Expansion of the Lyme Disease Vector Ixodes Scapularis in Canada Inferred from CMIP5 Climate Projections

Extreme precipitation, exacerbated by anthropogenic climate change, drove Peru's record-breaking 2023 dengue outbreak

Anthropogenic forcing is increasing the likelihood and severity of certain extreme weather events, which may catalyze outbreaks of climate-sensitive infectious diseases. Extreme precipitation events can promote the spread of mosquito-borne illnesses by creating vector habitat, destroying infrastructure, and impeding vector control. Here, we focus on Cyclone Yaku, which caused heavy rainfall in northwestern Peru from March 7th - 20th, 2023 and was followed by the worst dengue outbreak in Peru's history. We apply generalized synthetic control methods to account for baseline climate variation and unobserved confounders when estimating the causal effect of Cyclone Yaku on dengue cases across the 56 districts with the greatest precipitation anomalies. We estimate that 67 (95% CI: 30 - 87) % of cases in cyclone-affected districts were attributable to Cyclone Yaku. The cyclone significantly increased cases for over six months, causing 38,209 (95% CI: 17,454 - 49,928) out of 57,246 cases. The largest increases in dengue incidence due to Cyclone Yaku occurred in districts with a large share of low-quality roofs and walls in residences, greater flood risk, and warmer temperatures above 24°C. Analyzing an ensemble of climate model simulations, we found that extremely intense March precipitation in northwestern Peru is 42% more likely in the current era compared to a preindustrial baseline due to climate forcing. In sum, extreme precipitation like that associated with Cyclone Yaku has become more likely with climate change, and Cyclone Yaku caused the majority of dengue cases across the cyclone-affected districts.

Global risk dynamics of Borrelia miyamotoi in the context of climate change

The impact of Borrelia miyamotoi on human health, facilitated by the expanding geographical distribution and increasing population of Ixodes ticks, remains obscure in the context of global climate change. We employed multiple models to evaluate the effect of global climate change on the risk of B. miyamotoi worldwide across various scenarios. The habitat suitability index of four primary vector tick species for B. miyamotoi, including Ixodes persulcatus, Ixodes ricinus, Ixodes pacificus and Ixodes scapularis, was projected using a boosted regression tree model, considering multiple shared socio-economic pathway scenarios over various time periods. The modelling analysis reveals that, apart from I. scapularis, future global warming will result in a northward shift in the other three vector tick species and a gradual reduction in suitable habitats. Random forest models indicate consistent changes in B. miyamotoi and its primary tick species, with potential risk areas shrinking and shifting northward, particularly in the eastern USA, northeastern and northern Europe and northeast Asia. These findings highlight the urgent need for enhanced active surveillance of B. miyamotoi infection in primary vector tick species across projected potential risk areas. The effect of climate change on B. miyamotoi distribution might have significant implications for public health decision-making regarding tick-borne pathogens.

Age- and Sex-Specific Differences in Lyme Disease Health-Related Behaviors, Ontario, Canada, 2015-2022

We investigated differences in risk factors and preventive behaviors by age and sex among persons with reported Lyme disease in Ontario, Canada, during 2015-2022. Incidence rates peaked among children 5-9 and adults 50-79 years of age. Median age was higher for female than male case-patients (54 vs. 51 years). Male case-patients reported more activity in wooded and tall grass areas than did female case-patients; fewer male case-patients reported sharing living space with outdoor-exposed companion animals. As age increased, more case-patients reported activity in blacklegged tick habitats, exposure to ticks, and wearing adequate clothing, but fewer reported sharing living space with outdoor-exposed companion animals. Adoption of preventive behaviors was relatively low and did not differ by sex. Male case-patients, children 5-9 years of age and their parents or caregivers, and adults >59 years of age represent populations that would benefit from tailored public health messaging on Lyme disease prevention.

Models and data used to predict the abundance and distribution of Ixodes scapularis (blacklegged tick) in North America: a scoping review

Tick-borne diseases (TBD) remain prevalent worldwide, and risk assessment of tick habitat suitability is crucial to prevent or reduce their burden. This scoping review provides a comprehensive survey of models and data used to predict I. scapularis distribution and abundance in North America. We identified 4661 relevant primary research articles published in English between January 1st, 2012, and July 18th, 2022, and selected 41 articles following full-text review. Models used data-driven and mechanistic modelling frameworks informed by diverse tick, hydroclimatic, and ecological variables. Predictions captured tick abundance (n = 14, 34.1%), distribution (n = 22, 53.6%) and both (n = 5, 12.1%). All studies used tick data, and many incorporated both hydroclimatic and ecological variables. Minimal host- and human-specific data were utilized. Biases related to data collection, protocols, and tick data quality affect completeness and representativeness of prediction models. Further research and collaboration are needed to improve prediction accuracy and develop effective strategies to reduce TBD.

Knowledge, protective behaviours, and perception of Lyme disease in an area of emerging risk: results from a cross-sectional survey of adults in Ottawa, Ontario

BACKGROUND

The number of Lyme disease risk areas in Canada is growing. In regions with emerging tick populations, it is important to emphasize peridomestic risk and the importance of protective behaviours in local public health communication. This study aims to identify characteristics associated with high levels of Lyme disease knowledge and adoption of protective behaviours among residents in the Ottawa, Ontario region.

METHODS

A geographically stratified web survey was conducted in November 2020 (n = 2018) to determine knowledge, attitudes, and practices regarding Lyme disease among adult residents. Responses were used to calculate: (i) composite scores for knowledge and adoption of protective practices; and (ii) an exposure risk index based on reported activity in woodlands during the spring-to-fall tick exposure risk period.

RESULTS

60% of respondents had a high knowledge of Lyme disease, yet only 14% indicated they often use five or more measures to protect themselves. Factors strongly associated with a high level of Lyme disease knowledge included being 55 or older (Odds Ratio (OR) = 2.04), living on a property with a yard (OR = 3.22), having a high exposure index (OR = 1.59), and knowing someone previously infected with Lyme disease (OR = 2.05). Strong associations with the adoption of a high number of protective behaviours were observed with membership in a non-Indigenous racialized group (OR = 1.70), living on a property with a yard (OR = 2.37), previous infection with Lyme disease (OR = 2.13), prior tick bite exposure (OR = 1.62), and primarily occupational activity in wooded areas (OR = 2.31).

CONCLUSIONS

This study highlights the dynamics between Lyme disease knowledge, patterns of exposure risk awareness, and vigilance of personal protection in a Canadian region with emerging Lyme disease risk. Notably, this study identified gaps between perceived local risk and protective behaviours, presenting opportunities for targeted enhanced communication efforts in areas of Lyme disease emergence.

Estimating the Incidence and Economic Cost of Lyme Disease Cases in Canada in the 21st Century with Projected Climate Change

BACKGROUND

Lyme disease (LD) is emerging in Canada owing to the range expansion of the tick vector Ixodes scapularis (I. scapularis).

