Estimated effects of projected climate change on the basic reproductive number of the Lyme disease vector Ixodes scapularis

Risk of Development of Chronic Kidney Disease After Exposure to Borrelia burgdorferi and Anaplasma spp

Lyme disease is a multi-faceted illness caused by infection due to Borrelia burgdorferi. Acute kidney damage secondary to Lyme disease is well described but less so as a chronic event. The role of Anaplasma spp. and secondary kidney dysfunction is not known. A retrospective cohort study was performed to determine if dogs within a defined Lyme disease and anaplasmosis region with B. burgdorferi or Anaplasma spp. antibodies had an increased risk of chronic kidney disease (CKD). Patient exposure was defined as having a B. burgdorferi or Anaplasma spp. antibody positive result recorded at any point in the available patient history. CKD was defined as concurrent increased symmetric dimethylarginine and creatinine (Cr) for a minimum of 25 days with inappropriate urine specific gravity (USG). Patients were matched using propensity scoring to control for age, region, and breed. Contingency tables were used to compare dogs seropositive and not seropositive to B. burgdorferi and Anaplasma spp. and CKD outcome. For each comparison that was performed, statistical significance was defined by a P-value of <.025. The risk ratio of CKD for patients exposed to B. burgdorferi and Anaplasma spp. were found to be 1.43 (95% confidence interval [CI, 1.27, 1.61], P < .0001) and 1.04, (95% CI [0.87, 1.24], P = .6485), respectively. Results suggest in this cohort no increased risk for developing CKD when exposed to Anaplasma spp. but a significant increase in risk for developing CKD with exposure to B. burgdorferi.

Identifying Spanish Areas at More Risk of Monthly BTV Transmission with a Basic Reproduction Number Approach

Bluetongue virus (BTV) causes a disease that is endemic in Spain and its two major biological vector species, C. imicola and the Obsoletus complex species, differ greatly in their ecology and distribution. Understanding the seasonality of BTV transmission in risk areas is key to improving surveillance and control programs, as well as to better understand the pathogen transmission networks between wildlife and livestock. Here, monthly risk transmission maps were generated using risk categories based on well-known BTV R0 equations and predicted abundances of the two most relevant vectors in Spain. Previously, Culicoides spp. predicted abundances in mainland Spain and the Balearic Islands were obtained using remote sensing data and random forest machine learning algorithm. Risk transmission maps were externally assessed with the estimated date of infection of BTV-1 and BTV-4 historical outbreaks. Our results highlight the differences in risk transmission during April-October, June-August being the period with higher R0 values. Likewise, a natural barrier has been identified between northern and central-southern areas at risk that may hamper BTV spread between them. Our results can be relevant to implement risk-based interventions for the prevention, control and surveillance of BTV and other diseases shared between livestock and wildlife host populations.

Addressing challenges in routine health data reporting in Burkina Faso through Bayesian spatiotemporal prediction of weekly clinical malaria incidence

Sub-Saharan African (SSA) countries’ health systems are often vulnerable to unplanned situations that can hinder their effectiveness in terms of data completeness and disease control. For instance, in Burkina Faso following a workers' strike, comprehensive data on several diseases were unavailable for a long period in 2019. Weather, seasonal-malaria-chemoprevention (SMC), free healthcare, and other contextual data, which are purported to influence malarial disease, provide opportunities to fit models to describe the clinical malaria data and predict the disease spread. Bayesian spatiotemporal modeling was applied to weekly malaria surveillance data from Burkina Faso (2011–2018) while considering the effects of weather, health programs and contextual factors. Then, a prediction was used to deal with weekly missing data for the entire year of 2019, and SMC and free healthcare effects were quantified. Our proposed model accurately predicted weekly clinical malaria incidence (correlation coefficient, r = 0.90). The distribution of clinical malaria incidence was heterogeneous across the country. Overall, national predicted clinical malaria incidence in 2019 (605 per 1000 [95% CrI: 360–990]) increased by 24.7% compared with the year 2015. SMC and the interaction between free healthcare and health facility attendance were associated with a reduction in clinical malaria incidence. Our modeling approach could be a useful tool for strengthening health systems’ resilience by addressing data completeness and could support SSA countries in developing appropriate targets and indicators to facilitate the subnational control effort.

