By increasing reliance on hazardous activities and environments, socio-economic vulnerability can hinder reductions in exposure to a hazard. We aimed to quantify the contributions of exposure, hazard, and vulnerability to the presence and intensity of Schistosoma haematobium re-infection.

Methodology/Principal findings

In 13 villages along the Senegal River, we collected parasitological data from 821 school-aged children, survey data from 411 households where those children resided, and ecological data from all 24 village water access sites. We fit mixed-effects logistic and negative binomial regressions with indices of exposure, hazard, and vulnerability as explanatory variables of Schistosoma haematobium presence and intensity, respectively, controlling for demographic variables. Using multi-model inference to calculate the relative importance of each component of risk, we found that hazard (Ʃw_{i =} 0.95) was the most important component of S. haematobium presence, followed by vulnerability (Ʃw_i = 0.91). Exposure (Ʃw_i = 1.00) was the most important component of S. haematobium intensity, followed by hazard (Ʃw_i = 0.77). Model averaging quantified associations between each infection outcome and indices of exposure, hazard, and vulnerability, revealing a positive association between hazard and infection presence (OR = 1.49, 95% CI 1.12, 1.97), and a positive association between exposure and infection intensity (RR 2.59–3.86, depending on the category; all 95% CIs above 1)

Conclusions/Significance

Our findings underscore the linkages between social (exposure and vulnerability) and environmental (hazard) processes in the acquisition and accumulation of S. haematobium infection. This approach highlights the importance of implementing both social and environmental interventions to complement mass drug administration.

While the impacts of natural hazards tend to be described in terms of social determinants such as exposure and vulnerability, the risk for infectious disease is often expressed in terms of environmental determinants without fully considering the socio-ecological processes that put people in contact with infective agents of disease. In the case of schistosomiasis, risk is determined by human interactions with freshwater environments where schistosome parasites circulate between people and aquatic snails. In this study, we quantified the relative contributions of exposure, hazard, and vulnerability to schistosome re-infection among schoolchildren in an endemic region of northern Senegal. We find that hazard and vulnerability influence whether a child becomes infected, while exposure and hazard influence the burden of worms once infection is acquired. Increasing numbers of worms is known to be positively associated with increasing severity of disease. Our findings underscore the importance of evaluating social and environmental determinants of disease simultaneously; omitting measures of exposure, hazard or vulnerability may limit our understanding of risk.

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.

Environmental Correlates of Lyme Disease Emergence in Southwest Virginia, 2005-2014

Lyme disease is the most common tick-borne disease in North America. Though human infection is mostly transmitted in a limited geography, the range has expanded in recent years. One notable area of recent expansion is in the mountainous region of southwestern Virginia. The ecological factors that facilitate or constrain the range of human Lyme disease in this region remain uncertain. To evaluate this further, we obtained ecological data, including remotely sensed data on forest structure and vegetation, weather data, and elevation. These data were aggregated within the census block groups of a 9,153 km2 area around the cities of Blacksburg and Roanoke, VA, an area with heterogeneous Lyme disease transmission. In this geographic area, 755 individuals were reported to have Lyme disease in the 10 yr from 2006 to 2015, and these cases were aggregated by block group. A zero-inflated negative binomial model was used to evaluate which environmental variables influenced the abundance of Lyme disease cases. Higher elevation and higher vegetation density had the greatest effect size on the abundance of Lyme disease. Measures of forest edge, forest integrity, temperature, and humidity were not associated with Lyme disease cases. Future southward expansion of Lyme disease into the southeastern states may be most likely in ecologically similar mountainous areas.

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.

Current and Future Spatiotemporal Patterns of Lyme Disease Reporting in the Northeastern United States

IMPORTANCE

The incidence and geographic range of Lyme disease continues to increase in the United States because of the expansion of Ixodes scapularis, the species of tick that is the main Lyme disease vector. Currently, no dynamic model for the disease spread exists that integrates information of both acarological and human case surveillance data.