OBJECTIVES

Our objective was to estimate future LD incidence in Canada, and economic costs, for the 21st century with projected climate change.

METHODS

Future regions of climatic suitability for I. scapularis were projected from temperature output of the North American Coordinated Regional Climate Downscaling Experiment regional climate model ensemble using greenhouse gas Representative Concentration Pathways (RCPs) 4.5 and 8.5. Once regions became climatically suitable for ticks, an algorithm derived from tick and LD case surveillance data projected subsequent increasing LD incidence. Three scenarios (optimistic, intermediate, and pessimistic) for maximum incidence at endemicity were selected based on LD surveillance, and underreporting estimates, from the United States. Health care and productivity cost estimates of LD cases were obtained from the literature.

RESULTS

Projected annual LD cases for Canada ranged from 120,000 to > 500,000 by 2050. Variation in incidence was mostly due to the maximum incidence at endemicity selected, with minor contributions from variations among climate models and RCPs. Projected annual costs were substantial, ranging from CA $ 0.5  billion to $ 2.0  billion a year by 2050. There was little difference in projected incidence and economic cost between RCPs, and from 2050 to 2100, because projected climate up to 2050 is similar for RCP4.5 and RCP8.5 (mitigation of greenhouse gas emissions captured in RCP4.5 does not impact climate before the 2050s) and by 2050 the most densely populated areas of the study region are projected to be climatically suitable for ticks.

CONCLUSIONS

Future incidence and economic costs of LD in Canada are likely to be substantial, but uncertainties remain. Because densely populated areas of Canada are projected to become endemic under conservative climate change scenarios, mitigation of greenhouse gas emissions is unlikely to provide substantial health co-benefits for LD. https://doi.org/10.1289/EHP13759.

Planetary Health: Preparing Nursing Students for the Future

BACKGROUND

Climate change around the globe is impacting human and planetary health at unprecedented rates. Nurses are well positioned to act as climate leaders, given their critical role globally.

PROBLEM

Current and future nurses must work to mitigate climate-related health effects. It is necessary that a planetary health approach is integrated into nursing education.

APPROACH

Curricular modifications, using the Planetary Health Education Framework, are presented, which will promote awareness and understanding of climate health among future nurses. The framework is grounded in equity, which is well suited to nursing education, and can be readily adapted into current nursing curricula.

OUTCOMES

Recommendations for nursing education are presented within the 5 domains of the framework.

CONCLUSIONS

Future nurses are called on to be exemplary planetary health communicators, educators, advocates, and leaders. The Planetary Health Education Framework promotes nursing leadership in practice and in advocating for a climate-resistant future.

Establishment and range expansion of Dermacentor variabilis in the northern Maritimes of Canada: Community participatory science documents establishment of an invasive tick species

Tick populations are dependent on a complex interplay of abiotic and biotic influences, many of which are influenced by anthropic factors including climate change. Dermacentor variabilis, the wood tick or American dog tick, is a hardy tick species that feeds from a wide range of mammals and birds that can transmit pathogens of medical and agricultural importance. Significant range expansion across North America has been occurring over the past decades;this study documents northwards range expansion in the Canadian Maritime provinces. Tick recoveries from passive surveillance between 2012 and 2021 were examined to assess northward population expansion through Atlantic Canada. At the beginning of this period, D. variabilis was abundant in the most southerly province, Nova Scotia, but was not considered established in the province to the north, New Brunswick. During the 10-year span covered by this study, an increasing number of locally acquired ticks were recovered in discrete foci, suggesting small established or establishing populations in southern and coastal New Brunswick. The pattern of population establishment follows the climate-driven establishment pattern of Ixodes scapularis to some extent but there is also evidence of successful seeding of disjunct populations in areas identified as sub-optimal for tick populations. Dogs were the most common host from which these ticks were recovered, which raises the possibility of human activity, via movement of companion animals, having a significant role in establishing new populations of this species. Dermacentor variabilis is a vector of several pathogens of medical and agricultural importance but is not considered to be a competent vector for Borrelia burgdorferi, the etiological agent of Lyme disease; our molecular analysis of a subset of D. variabilis for both B. burgdorferi and B. miyamotoi did not confirm any with Borrelia. This study spans the initial establishment of this tick species and documents the pattern of introduction, providing a relatively unique opportunity to examine the first stages of range expansion of a tick species.

Mitigating the effects of climate change on human health with vaccines and vaccinations

Climate change represents an unprecedented threat to humanity and will be the ultimate challenge of the 21st century. As a public health consequence, the World Health Organization estimates an additional 250,000 deaths annually by 2030, with resource-poor countries being predominantly affected. Although climate change's direct and indirect consequences on human health are manifold and far from fully explored, a growing body of evidence demonstrates its potential to exacerbate the frequency and spread of transmissible infectious diseases. Effective, high-impact mitigation measures are critical in combating this global crisis. While vaccines and vaccination are among the most cost-effective public health interventions, they have yet to be established as a major strategy in climate change-related health effect mitigation. In this narrative review, we synthesize the available evidence on the effect of climate change on vaccine-preventable diseases. This review examines the direct effect of climate change on water-related diseases such as cholera and other enteropathogens, helminthic infections and leptospirosis. It also explores the effects of rising temperatures on vector-borne diseases like dengue, chikungunya, and malaria, as well as the impact of temperature and humidity on airborne diseases like influenza and respiratory syncytial virus infection. Recent advances in global vaccine development facilitate the use of vaccines and vaccination as a mitigation strategy in the agenda against climate change consequences. A focused evaluation of vaccine research and development, funding, and distribution related to climate change is required.

It's about time: small mammal communities and Lyme disease emergence

Theory predicts that biodiversity changes due to climate warming can mediate the rate of disease emergence. The mechanisms linking biodiversity-disease relationships have been described both theoretically and empirically but remain poorly understood. We investigated the relations between host diversity and abundance and Lyme disease risk in southern Quebec, a region where Lyme disease is rapidly emerging. We found that both the abundance of small mammal hosts and the relative abundance of the tick's natural host, the white-footed mouse (Peromyscus leucopus), influenced measures of disease risk in tick vectors (Borrelia burgdorferi infection abundance and prevalence in tick vectors). Our results suggest that the increase in Lyme disease risk is modulated by regional processes involving the abundance and composition of small mammal assemblages. However, the nature and strength of these relationships was dependent both on time and geographic area. The strong effect of P. leucopus abundance on disease risk we report here is of significant concern, as this competent host is predicted to increase in abundance and occurrence in the region, with the northern shift in the range of North American species under climate warming.

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.

Nurses' perceptions of climate sensitive vector-borne diseases: A scoping review

OBJECTIVE

Nurses are well positioned to play an integral role in the mitigation of climate change and climate-driven vector-borne diseases, however, they lack awareness and knowledge about their role. The purpose of this scoping review was to map existing literature on nurses' perceptions, knowledge, attitudes, and experiences with vector-borne diseases, specifically Lyme disease and West Nile virus.