Sentinel surveillance of Lyme disease risk in Canada, 2019: Results from the first year of the Canadian Lyme Sentinel Network (CaLSeN)

Background

Lyme disease is an emerging vector-borne zoonotic disease of increasing public health importance in Canada. As part of its mandate, the Canadian Lyme Disease Research Network (CLyDRN) launched a pan-Canadian sentinel surveillance initiative, the Canadian Lyme Sentinel Network (CaLSeN), in 2019.

Objectives

To create a standardized, national sentinel surveillance network providing a real-time portrait of the evolving environmental risk of Lyme disease in each province.

Methods

A multicriteria decision analysis (MCDA) approach was used in the selection of sentinel regions. Within each sentinel region, a systematic drag sampling protocol was performed in selected sampling sites. Ticks collected during these active surveillance visits were identified to species, and Ixodes spp. ticks were tested for infection with Borrelia burgdorferi, Borrelia miyamotoi, Anaplasma phagocytophilum, Babesia microti and Powassan virus.

Results

In 2019, a total of 567 Ixodes spp. ticks (I. scapularis [n=550]; I. pacificus [n=10]; and I. angustus [n=7]) were collected in seven provinces: British Columbia, Manitoba, Ontario, Québec, New Brunswick, Nova Scotia and Prince Edward Island. The highest mean tick densities (nymphs/100 m²) were found in sentinel regions of Lunenburg (0.45), Montréal (0.43) and Granby (0.38). Overall, the Borrelia burgdorferi prevalence in ticks was 25.2% (0%-45.0%). One I. angustus nymph from British Columbia was positive for Babesia microti, a first for the province. The deer tick lineage of Powassan virus was detected in one adult I. scapularis in Nova Scotia.

Conclusion

CaLSeN provides the first coordinated national active surveillance initiative for tick-borne disease in Canada. Through multidisciplinary collaborations between experts in each province, the pilot year was successful in establishing a baseline for Lyme disease risk across the country, allowing future trends to be detected and studied.

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.

Can the One Health Approach Save Us from the Emergence and Reemergence of Infectious Pathogens in the Era of Climate Change: Implications for Antimicrobial Resistance?

Climate change has become a controversial topic in today’s media despite decades of warnings from climate scientists and has influenced human health significantly with the increasing prevalence of infectious pathogens and contribution to antimicrobial resistance. Elevated temperatures lead to rising sea and carbon dioxide levels, changing environments and interactions between humans and other species. These changes have led to the emergence and reemergence of infectious pathogens that have already developed significant antimicrobial resistance. Although these new infectious pathogens are alarming, we can still reduce the burden of infectious diseases in the era of climate change if we focus on One Health strategies. This approach aims at the simultaneous protection of humans, animals and environment from climate change and antimicrobial impacts. Once these relationships are better understood, these models can be created, but the support of our legislative and health system partnerships are critical to helping with strengthening education and awareness.

Species distribution models for the eastern blacklegged tick, Ixodes scapularis, and the Lyme disease pathogen, Borrelia burgdorferi, in Ontario, Canada