OBJECTIVE

To characterize the spatiotemporal spread of Lyme disease in humans among counties in US endemic regions.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study modeled the spread of Lyme disease county-level case reporting, accounting for county-level demographic factors, environmental factors associated with tick presence and human exposure, and the spatiotemporal association between counties. The analyses were conducted between January and August 2019. The setting was 1405 counties in the following regions of the United States: West North Central, East North Central, New England, Middle Atlantic, and the South. Assessments were based on publicly available Lyme disease case data reported to the US Centers for Disease Control and Prevention (CDC) between January 2000 and December 2017.

MAIN OUTCOMES AND MEASURES

Probability of reporting the first case of Lyme disease by county by year.

RESULTS

Between 2000 and 2017, a total of 497 569 Lyme disease cases were reported to the CDC in the study area. Reporting a first case of Lyme disease was associated with a county's and county's neighbors' forest coverage, elevation, percentage of population living in the wildland-urban interface, tick presence, county's population size, proportion of neighbors reporting cases, and neighbors' years since first reporting. The model that included these variables showed high predictive power, with a mean area under the receiver operating characteristic curve of 81.1 (95% CI, 68.5-86.2). The model predicted the first reported Lyme disease case a mean (SD) of 5.5 (3.5) years earlier than was reported to the CDC, with a mean spread velocity estimated at 27.4 (95% CI, 13.6-54.4) km per year. Among 162 counties without reported cases, 47 (29.0%) had a high probability of reporting Lyme disease by 2018. The estimated mean time lag between the first reported case in a neighboring county and any county was 7 (95% CI, 3-8) years.

CONCLUSIONS AND RELEVANCE

This study's findings suggest that, if updated regularly and expanded geographically, this predictive model could enable states and counties to develop more specific Lyme disease prevention and control plans, including improved sensitization of the general population and medical community.

Comparing the Climatic and Landscape Risk Factors for Lyme Disease Cases in the Upper Midwest and Northeast United States

Lyme disease, recognized as one of the most important vector-borne diseases worldwide, has been increasing in incidence and spatial extend in United States. In the Northeast and Upper Midwest, Lyme disease is transmitted by Ixodes scapularis. Currently, many studies have been conducted to identify factors influencing Lyme disease risk in the Northeast, however, relatively few studies focused on the Upper Midwest. In this study, we explored and compared the climatic and landscape factors that shape the spatial patterns of human Lyme cases in these two regions, using the generalized linear mixed models. Our results showed that climatic variables generally had opposite correlations with Lyme disease risk, while landscape factors usually had similar effects in these two regions. High precipitation and low temperature were correlated with high Lyme disease risk in the Upper Midwest, while with low Lyme disease risk in the Northeast. In both regions, size and fragmentation related factors of residential area showed positive correlations with Lyme disease risk. Deciduous forests and evergreen forests had opposite effects on Lyme disease risk, but the effects were consistent between two regions. In general, this study provides new insight into understanding the differences of risk factors of human Lyme disease risk in these two regions.

Enhancement of Risk for Lyme Disease by Landscape Connectivity, New York, New York, USA

Most tickborne disease studies in the United States are conducted in low-intensity residential development and forested areas, leaving much unknown about urban infection risks. To understand Lyme disease risk in New York, New York, USA, we conducted tick surveys in 24 parks throughout all 5 boroughs and assessed how park connectivity and landscape composition contribute to Ixodes scapularis tick nymphal densities and Borrelia burgdorferi infection. We used circuit theory models to determine how parks differentially maintain landscape connectivity for white-tailed deer, the reproductive host for I. scapularis ticks. We found forested parks with vegetated buffers and increased connectivity had higher nymph densities, and the degree of park connectivity strongly determined B. burgdorferi nymphal infection prevalence. Our study challenges the perspective that tickborne disease risk is restricted to suburban and natural settings and emphasizes the need to understand how green space design affects vector and host communities in areas of emerging urban tickborne disease.