DESIGN

A scoping review was conducted using Joanna Briggs Institute (JBI) scoping review methodology. CINAHL, ProQuest Nursing & Allied Health Premium, MEDLINE, APA PsycINFO, ProQuest Dissertations & Theses, and Web of Science were searched for English-language publications. The PRISMA-ScR was used. After initial screening as per study protocol, a total of 33 items were reviewed independently by four reviewers.

RESULTS

Thirty-three articles, including seven sources from grey literature, met the criteria for this scoping review. Results were mapped according to the five domains of the Guidelines for Undergraduate Nursing Education on Climate-Driven Vector-Borne Diseases.

CONCLUSIONS

Findings from the review indicate that nurses play a role in climate-related health effects and should be knowledgeable about vector-borne diseases. However, scant literature exists on nurses' knowledge, perceptions, attitudes toward vector-borne diseases, and practice readiness, signifying a need for further research on this emerging topic.

Epidemiology of ticks submitted from human hosts in Alberta, Canada (2000-2019)

ABSTRACTThe geographic range and occurrence of tick species is dynamic. This has important public health implications due to important tick species that can transmit pathogens. This study presents a retrospective review of tick genera recovered from humans and submitted for identification in Alberta, Canada, over a 19-year period. The total number of ticks and proportion of genera were analyzed over time. Molecular testing for a number of pathogens associated with Ixodes scapularis and I. pacificus was conducted. A total of 2,358 ticks were submitted between 2000 and 2019, with 98.6% being acquired in Alberta. The number of ticks submitted increased significantly over time (p < 0.0001). Dermacentor ticks were the most abundant genus, followed by Ixodes and Amblyomma. There was a significant decrease in the proportion of Dermacentor ticks between 2013 and 2019 (p = 0.02), with a corresponding increase in the proportion of Ixodes ticks over the same time (p = 0.04). No statistically significant change in seasonality was identified. Borrelia burgdorferi was detected in 8/76 (10.5%; 95% CI 5.4-19.4%) of all I. scapularis and I. pacificus ticks submitted. This translated to a B. burgdorferi positivity of 0.35% (95% CI 0.15-0.68%) among all ticks received. Dermacentor species (especially D. andersoni) remains the most common tick feeding on humans in Alberta. Small numbers of vector species (including I. scapularis/pacificus) are encountered annually over widely separated geographic areas in the province. The risk of exposure to tick-borne pathogens (e.g. Lyme disease) in Alberta remains low.

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.

Climate Change and Cascading Risks from Infectious Disease

Climate change is adversely affecting the burden of infectious disease throughout the world, which is a health security threat. Climate-sensitive infectious disease includes vector-borne diseases such as malaria, whose transmission potential is expected to increase because of enhanced climatic suitability for the mosquito vector in Asia, sub-Saharan Africa, and South America. Climatic suitability for the mosquitoes that can carry dengue, Zika, and chikungunya is also likely to increase, facilitating further increases in the geographic range and longer transmission seasons, and raising concern for expansion of these diseases into temperate zones, particularly under higher greenhouse gas emission scenarios. Early spring temperatures in 2018 seem to have contributed to the early onset and extensive West Nile virus outbreak in Europe, a pathogen expected to expand further beyond its current distribution, due to a warming climate. As for tick-borne diseases, climate change is projected to continue to contribute to the spread of Lyme disease and tick-borne encephalitis, particularly in North America and Europe. Schistosomiasis is a water-borne disease and public health concern in Africa, Latin America, the Middle East, and Southeast Asia; climate change is anticipated to change its distribution, with both expansions and contractions expected. Other water-borne diseases that cause diarrheal diseases have declined significantly over the last decades owing to socioeconomic development and public health measures but changes in climate can reverse some of these positive developments. Weather and climate events, population movement, land use changes, urbanization, global trade, and other drivers can catalyze a succession of secondary events that can lead to a range of health impacts, including infectious disease outbreaks. These cascading risk pathways of causally connected events can result in large-scale outbreaks and affect society at large. We review climatic and other cascading drivers of infectious disease with projections under different climate change scenarios. Supplementary file1 (MP4 328467 KB).

Effect of Land-Use Change on the Changes in Human Lyme Risk in the United States

The spatial extent and incidence of Lyme disease is increasing in the United States, particularly in the Upper Midwest and Northeast. Many previous studies have explored the drivers of its spatial pattern, however, few studies tried to explore the drivers for the changes of Lyme disease. We here compared the spatial patterns of changes of human Lyme cases and incidence in the Northeast and Upper Midwest between 2003–2005 and 2015–2017, and applied two different approaches (i.e., a statistical regularization approach and model averaging) to investigate the climatic and landscape factors affecting the risk change between the two periods. Our results suggested that changes in land-use variables generally showed different relationships with changes of human Lyme risk between the two regions. Changes of variables related to human-use areas showed opposite correlations in two regions. Besides, forest area and forest edge density generally negatively correlated with the change of human Lyme risk. In the context of ongoing habitat change, we consider this study may provide new insight into understanding the responses of human Lyme disease to these changes, and contribute to a better prediction in the future.

Flavivirus-host interactions: an expanding network of proviral and antiviral factors

Flaviviruses are zoonotic pathogens transmitted by the bite of infected mosquitos and ticks and represent a constant burden to human health. Here we review recent literature aimed at uncovering how flaviviruses interact with the cells that they infect. A better understanding of these interactions may ultimately lead to novel therapeutic targets. We highlight several studies that employed low-biased methods to discover new protein-protein, protein-RNA, and genetic interactions, and spotlight recent work characterizing the host protein, TMEM41B, which has been shown to be critical for infection by diverse flaviviruses and coronaviruses.

Ticks, Human Babesiosis and Climate Change

The effects of current and future global warming on the distribution and activity of the primary ixodid vectors of human babesiosis (caused by Babesia divergens, B. venatorum and B. microti) are discussed. There is clear evidence that the distributions of both Ixodes ricinus, the vector in Europe, and I. scapularis in North America have been impacted by the changing climate, with increasing temperatures resulting in the northwards expansion of tick populations and the occurrence of I. ricinus at higher altitudes. Ixodes persulcatus, which replaces I. ricinus in Eurasia and temperate Asia, is presumed to be the babesiosis vector in China and Japan, but this tick species has not yet been confirmed as the vector of either human or animal babesiosis. There is no definite evidence, as yet, of global warming having an effect on the occurrence of human babesiosis, but models suggest that it is only a matter of time before cases occur further north than they do at present.

Risk of transfusion-transmitted Babesia microti in Canada

BACKGROUND

Babesia microti has gained a foothold in Canada as tick vectors become established in broader geographic areas. B. microti infection is associated with mild or no symptoms in healthy individuals but is transfusion-transmissible and can be fatal in immunocompromised individuals. This is the first estimate of clinically significant transfusion-transmitted babesiosis (TTB) risk in Canada.