The blacklegged tick, Ixodes scapularis, is established in several regions of Ontario, Canada, and continues to spread into new geographic areas across the province at a rapid rate. This poses a significant public health risk since I. scapularis transmits the Lyme disease-causing bacterium, Borrelia burgdorferi, and other pathogens of potential public health concern. The objective of this study was to develop species distribution models for I. scapularis and B. burgdorferi to predict and compare the potential distributions of the tick vector and the Lyme disease pathogen as well as the ecological factors most important for species establishment. Ticks were collected via tick dragging at 120 sites across southern, central, and eastern Ontario between 2015 and 2018 and tested for tick-borne pathogens. A maximum entropy (Maxent) approach was used to model the potential distributions of I. scapularis and B. burgdorferi. Two independent datasets derived from tick dragging at 25 new sites in 2019 and ticks submitted by the public to local health units between 2015 and 2017 were used to validate the predictive accuracy of the models. The model for I. scapularis showed high suitability for blacklegged ticks in eastern Ontario and some regions along the shorelines of the Great Lakes, and moderate suitability near Algonquin Provincial Park and the Georgian Bay with good predictive accuracy (tick dragging 2019: AUC = 0.898; ticks from public: AUC = 0.727). The model for B. burgdorferi showed a similar predicted distribution but was more constrained to eastern Ontario, particularly between Ottawa and Kingston, and along Lake Ontario, with similarly good predictive accuracy (tick dragging 2019: AUC = 0.958; ticks from public: AUC = 0.863. The ecological variables most important for predicting the distributions of I. scapularis and B. burgdorferi included elevation, distance to deciduous and coniferous forest, proportions of agricultural land, water, and infrastructure, mean summer/spring temperature, and cumulative annual degree days above 0°C. Our study presents a novel application of species distribution modelling for I. scapularis and B. burgdorferi in Ontario, Canada, and provides an up to date projection of their potential distributions for public health knowledge users.

Synergisms in Science: Climate Change and Integrated Pest Management Through the Lens of Communication-2019 Student Debates

Every year, the Student Debates Subcommittee (SDS) of the Student Affairs Committee (SAC) for the annual Entomological Society of America (ESA) meeting organizes the Student Debates. This year, the SAC selected topics based on their synergistic effect or ability to ignite exponential positive change when addressed as a whole. For the 2019 Student Debates, the SAC SDS identified these topic areas for teams to debate and unbiased introduction speakers to address: 1) how to better communicate science to engage the public, particularly in the area of integrated pest management (IPM), 2) the influential impacts of climate change on agriculturally and medically relevant insect pests, and 3) sustainable agriculture techniques that promote the use of IPM to promote food security. Three unbiased introduction speakers gave a foundation for our audience to understand each debate topic, while each of six debate teams provided a strong case to support their stance or perspective on a topic. Debate teams submitted for a competitive spot for the annual ESA Student Debates and trained for the better part of a year to showcase their talents in presenting logical arguments for a particular topic. Both the debate teams and unbiased introduction speakers provided their insight toward a better understanding of the complexities of each topic and established a foundation to delve further into the topics of science advocacy and communication, climate change, and the many facets of integrated pest management.

Circulation of Tick-Borne Spirochetes in Tick and Small Mammal Communities in Santa Barbara County, California, USA

A diversity of Borrelia burgdorferi sensu lato (Johnson, Schmid, Hyde, Steigerwalt & Brenner) (Spirochaetales: Spirochaetaceae) genomospecies, including the Lyme disease agent, Borrelia burgdorferi sensu stricto (s.s.), have been identified in the western United States. However, enzootic transmission of B. burgdorferi s.l. in small mammals and ticks is poorly characterized throughout much of the region. Here we report prevalence of B. burgdorferi s.l. in small mammal and tick communities in the understudied region of southern California. We found B. burgdorferi s.l. in 1.5% of Ixodes species ticks and 3.6% of small mammals. Infection was uncommon (~0.3%) in Ixodes pacificus Cooley and Kohls (Acari: Ixodidae), the primary vector of the Lyme disease agent to humans in western North America, but a diversity of spirochetes-including Borrelia bissettiae, Borrelia californiensis, Borrelia americana, and B. burgdorferi s.s.-were identified circulating in Ixodes species ticks and their small mammal hosts. Infection with B. burgdorferi s.l. is more common in coastal habitats, where a greater diversity of Ixodes species ticks are found feeding on small mammal hosts (four species when compared with only I. pacificus in other sampled habitats). This provides some preliminary evidence that in southern California, wetter coastal areas might be more favorable for enzootic transmission than hotter and drier climates. Infection patterns confirm that human transmission risk of B. burgdorferi s.s. is low in this region. However, given evidence for local maintenance of B. burgdorferi s.l., more studies of enzootic transmission may be warranted, particularly in understudied regions where the tick vector of B. burgdorferi s.s. occurs.