Landscape determinants of density of blacklegged ticks, vectors of Lyme disease, at the northern edge of their distribution in Canada

In eastern North America, including Canada, Lyme disease is caused by Borrelia burgdorferi sensu stricto and transmitted to humans by the blacklegged tick, Ixodes scapularis. The last decade has seen a growing incidence of Lyme disease in Canada, following the northward range expansion of I. scapularis tick populations from endemic areas in eastern United States. This may be attributable to movement of the many hosts that they parasitize, including songbirds, deer and small mammals. In this study, we wanted to test the effect of spatial, temporal and ecological variables, on blacklegged tick density and infection rates, near the northern limit of their distribution in Ontario and Quebec, Canada. We found an effect of both proportion of forested areas and distance to roads, on density of I. scapularis ticks and prevalence of infection by B. burgdorferi. We also found an effect of both sampling year and ordinal sampling data on prevalence of infection by B. burgdorferi. In six adjacent sites showing evidence of reproducing I. scapularis populations, we found that forest composition and structure influenced density of I. scapularis ticks. Our results suggest that blacklegged tick density and infection rate in Canada may be influenced by a variety of factors.

Citizen science informs human-tick exposure in the Northeastern United States

BACKGROUND

Tick-borne disease is the result of spillover of pathogens into the human population. Traditionally, literature has focused on characterization of tick-borne disease pathogens and ticks in their sylvatic cycles. A limited amount of research has focused on human-tick exposure in this system, especially in the Northeastern United States. Human-tick interactions are crucial to consider when assessing the risk of tick-borne disease since a tick bite is required for spillover to occur.

METHODS

Citizen scientists collected ticks from the Northeastern US through a free nationwide program. Submitted ticks were identified to species, stage, and sex. Blacklegged ticks, Ixodes scapularis, were tested for the presence of Borrelia burgdorferi sensu lato (s.l.) and hard-tick relapsing fever Borrelia. Seasonality of exposure and the citizen science activity during tick exposure was recorded by the citizen scientist. A negative binomial model was fit to predict county level CDC Lyme disease cases in 2016 using citizen science Ixodes scapularis submissions, state, and county population as predictor variables.

RESULTS

A total of 3740 submissions, comprising 4261 ticks, were submitted from the Northeastern US and were reported to be parasitizing humans. Of the three species submitted, blacklegged ticks were the most prevalent followed by American dog ticks and lone star ticks. Submissions peaked in May with the majority of exposure occurring during every-day activities. The most common pathogen in blacklegged ticks was B. burgdorferi s.l. followed by hard-tick relapsing fever Borrelia. Negative binomial model performance was best in New England states followed by Middle Atlantic states.

CONCLUSIONS

Citizen science provides a low-cost and effective methodology for describing the seasonality and characteristics of human-tick exposure. In the Northeastern US, everyday activities were identified as a major mechanism for tick exposure, supporting the role of peri-domestic exposure in tick-borne disease. Citizen science provides a method for broad pathogen and tick surveillance, which is highly related to human disease, allowing for inferences to be made about the epidemiology of tick-borne disease.

Risk Factors of Lyme Disease: An Intersection of Environmental Ecology and Systems Science

Lyme disease (LD) cases have been on the rise throughout the United States, costing the healthcare system up to $1.3 billion per year, and making LD one of the greatest threats to public health. Factors influencing the number of LD cases range from environmental to system-level variables, but little is known about the influence of vegetation (canopy, understory, and ground cover) and human behavioral risk on LD cases and exposure to infected ticks. We determined the influence of various risk factors on the risk of exposure to infected ticks on 22 different walkways using multinomial logistic regression. The model classifies the walkways into high-risk and low-risk categories with 90% accuracy, in which the understory, human risk, and number of rodents are significant indicators. These factors should be managed to control the risk of transmission of LD to humans.