STUDY DESIGN AND METHODS

The proportion of B. microti-antibody (AB)/nucleic acid amplification test (NAT)-positive whole blood donations was estimated at 5.5% of the proportion of the general population with reported Lyme Disease (also tick-borne) based on US data. Monte Carlo simulation estimated the number and proportion of infectious red cell units for three scenarios: base, localized incidence (risk in Manitoba only), and donor study informed (prevalence from donor data). The model simulated 1,029,800 donations repeated 100,000 times for each.

RESULTS

In the base scenario 0.5 (0.01, 1.75), B. microti-NAT-positive donations would be expected per year, with 0.08 (0, 0.38) recipients suffering clinically significant TTB (1 every 12.5 years). In the localized incidence scenario, there were 0.21(0, 0.7) B. microti-NAT-positive donations, with 0.04 (0, 0.14) recipient infections (about 1 every 25 years). In the donor study informed scenario, there were 4.6 (0.3, 15.8) B. microti-NAT-positive donations expected, and 0.81 (0.05, 3.14) clinically significant TTB cases per year.

DISCUSSION

The likelihood of clinically relevant TTB is low. Testing would have very little utility in Canada at this time. Ongoing pathogen surveillance in tick vectors is important as B. microti prevalence appears to be slowly increasing in Canada.

Efficacy of a novel topical combination of esafoxolaner, eprinomectin and praziquantel against Ixodes ricinus and Ixodes scapularis in cats

Esafoxolaner is a purified enantiomer of afoxolaner with insecticidal and acaricidal properties. It is combined with eprinomectin and praziquantel in a novel topical endectoparasiticide formulation for cats. The efficacy of this novel formulation was evaluated in three Ixodes ricinus and two Ixodes scapularis experimental studies, with comparable designs. In each study, cats were randomly allocated, based on a pre-treatment tick infestation and count, to a placebo control group or a group treated with the minimum recommended dose of the novel formulation. Cats were infested two days before treatment and weekly thereafter. Immediate efficacy was evaluated 48 h after treatment; persistent efficacy was evaluated 48 h after new weekly infestations for at least one month after the treatment (in one of the studies, the first two weeks of persistent efficacy against I. ricinus were not tested). Efficacy was calculated at each timepoint by comparison of arithmetic means of live ticks found in the control and the treated groups. In the three studies targeting I. ricinus, immediate and persistent efficacies ranged between 91% and 100% for five weeks. In the two studies targeting I. scapularis, immediate and persistent efficacies ranged between 95% and 100%, and 98% and 100% for one month, respectively. These studies provide robust evidence of efficacy of the novel topical formulation of esafoxolaner, eprinomectin and praziquantel against experimental I. ricinus and I. scapularis infestations for at least one month in cats.

A multi-year assessment of blacklegged tick (Ixodes scapularis) population establishment and Lyme disease risk areas in Ottawa, Canada, 2017-2019

Canadians face an emerging threat of Lyme disease due to the northward expansion of the tick vector, Ixodes scapularis. We evaluated the degree of I. scapularis population establishment and Borrelia burgdorferi occurrence in the city of Ottawa, Ontario, Canada from 2017–2019 using active surveillance at 28 sites. We used a field indicator tool developed by Clow et al. to determine the risk of I. scapularis establishment for each tick cohort at each site using the results of drag sampling. Based on results obtained with the field indicator tool, we assigned each site an ecological classification describing the pattern of tick colonization over two successive cohorts (cohort 1 was comprised of ticks collected in fall 2017 and spring 2018, and cohort 2 was collected in fall 2018 and spring 2019). Total annual site-specific I. scapularis density ranged from 0 to 16.3 ticks per person-hour. Sites with the highest density were located within the Greenbelt zone, in the suburban/rural areas in the western portion of the city of Ottawa, and along the Ottawa River; the lowest densities occurred at sites in the suburban/urban core. B. burgdorferi infection rates exhibited a similar spatial distribution pattern. Of the 23 sites for which data for two tick cohorts were available, 11 sites were classified as “high-stable”, 4 were classified as “emerging”, 2 were classified as “low-stable”, and 6 were classified as “non-zero”. B. burgdorferi-infected ticks were found at all high-stable sites, and at one emerging site. These findings suggest that high-stable sites pose a risk of Lyme disease exposure to the community as they have reproducing tick populations with consistent levels of B. burgdorferi infection. Continued surveillance for I. scapularis, B. burgdorferi, and range expansion of other tick species and emerging tick-borne pathogens is important to identify areas posing a high risk for human exposure to tick-borne pathogens in the face of ongoing climate change and urban expansion.

Impact of prior and projected climate change on US Lyme disease incidence

Lyme disease is the most common vector-borne disease in temperate zones and a growing public health threat in the United States (US). The life cycles of the tick vectors and spirochete pathogen are highly sensitive to climate, but determining the impact of climate change on Lyme disease burden has been challenging due to the complex ecology of the disease and the presence of multiple, interacting drivers of transmission. Here we incorporated 18 years of annual, county-level Lyme disease case data in a panel data statistical model to investigate prior effects of climate variation on disease incidence while controlling for other putative drivers. We then used these climate-disease relationships to project Lyme disease cases using CMIP5 global climate models and two potential climate scenarios (RCP4.5 and RCP8.5). We find that interannual variation in Lyme disease incidence is associated with climate variation in all US regions encompassing the range of the primary vector species. In all regions, the climate predictors explained less of the variation in Lyme disease incidence than unobserved county-level heterogeneity, but the strongest climate-disease association detected was between warming annual temperatures and increasing incidence in the Northeast. Lyme disease projections indicate that cases in the Northeast will increase significantly by 2050 (23,619 ± 21,607 additional cases), but only under RCP8.5, and with large uncertainty around this projected increase. Significant case changes are not projected for any other region under either climate scenario. The results demonstrate a regionally variable and nuanced relationship between climate change and Lyme disease, indicating possible nonlinear responses of vector ticks and transmission dynamics to projected climate change. Moreover, our results highlight the need for improved preparedness and public health interventions in endemic regions to minimize the impact of further climate change-induced increases in Lyme disease burden.

TMEM41B Is a Pan-flavivirus Host Factor

Flaviviruses pose a constant threat to human health. These RNA viruses are transmitted by the bite of infected mosquitoes and ticks and regularly cause outbreaks. To identify host factors required for flavivirus infection, we performed full-genome loss of function CRISPR-Cas9 screens. Based on these results, we focused our efforts on characterizing the roles that TMEM41B and VMP1 play in the virus replication cycle. Our mechanistic studies on TMEM41B revealed that all members of the Flaviviridae family that we tested require TMEM41B. We tested 12 additional virus families and found that SARS-CoV-2 of the Coronaviridae also required TMEM41B for infection. Remarkably, single nucleotide polymorphisms present at nearly 20% in East Asian populations reduce flavivirus infection. Based on our mechanistic studies, we propose that TMEM41B is recruited to flavivirus RNA replication complexes to facilitate membrane curvature, which creates a protected environment for viral genome replication.