A Retrospective Assessment of Temperature Trends in Northern Europe Reveals a Deep Impact on the Life Cycle of Ixodes ricinus (Acari: Ixodidae)

This study modelled the changes in the development processes of the health-threatening tick Ixodes ricinus in Northern Europe as driven by the trends of temperature (1950–2018). We used the ECA&D dataset to calculate the annual accumulated temperature to obtain the development rates of the oviposition, incubation, larva–nymph, and nymph–adult molts. Annual values were used to ascertain the trend in development rates of each stage. The ecological classification of Northern Europe (LANMAP2) was used to summarize results. The temperature in 1950–2018 clearly increased in the target territory. The development rates of every tested life cycle process were faster along the time series. Faster oviposition and incubation rates resulted in central Sweden, Baltic countries, and parts of Finland. Faster molting rates were observed in the same territories and in large areas of Western Norway. The trend of temperature in the period 1950–2018 shows a consistent inflection point around 1990, demonstrating that the increased annual accumulated temperature has a deeper impact on the life cycle of I. ricinus since approximately 1990. Faster development rates could be part of the processes driving the reported spread of the tick in the target area and should be considered as a serious threat to human health.

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.

PERK-Mediated Unfolded Protein Response Signaling Restricts Replication of the Tick-Borne Flavivirus Langat Virus

The unfolded protein response (UPR) maintains protein-folding homeostasis in the endoplasmic reticulum (ER) and has been implicated as both beneficial and detrimental to flavivirus infection. Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), a sensor of the UPR, is commonly associated with antiviral effects during mosquito-borne flavivirus (MBFV) infection, but its relation to tick-borne flavivirus (TBFV) infection remains largely unexplored. In this study, we identified changes in UPR and autophagic activity during Langat virus (LGTV) infection. LGTV robustly activated UPR and altered autophagic flux. Knockdown of endogenous PERK in human cells resulted in increased LGTV replication, but not that of closely related Powassan virus (POWV). Finally, on examining changes in protein levels of components associated with UPR and autophagy in the absence of PERK, we could show that LGTV-infected cells induced UPR but did not lead to expression of C/EBP homologous protein (CHOP), an important downstream transcription factor of multiple stress pathways. From these data, we hypothesize that LGTV can antagonize other kinases that target eukaryotic initiation factor 2α (eIF2α), but not PERK, implicating PERK as a potential mediator of intrinsic immunity. This effect was not apparent for POWV, a more pathogenic TBFV, suggesting it may be better equipped to mitigate the antiviral effects of PERK.

Ixodes scapularis: Vector to an Increasing Diversity of Human Pathogens in the Upper Midwest

INTRODUCTION

The black-legged tick, Ixodes scapularis (I scapularis), is now recognized as the deadliest tick vector in the United States. The Upper Midwest, particularly Wisconsin and Minnesota, are endemic to a diversity of tick-transmitted infectious diseases. Although Borrelia burgdorferi, the agent of Lyme disease, still accounts for the majority of diagnosed infections, I scapularis is known to transmit other bacterial, viral, and parasitic agents.

OBJECTIVE

To provide an overview of the array of pathogenic microorganisms carried by I scapularis ticks in the Upper Midwest.

METHODS

A literature review was conducted to collect and analyze current information about I scapularis lifestyle, transmission, microorganisms carried by the arthropod vector, and the diseases that occur as a result of infections with these microorganisms in the Upper Midwest.

RESULTS

Diagnosis of co-infection from tick-borne zoonosis in humans has increased over the last 2 decades. Since I scapularis can transmit multiple pathogens, it is clinically important because different diagnostic testing and treatment strategies may need to be implemented for a patient with I scapularis-borne infection(s).

CONCLUSIONS

This review has concentrated on I scapularis-transmitted diseases affecting the Upper Midwest and has explored the ecology of the I scapularis vector and its role in pathogen transmission.