The Impacts of Climate Change on Ticks and Tick-Borne Disease Risk

Ticks exist on all continents and carry more zoonotic pathogens than any other type of vector. Ticks spend most of their lives in the external environment away from the host and are thus expected to be affected by changes in climate. Most empirical and theoretical studies demonstrate or predict range shifts or increases in ticks and tick-borne diseases, but there can be a lot of heterogeneity in such predictions. Tick-borne disease systems are complex, and determining whether changes are due to climate change or other drivers can be difficult. Modeling studies can help tease apart and understand the roles of different drivers of change. Predictive models can also be invaluable in projecting changes according to different climate change scenarios. However, validating these models remains challenging, and estimating uncertainty in predictions is essential. Another focus for future research should be assessing the resilience of ticks and tick-borne pathogens to climate change.

TMEM41B is a pan-flavivirus host factor

Flaviviruses pose a constant threat to human health. These RNA viruses are transmitted by the bite of infected mosquitoes and ticks and regularly cause outbreaks. To identify host factors required for flavivirus infection we performed full-genome loss of function CRISPR-Cas9 screens. Based on these results we focused our efforts on characterizing the roles that TMEM41B and VMP1 play in the virus replication cycle. Our mechanistic studies on TMEM41B revealed that all members of the Flaviviridae family that we tested require TMEM41B. We tested 12 additional virus families and found that SARS-CoV-2 of the Coronaviridae also required TMEM41B for infection. Remarkably, single nucleotide polymorphisms (SNPs) present at nearly twenty percent in East Asian populations reduce flavivirus infection. Based on our mechanistic studies we hypothesize that TMEM41B is recruited to flavivirus RNA replication complexes to facilitate membrane curvature, which creates a protected environment for viral genome replication.

HIGHLIGHTS

TMEM41B and VMP1 are required for both autophagy and flavivirus infection, however, autophagy is not required for flavivirus infection.TMEM41B associates with viral proteins and likely facilitates membrane remodeling to establish viral RNA replication complexes.TMEM41B single nucleotide polymorphisms (SNPs) present at nearly twenty percent in East Asian populations reduce flavivirus infection.TMEM41B-deficient cells display an exaggerated innate immune response upon high multiplicity flavivirus infection.

Development and validation of a behavioral index for adaptation to lyme disease

Background

Recent evidence suggests that climate change and other factors are leading to the emergence of Lyme disease in the province of Quebec, where it previously did not exist. As risk areas expand further north, the population can adopt specific preventive behaviors to limit chances of infection. The objectives of this study were to (1) create an index of Lyme disease prevention behaviors (LDPB), and (2) use the theory of planned behavior (TPB) to explain the decision-making process of people who choose to adopt LDPB.

Methods

A sample of 1959 adults living in a Lyme disease risk area completed a questionnaire by phone (n = 1003) or on the Web (n = 956). The questionnaire measured whether they did or did not adopt the LDPB proposed by public health officials. It also measured some TPB variables, including their attitude or perceived social norms regarding LDPB.

Results

Our findings led to the creation of a Lyme disease prevention index consisting of 10 behaviors, down from the 19 behaviors initially considered for inclusion in the index. Rates of adoption of each behavior varied tremendously, from 4.30 to 83.80%. All variables of the TPB model (attitude, social norms, and perceived control) were significantly associated with intention to adopt preventive behaviors. Intention itself was significantly associated with adoption of LDPB. Likewise, risk perception was positively correlated with the adoption of LDPB.

Conclusions

This study led to the creation of a Lyme disease prevention index that can be used by public health agencies, researchers, and professionals to monitor the evolution over time of individuals’ LDPB adoption rates. It also showed the usefulness of the TPB in understanding the adoption of LDPB and how intention to adopt such behaviors is formed.

Telephone versus web panel National Survey for monitoring adoption of preventive behaviors to climate change in populations: a case study of Lyme disease in Québec, Canada

BACKGROUND

To monitor the adoption of climate change adaptive behaviors in the population, public health authorities have to conduct national surveys, which can help them target vulnerable subpopulations. To ensure reliable estimates of the adoption of these preventive behaviors, many data collection methods are offered by polling firms. The aim of this study was to compare a telephone survey with a web survey on Lyme disease with regard to their representativeness.

METHODS

The data comes from a cross-sectional study conducted in the Province of Québec (Canada). In total, 1003 people completed the questionnaire by telephone and 956 filled in a web questionnaire. We compared the data obtained from both survey modes with the census data in regard to various demographic characteristics. We then compared the data from both samples in terms of self-reported Lyme disease preventive behaviors and other theoretically associated constructs. We also assessed the measurement invariance (equivalence) of the index of Lyme disease preventive behaviors across the telephone and web samples.

RESULTS

Findings showed that neither the telephone nor the web panel modes of data collection can be considered more representative of the target population. The results showed that the proportion of item non-responses was significantly higher with the web questionnaire (5.6%) than with the telephone survey (1.3%), and that the magnitude of the differences between the two survey modes was nil for 19 out of the 30 items related to Lyme disease, and small for 11 of them. Results from invariance analyses confirmed the measurement invariance of an index of adaptation to Lyme disease, as well as the mean invariance across both samples.

CONCLUSIONS

Our results suggested that both samples provided similar estimates of the level of adaptation to Lyme disease preventive behaviors. In sum, the results of our study showed that neither survey mode was superior to the other. Thus, in studies where adaptation to climate change is monitored over time, using a web survey instead of a telephone survey could be more cost-effective, and researchers should consider doing so in future surveys on adaptation to climate. However, we recommend conducting a pretest study before deciding whether to use both survey modes or only one of them.

Zoonotic Babesia: A scoping review of the global evidence

BACKGROUND

Babesiosis is a parasitic vector-borne disease of increasing public health importance. Since the first human case was reported in 1957, zoonotic species have been reported on nearly every continent. Zoonotic Babesia is vectored by Ixodes ticks and is commonly transmitted in North America by Ixodes scapularis, the tick species responsible for transmitting the pathogens that also cause Lyme disease, Powassan virus, and anaplasmosis in humans. Predicted climate change is expected to impact the spread of vectors, which is likely to affect the distribution of vector-borne diseases including human babesiosis.

METHODS

A scoping review has been executed to characterize the global evidence on zoonotic babesiosis. Articles were compiled through a comprehensive search of relevant bibliographic databases and targeted government websites. Two reviewers screened titles and abstracts for relevance and characterized full-text articles using a relevance screening and data characterization tool developed a priori.

RESULTS

This review included 1394 articles relevant to human babesiosis and/or zoonotic Babesia species. The main zoonotic species were B. microti, B. divergens, B. duncani and B. venatorum. Articles described a variety of study designs used to study babesiosis in humans and/or zoonotic Babesia species in vectors, animal hosts, and in vitro cell cultures. Topics of study included: pathogenesis (680 articles), epidemiology (480), parasite characterization (243), diagnostic test accuracy (98), mitigation (94), treatment (65), transmission (54), surveillance (29), economic analysis (7), and societal knowledge (1). No articles reported predictive models investigating the impact of climate change on Babesia species.

CONCLUSION

Knowledge gaps in the current evidence include research on the economic burden associated with babesiosis, societal knowledge studies, surveillance of Babesia species in vectors and animal hosts, and predictive models on the impact of climate change. The scoping review results describe the current knowledge and knowledge gaps on zoonotic Babesia which can be used to inform future policy and decision making.

THE EXPOSOME IN HUMAN EVOLUTION: FROM DUST TO DIESEL

Global exposures to air pollution and cigarette smoke are novel in human evolutionary history and are associated with about 16 million premature deaths per year. We investigate the history of the human exposome for relationships between novel environmental toxins and genetic changes during human evolution in six phases. Phase I: With increased walking on savannas, early human ancestors inhaled crustal dust, fecal aerosols, and spores; carrion scavenging introduced new infectious pathogens. Phase II: Domestic fire exposed early Homo to novel toxins from smoke and cooking. Phases III and IV: Neolithic to preindustrial Homo sapiens incurred infectious pathogens from domestic animals and dense communities with limited sanitation. Phase V: Industrialization introduced novel toxins from fossil fuels, industrial chemicals, and tobacco at the same time infectious pathogens were diminishing. Thereby, pathogen-driven causes of mortality were replaced by chronic diseases driven by sterile inflammogens, exogenous and endogenous. Phase VI: Considers future health during global warming with increased air pollution and infections. We hypothesize that adaptation to some ancient toxins persists in genetic variations associated with inflammation and longevity.

Effect of Rising Temperature on Lyme Disease: Ixodes scapularis Population Dynamics and Borrelia burgdorferi Transmission and Prevalence

Warmer temperatures are expected to increase the incidence of Lyme disease through enhanced tick maturation rates and a longer season of transmission. In addition, there could be an increased risk of disease export because of infected mobile hosts, usually birds. A temperature-driven seasonal model of Borrelia burgdorferi (Lyme disease) transmission among four host types is constructed as a system of nonlinear ordinary differential equations. The model is developed and parametrized based on a collection of lab and field studies. The model is shown to produce biologically reasonable results for both the tick vector (Ixodes scapularis) and the hosts when compared to a different set of studies. The model is used to predict the response of Lyme disease risk to a mean annual temperature increase, based on current temperature cycles in Hanover, NH. Many of the risk measures suggested by the literature are shown to change with increased mean annual temperature. The most straightforward measure of disease risk is the abundance of infected questing ticks, averaged over a year. Compared to this measure, which is difficult and resource-intensive to track in the field, all other risk measures considered underestimate the rise of risk with rise in mean annual temperature. The measure coming closest was “degree days above zero.” Disease prevalence in ticks and hosts showed less increase with rising temperature. Single field measurements at the height of transmission season did not show much change at all with rising temperature.

Could nature help children rise out of poverty? Green space and future earnings from a cohort in ten U.S. cities

BACKGROUND

Growing up in poverty is associated with poor health, and the American Dream of upward mobility is becoming an illusion for many low-income children. But nearby green space can support academic achievement, creativity, and emotional regulation, and these traits might help children rise out of poverty.

OBJECTIVES

To examine the relationship between recent incomes of children born into poverty in the ten largest U.S. cities and densities of residential green space during childhood.

METHODS

We calculate park proximity, park acreage, new park development, and NDVI greenness for 1980-1990 from Landsat and Trust for Public Land data. We obtain the 2014 income for children born between 1978 and 1982 into families in poverty from The Opportunity Atlas cohort, aggregated at the tract level (n = 5849).

RESULTS

Conditional autoregressive (CAR) models of tracts show statistically significant associations between income rank and above-average levels of greenness but not between income rank and park measures, adjusting for individual and neighborhood confounders and spatial autocorrelation. We estimate that, over a 30-year career, children growing up in tracts with the most vegetative cover will earn cumulatively $28,000 more than children growing up in tracts with the least cover, on average. Tracts with lower than average levels of precipitation, higher disadvantage, higher population density, or higher annual temperatures do not show beneficial effects of green space.

CONCLUSIONS

Greenness may be weakly associated with children rising out of poverty in wetter, cooler, less-dense, more advantaged census tracts.

Lyme Disease Risks in Europe under Multiple Uncertain Drivers of Change

BACKGROUND

Debates over whether climate change could lead to the amplification of Lyme disease (LD) risk in the future have received much attention. Although recent large-scale disease mapping studies project an overall increase in Lyme disease risk as the climate warms, such conclusions are based on climate-driven models in which other drivers of change, such as land-use/cover and host population distribution, are less considered.

OBJECTIVES

The main objectives were to project the likely future ecological risk patterns of LD in Europe under different assumptions about future socioeconomic and climate conditions and to explore similarity and uncertainty in the projected risks.

METHODS

An integrative, spatially explicit modeling study of the ecological risk patterns of LD in Europe was conducted by applying recent advances in process-based modeling of tick-borne diseases, species distribution mapping, and scenarios of land-use/cover change. We drove the model with stakeholder-driven, integrated scenarios of plausible future socioeconomic and climate change [the Shared Socioeconomic Pathway (SSPs) combined with the Representative Concentration Pathways (RCPs)].

RESULTS

The model projections suggest that future temperature increases may not always amplify LD risk: Low emissions scenarios (RCP2.6) combined with a sustainability socioeconomic scenario (SSP1) resulted in reduced LD risk. The greatest increase in risk was projected under intermediate (RCP4.5) rather than high-end (RCP8.5) climate change scenarios. Climate and land-use change were projected to have different roles in shaping the future regional dynamics of risk, with climate warming being likely to cause risk expansion in northern Europe and conversion of forest to agriculture being likely to limit risk in southern Europe.

CONCLUSIONS

Projected regional differences in LD risk resulted from mixed effects of temperature, land use, and host distributions, suggesting region-specific and cross-sectoral foci for LD risk management policy. The integrated model provides an improved explanatory tool for the system mechanisms of LD pathogen transmission and how pathogen transmission could respond to combined socioeconomic and climate changes. https://doi.org/10.1289/EHP4615.

Risk assessment strategies for early detection and prediction of infectious disease outbreaks associated with climate change

A new generation of surveillance strategies is being developed to help detect emerging infections and to identify the increased risks of infectious disease outbreaks that are expected to occur with climate change. These surveillance strategies include event-based surveillance (EBS) systems and risk modelling. The EBS systems use open-source internet data, such as media reports, official reports, and social media (such as Twitter) to detect evidence of an emerging threat, and can be used in conjunction with conventional surveillance systems to enhance early warning of public health threats. More recently, EBS systems include artificial intelligence applications such machine learning and natural language processing to increase the speed, capacity and accuracy of filtering, classifying and analysing health-related internet data. Risk modelling uses statistical and mathematical methods to assess the severity of disease emergence and spread given factors about the host (e.g. number of reported cases), pathogen (e.g. pathogenicity) and environment (e.g. climate suitability for reservoir populations). The types of data in these models are expanding to include health-related information from open-source internet data and information on mobility patterns of humans and goods. This information is helping to identify susceptible populations and predict the pathways from which infections might spread into new areas and new countries. As a powerful addition to traditional surveillance strategies that identify what has already happened, it is anticipated that EBS systems and risk modelling will increasingly be used to inform public health actions to prevent, detect and mitigate the climate change increases in infectious diseases.