Post-treatment Lyme Disease as a Model for Persistent Symptoms in Lyme Disease

It has long been observed in clinical practice that a subset of patients with Lyme disease report a constellation of symptoms such as fatigue, cognitive difficulties, and musculoskeletal pain, which may last for a significant period of time. These symptoms, which can range from mild to severe, have been reported throughout the literature in both prospective and population-based studies in Lyme disease endemic regions. The etiology of these symptoms is unknown, however several illness-causing mechanisms have been hypothesized, including microbial persistence, host immune dysregulation through inflammatory or secondary autoimmune pathways, or altered neural networks, as in central sensitization. Evaluation and characterization of persistent symptoms in Lyme disease is complicated by potential independent, repeat exposures to B. burgdorferi, as well as the potential for co-morbid diseases with overlapping symptom profiles. Antibody testing for B. burgdorferi is an insensitive measure after treatment, and no other FDA-approved tests currently exist. As such, diagnosis presents a complex challenge for physicians, while the lived experience for patients is one marked by uncertainty and often illness invalidation. Currently, there are no FDA-approved pharmaceutical therapies, and the safety and efficacy of off-label and/or complementary therapies have not been well studied and are not agreed-upon within the medical community. Post-treatment Lyme disease represents a narrow, defined, mechanistically-neutral subset of this larger, more heterogeneous group of patients, and is a useful definition in research settings as an initial subgroup of study. The aim of this paper is to review the current literature on the diagnosis, etiology, risk factors, and treatment of patients with persistent symptoms in the context of Lyme disease. The meaning and relevance of existing patient subgroups will be discussed, as will future research priorities, including the need to develop illness biomarkers, elucidate the biologic mechanisms of disease, and drive improvements in therapeutic options.

Emerging Tick-Borne Diseases

Increases in tick-borne disease prevalence and transmission are important public health issues. Efforts to control these emerging diseases are frustrated by the struggle to control tick populations and to detect and treat infections caused by the pathogens that they transmit. This review covers tick-borne infectious diseases of nonrickettsial bacterial, parasitic, and viral origins. While tick surveillance and tracking inform our understanding of the importance of the spread and ecology of ticks and help identify areas of risk for disease transmission, the vectors are not the focus of this document. Here, we emphasize the most significant pathogens that infect humans as well as the epidemiology, clinical features, diagnosis, and treatment of diseases that they cause. Although detection via molecular or immunological methods has improved, tick-borne diseases continue to remain underdiagnosed, making the scope of the problem difficult to assess. Our current understanding of the incidence of tick-borne diseases is discussed in this review. An awareness of the diseases that can be transmitted by ticks in specific locations is key to detection and selection of appropriate treatment. As tick-transmitted pathogens are discovered and emerge in new geographic regions, our ability to detect, describe, and understand the growing public health threat must also grow to meet the challenge.

First report of Lyme borreliosis leading to cardiac bradydysrhythmia in two cats

Case series summary

Two cats were presented for investigation of bradyarrhythmia detected by their referring veterinarians during routine examination. Both cats had extensive investigations, including haematology, serum biochemistry with electrolytes and thyroxine concentrations, systolic blood pressure measurement, echocardiography, electrocardiography and infectious disease testing. Infectious disease testing included serology for Toxoplasma gondii, Ehrlichia canis, Anaplasma phagocytophilum and Borrelia burgdorferi, and PCR for B burgdorferi antigen in both cats. Case 1 was also assessed by PCR for Bartonella henselae antigen and case 2 was assessed for Dirofilaria immitis by serology. All infectious disease tests, other than for B burgdorferi, were negative. Case 1 was diagnosed with Lyme carditis based on marked bradydysrhythmia, positive B burgdorferi serology, a structurally normal heart and clinical resolution with appropriate treatment with a 4-year follow-up. Case 2 was diagnosed with Lyme carditis based on marked bradydysrhythmia and positive B burgdorferi PCR; however, this cat had structural heart disease that did not resolve with treatment.

Relevance and novel information

This small case series describes two B burgdorferi positive cats presenting with newly diagnosed cardiac abnormalities consistent with those found in humans and dogs with Lyme carditis. Both cats were asymptomatic as perceived by their owners; the arrhythmia was detected by their veterinarians.