Estimating direct healthcare costs attributable to laboratory-confirmed Lyme disease in Ontario, Canada: A population-based matched cohort study using health administrative data

The objective of this study was to determine healthcare costs attributable to laboratory-confirmed Lyme disease (LD) from the healthcare payer perspective in Ontario, Canada. A cost-of-illness study was conducted for incident LD subjects from 1 January 2006 through 31 December 2013 ascertained from provincial laboratory and reportable disease databases, linked to health administrative data. All LD subjects included were laboratory-confirmed, according to provincial case definitions. Incident LD subjects were propensity-score matched to uninfected subjects on age, sex, comorbidities and urban/rural status. We used phase-of-care methods to calculate attributable costs for two phases of illness: initial care (≤30 days following "index date") and continuing care (>30 days after index date to the end of the follow-up period). A total of 663 incident, confirmed LD subjects were identified from 2006 through 2013. Mean age was 44.2 ± 20.1 years; 339 (51.1%) were female; and 31 (4.7%) were hospitalized ≤30 days after index date. Six hundred fifty-eight (99.2%) LD subjects were matched to uninfected subjects; mean follow-up time was 3.3 years. Mean attributable costs per case during the initial care phase and continuing care were $277 (95% CI: $197, $357) and -$5 (-$27, $17), respectively. Attributable costs per LD subject aged 5-14 years were $440 ($132, $747), greater than the costs observed for other age strata. Expected 1-year attributable costs were $832, given continuing care costs were negligible. Limitations to our study include estimating costs using a cohort of only laboratory-confirmed LD cases, introducing selection bias for diagnosed and treated patients who may have a lower risk of developing sequelae. In conclusion, the initial care phase of LD is associated with increased healthcare costs, but without significant costs attributable to LD infection after 30 days. Estimates of costs attributable to LD are important for healthcare resource prioritization and the evaluation of novel interventions.

Impact of recent and future climate change on vector-borne diseases

Climate change is one of the greatest threats to human health in the 21st century. Climate directly impacts health through climatic extremes, air quality, sea-level rise, and multifaceted influences on food production systems and water resources. Climate also affects infectious diseases, which have played a significant role in human history, impacting the rise and fall of civilizations and facilitating the conquest of new territories. Our review highlights significant regional changes in vector and pathogen distribution reported in temperate, peri-Arctic, Arctic, and tropical highland regions during recent decades, changes that have been anticipated by scientists worldwide. Further future changes are likely if we fail to mitigate and adapt to climate change. Many key factors affect the spread and severity of human diseases, including mobility of people, animals, and goods; control measures in place; availability of effective drugs; quality of public health services; human behavior; and political stability and conflicts. With drug and insecticide resistance on the rise, significant funding and research efforts must to be maintained to continue the battle against existing and emerging diseases, particularly those that are vector borne.

"Ticking Bomb": The Impact of Climate Change on the Incidence of Lyme Disease

Lyme disease (LD) is the most common tick-borne disease in North America. It is caused by Borrelia burgdorferi and transmitted to humans by blacklegged ticks, Ixodes scapularis. The life cycle of the LD vector, I. scapularis, usually takes two to three years to complete and goes through three stages, all of which are dependent on environmental factors. Increases in daily average temperatures, a manifestation of climate change, might have contributed to an increase in tick abundance via higher rates of tick survival. Additionally, these environmental changes might have contributed to better host availability, which is necessary for tick feeding and life cycle completion. In fact, it has been shown that both tick activity and survival depend on temperature and humidity. In this study, we have examined the relationship between those climatic variables and the reported incidence of LD in 15 states that contribute to more than 95% of reported cases within the Unites States. Using fixed effects analysis for a panel of 468 U.S. counties from those high-incidence states with annual data available for the period 2000-2016, we have found sizable impacts of temperature on the incidence of LD. Those impacts can be described approximately by an inverted U-shaped relationship, consistent with patterns of tick survival and host-seeking behavior. Assuming a 2°C increase in annual average temperature-in line with mid-century (2036-2065) projections from the latest U.S. National Climate Assessment (NCA4)-we have predicted that the number of LD cases in the United States will increase by over 20 percent in the coming decades. These findings may help improving preparedness and response by clinicians, public health professionals, and policy makers, as well as raising public awareness of the importance of being cautious when engaging in outdoor activities.

Under-Detection of Lyme Disease in Canada

Lyme disease arises from infection with pathogenic Borrelia species. In Canada, current case definition for confirmed Lyme disease requires serological confirmation by both a positive first tier ELISA and confirmatory second tier immunoblot (western blot). For surveillance and research initiatives, this requirement is intentionally conservative to exclude false positive results. Consequently, this approach is prone to false negative results that lead to underestimation of the number of people with Lyme disease. The province of New Brunswick (NB), Canada, can be used to quantify under-detection of the disease as three independent data sets are available to generate an estimate of the true human disease prevalence and incidence. First, detailed human disease incidence is available for the US states and counties bordering Canada, which can be compared with Canadian disease incidence. Second, published national serology results and well-described sensitivity and specificity values for these tests are available and deductive reasoning can be used to query for discrepancies. Third, high-density tick and canine surveillance data are available for the province, which can be used to predict expected human Lyme prevalence. Comparison of cross-border disease incidence suggests a minimum of 10.2 to 28-fold under-detection of Lyme disease (3.6% to 9.8% cases detected). Analysis of serological testing predicts the surveillance criteria generate 10.4-fold under-diagnosis (9.6% cases detected) in New Brunswick for 2014 due to serology alone. Calculation of expected human Lyme disease cases based on tick and canine infections in New Brunswick indicates a minimum of 12.1 to 58.2-fold underestimation (1.7% to 8.3% cases detected). All of these considerations apply generally across the country and strongly suggest that public health information is significantly under-detecting and under-reporting human Lyme cases across Canada. Causes of the discrepancies between reported cases and predicted actual cases may include undetected genetic diversity of Borrelia in Canada leading to failed serological detection of infection, failure to consider and initiate serological testing of patients, and failure to report clinically diagnosed acute cases. As these surveillance criteria are used to inform clinical and public health decisions, this under-detection will impact diagnosis and treatment of Canadian Lyme disease patients.