Woodchip borders at the forest ecotone as an environmental control measure to reduce questing tick density along recreational trails in Ottawa, Canada

Recent studies have highlighted the occurrence and distribution of Ixodes scapularis ticks infected with Borrelia burgdorferi sensu stricto (s.s.) around the city of Ottawa, Ontario, Canada, and the need for strategies to mitigate the risk of human exposure and infection. We conducted a field study from July to October 2018 to examine the effectiveness of ecotonal woodchip borders as an environmental control method to suppress the density of host-seeking ticks along recreational trails in Ottawa. We used an experimental design with ten 100-m trail replicates randomized to intervention or control groups, and monitored questing tick density at weekly intervals in mid-summer and early fall. We compared questing tick density between woodchip-treated and untreated trails using a mixed-effects Poisson regression model. Of the 138 I. scapularis ticks collected, there were 86 adult and nymphal ticks, 37 (43 %) of which were positive for B. burgdorferi s.s. A total of 58 Haemaphysalis leporispalustris were also collected. Mean combined adult and nymphal I. scapularis density was 1.15 (1.40 standard deviation; SD) per 100 m in the control group compared to 0.28 (0.56 SD) per 100 m in the intervention group, reflecting a 75 % reduction in questing tick density on trail replicates treated with woodchip borders (p < 0.001). An effect of the intervention was observed in both sampling periods. This study indicates that woodchip borders may be an effective strategy to suppress questing tick density along trail margins where recreational trail users are more active, thereby reducing the likelihood of tick encounters.

Predicted Northward Expansion of the Geographic Range of the Tick Vector Amblyomma americanum in North America under Future Climate Conditions

BACKGROUND

The geographic range of the tick Amblyomma americanum, a vector of diseases of public health significance such as ehrlichiosis, has expanded from the southeast of the United States northward during the 20th century. Recently, populations of this tick have been reported to be present close to the Canadian border in Michigan and New York states, but established populations are not known in Canada. Previous research suggests that changing temperature patterns with climate change may influence tick life cycles and permit northward range expansion of ticks in the northern hemisphere.

OBJECTIVES

We aimed to estimate minimal temperature conditions for survival of A. americanum populations at the northern edge of the tick's range and to investigate the possibility of range expansion of A. americanum into northern U.S. states and southern Canada in the coming decades.

METHODS

A simulation model of the tick A. americanum was used, via simulations using climate data from meteorological stations in the United States and Canada, to estimate minimal temperature conditions for survival of A. americanum populations at the northern edge of the tick's range.

RESULTS

The predicted geographic scope of temperature suitability [≥3,285  annual cumulative degree days (DD) >0°C] included most of the central and eastern U.S. states east of longitude 110°W, which is consistent with current surveillance data for the presence of the tick in this region, as well as parts of southern Quebec and Ontario in Canada. Regional climate model output raises the possibility of northward range expansion into all provinces of Canada from Alberta to Newfoundland and Labrador during the coming decades, with the greatest northward range expansion (up to 1,000km by the year 2100) occurring under the greenhouse gas (GHG) emissions of Representative Concentration Pathway (RCP) 8.5. Predicted northward range expansion was reduced by approximately half under the reduced GHG emissions of RCP4.5.

DISCUSSION

Our results raise the possibility of range expansion of A. americanum into northern U.S. states and southern Canada in the coming decades, and conclude that surveillance for this tick, and the diseases it transmits, would be prudent. https://doi.org/10.1289/EHP5668.

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.

The Need for a National Strategy to Address Vector-Borne Disease Threats in the United States

Vector-borne diseases (VBDs) cause significant morbidity and mortality each year in the United States. Over the last 14 yr, over 700,000 cases of diseases carried by ticks, mosquitoes, and fleas have been reported from U.S. states and territories to the Centers for Disease Control and Prevention. The number of reported cases has been increasing annually with two major trends: a steady increase in tick-borne diseases and increasing intermittent outbreaks of mosquito-borne arboviruses. The factors that are driving VBD introduction and emergence vary among diseases but are not likely to disappear, indicating that current trends will continue and probably worsen in the absence of effective prevention and control tools and implementation capacity. There are a number of challenges to preventing VBDs, including the lack of vaccines and effective vector control tools, insecticide resistance, and eroding technical capacities in public health entomology at federal, state, and local levels. For these reasons, a national strategy is needed to address VBD threats and to reverse the alarming trend in morbidity and mortality associated with these diseases.