Climate change and vector-borne diseases of public health significance

There has been much debate as to whether or not climate change will have, or has had, any significant effect on risk from vector-borne diseases. The debate on the former has focused on the degree to which occurrence and levels of risk of vector-borne diseases are determined by climate-dependent or independent factors, while the debate on the latter has focused on whether changes in disease incidence are due to climate at all, and/or are attributable to recent climate change. Here I review possible effects of climate change on vector-borne diseases, methods used to predict these effects and the evidence to date of changes in vector-borne disease risks that can be attributed to recent climate change. Predictions have both over- and underestimated the effects of climate change. Mostly under-estimations of effects are due to a focus only on direct effects of climate on disease ecology while more distal effects on society's capacity to control and prevent vector-borne disease are ignored. There is increasing evidence for possible impacts of recent climate change on some vector-borne diseases but for the most part, observed data series are too short (or non-existent), and impacts of climate-independent factors too great, to confidently attribute changing risk to climate change.

High-Resolution Ecological Niche Modeling of Ixodes scapularis Ticks Based on Passive Surveillance Data at the Northern Frontier of Lyme Disease Emergence in North America

BACKGROUND

Lyme disease (LD) is a bacterial infection transmitted by the black-legged tick (Ixodes scapularis) in eastern North America. It is an emerging disease in Canada due to the expanding range of its tick vector. Environmental risk maps for LD, based on the distribution of the black-legged tick, have focused on coarse determinants such as climate. However, climatic factors vary little within individual health units, the level at which local public health decision-making takes place. We hypothesize that high-resolution environmental data and routinely collected passive surveillance data can be used to develop valid models for tick occurrence and provide insight into ecological processes affecting tick presence at fine scales.

METHODS

We used a maximum entropy algorithm (MaxEnt) to build a habitat suitability model for I. scapularis in Ottawa, Ontario, Canada using georeferenced occurrence points from passive surveillance data collected between 2013 and 2016 and high-resolution land cover and elevation data. We evaluated our model using an independent tick presence/absence dataset collected through active surveillance at 17 field sites during the summer of 2017.

RESULTS

Our model showed a good ability to discriminate positive sites from negative sites for tick presence (AUC = 0.878 ± 0.019, classification accuracy = 0.835 ± 0.020). Heavily forested suburban and rural areas in the west and southwest of Ottawa had higher predicted suitability than the more agricultural eastern areas.

CONCLUSIONS

This study demonstrates the value of passive surveillance data to model local-scale environmental risk for the tick vector of LD at sites of interest to public health. Given the rising incidence of LD and other emerging vector-borne diseases in Canada, our findings support the ongoing collection of these data and collaboration with researchers to provide a timely and accurate portrait of evolving public health risk.

A field-based indicator for determining the likelihood of Ixodes scapularis establishment at sites in Ontario, Canada

The emergence of the vector Ixodes scapularis in Ontario, Canada poses a significant public health risk. Both passive and active surveillance approaches have been employed by public health professionals (i.e., government employees) to monitor for the range expansion of this tick. Field surveillance using drag sampling for questing ticks is a recognized and effective method to identify reproducing tick populations. The degree of effort (i.e., number of visits per site) can enhance the sensitivity and specificity of surveillance, but increased effort conflicts with the cost to public health for field surveillance. Here we developed an indicator to determine the likelihood of I. scapularis establishment based on field sampling results. Field data from two established populations of I. scapularis in Ontario were incorporated with previous analyses of surveillance data to create the indicator, which is in the form of a scoring system. The life stage(s) collected, overall abundance and past surveillance findings from a site are all considered and a level is assigned for the likelihood of I. scapularis establishment based on current field sampling results. The likelihood levels are non-zero (i.e., no I. scapularis detected, but risk still present due to adventitious ticks), low, medium or high, and recommendations for future surveillance and public health measures are provided. The indicator was validated against field sampling results from five other established sites in the province and correctly categorized all five areas as high likelihood of establishment. The indicator was also applied to field sampling results from 36 sites of unknown status that were visited twice during the period of 2014-2016. There was substantial agreement of levels between measurements, as calculated using a weighted kappa. The indicator can assist public health professionals with the interpretation of field sampling results and direct their efforts for ongoing surveillance and public health interventions for I. scapularis-borne diseases, including Lyme disease.

Northward range expansion of Ixodes scapularis evident over a short timescale in Ontario, Canada

The invasion of the blacklegged tick, Ixodes scapularis into Ontario, Canada poses a significant risk to public health because it is a vector for numerous pathogens, including Borrelia burgdorferi sensu stricto, the causative agent of Lyme disease. Baseline field sampling in 2014 and 2015 detected I. scapularis and B. burgdorferi at sites across southern, eastern and central Ontario, including a hot spot in eastern Ontario. A “speed of spread” model for I. scapularis developed by Leighton and colleagues (2012) estimated that the tick’s range was expanding northward at 46 km/year. In 2016, we revisited a subset of sites sampled in 2014 and 2015 to understand the changing nature of risk, and assess whether the rate of tick invasion is consistent with the speed of spread estimate. Ticks were collected via tick dragging at 17 out of 36 sites, 5 of which were new sites for I. scapularis. Samples were positive for B. burgdorferi at 8 sites. No other I. scapularis-borne pathogens were detected. Centrographic statistics revealed an increase in the dispersion of I. scapularis positive sites in eastern Ontario. Field data for each site were then compared to the model’s predicted year of establishment for each census subdivision. Our findings illustrate that the range expansion of I. scapularis and the emergence of B. burgdorferi is ongoing, and provide short timescale evidence of the processes associated with I. scapularis spread. The range front appears to be moving at a rate of ~46 km/year, with colonization of the tick behind this range front occurring at a slower and heterogeneous rate. Assessment of site-level ecological factors did not provide any insight into the underlying processes that may be influencing the colonization of I. scapularis in specific areas. Ongoing field sampling is needed to monitor this dynamic process. This study highlights the current geographic risk associated with Lyme disease, which can be used to target public health interventions to the areas of greatest risk.

Detecting and Attributing Health Burdens to Climate Change

BACKGROUND

Detection and attribution of health impacts caused by climate change uses formal methods to determine a) whether the occurrence of adverse health outcomes has changed, and b) the extent to which that change could be attributed to climate change. There have been limited efforts to undertake detection and attribution analyses in health.

OBJECTIVE

Our goal was to show a range of approaches for conducting detection and attribution analyses.

RESULTS

Case studies for heatwaves, Lyme disease in Canada, and Vibrio emergence in northern Europe highlight evidence that climate change is adversely affecting human health. Changes in rates and geographic distribution of adverse health outcomes were detected, and, in each instance, a proportion of the observed changes could, in our judgment, be attributed to changes in weather patterns associated with climate change.

CONCLUSIONS

The results of detection and attribution studies can inform evidence-based risk management to reduce current, and plan for future, changes in health risks associated with climate change. Gaining a better understanding of the size, timing, and distribution of the climate change burden of disease and injury requires reliable long-term data sets, more knowledge about the factors that confound and modify the effects of climate on health, and refinement of analytic techniques for detection and attribution. At the same time, significant advances are possible in the absence of complete data and statistical certainty: there is a place for well-informed judgments, based on understanding of underlying processes and matching of patterns of health, climate, and other determinants of human well-being. https://doi.org/10.1289/EHP1509.