Estimating the Health-Related Costs of 10 Climate-Sensitive U.S. Events During 2012

Climate change threatens human health, but there remains a lack of evidence on the economic toll of climate-sensitive public health impacts. We characterize human mortality and morbidity costs associated with 10 climate-sensitive case study events spanning 11 US states in 2012: wildfires in Colorado and Washington, ozone air pollution in Nevada, extreme heat in Wisconsin, infectious disease outbreaks of tick-borne Lyme disease in Michigan and mosquito-borne West Nile virus in Texas, extreme weather in Ohio, impacts of Hurricane Sandy in New Jersey and New York, allergenic oak pollen in North Carolina, and harmful algal blooms on the Florida coast. Applying a consistent economic valuation approach to published studies and state estimates, we estimate total health-related costs from 917 deaths, 20,568 hospitalizations, and 17,857 emergency department visits of $10.0 billion in 2018 dollars, with a sensitivity range of $2.7-24.6 billion. Our estimates indicate that the financial burden of deaths, hospitalizations, emergency department visits, and associated medical care is a key dimension of the overall economic impact of climate-sensitive events. We found that mortality costs (i.e., the value of a statistical life) of $8.4 billion exceeded morbidity costs and lost wages ($1.6 billion combined). By better characterizing health damages in economic terms, this work helps to shed light on the burden climate-sensitive events already place on U.S. public health each year. In doing so, we provide a conceptual framework for broader estimation of climate-sensitive health-related costs. The high health-related costs associated with climate-sensitive events highlight the importance of actions to mitigate climate change and adapt to its unavoidable impacts.

Parenting When Children Have Lyme Disease: Fear, Frustration, Advocacy

Increasing numbers of Canadians, including children and adolescents, are being infected with Borrelia burgdorferi and contracting Lyme disease. In the present study, we provided a qualitative analysis of written correspondence produced by 23 parents of children and adolescents with Lyme disease. The goal of this study was to investigate how medical and psychological issues were highlighted by parents describing their family’s Lyme disease experiences. The results suggest a series of four stages in these families where satisfactory treatment had not been obtained over months or years. The experiences of parents evolved from feelings of worry for the child to frustration with the lack of a helpful treatment, to mistrust of physicians’ actions, and, in some case, to a rejection of the conventional health care system as a whole. Improved diagnostic testing and treatment guidelines, as well as family-centered practices of medical care were proposed as important features for improving the experiences of families living with Lyme disease.

Skewed temperature dependence affects range and abundance in a warming world

Population growth metrics such as R₀ are usually asymmetric functions of temperature, with cold-skewed curves arising when the positive effects of a temperature increase outweigh the negative effects, and warm-skewed curves arising in the opposite case. Classically, cold-skewed curves are interpreted as more beneficial to a species under climate warming, because cold-skewness implies increased population growth over a larger proportion of the species's fundamental thermal niche than warm-skewness. However, inference based on the shape of the fitness curve alone, and without considering the synergistic effects of net reproduction, density and dispersal, may yield an incomplete understanding of climate change impacts. We formulate a moving-habitat integrodifference equation model to evaluate how fitness curve skewness affects species' range size and abundance during climate warming. In contrast to classic interpretations, we find that climate warming adversely affects populations with cold-skewed fitness curves, positively affects populations with warm-skewed curves and has relatively little or mixed effects on populations with symmetric curves. Our results highlight the synergistic effects of fitness curve skewness, spatially heterogeneous densities and dispersal in climate change impact analyses, and that the common approach of mapping changes only in R₀ may be misleading.

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.

A framework for adaptive surveillance of emerging tick-borne zoonoses

Significant global ecological changes continue to drive emergence of tick-borne zoonoses around the world. This poses an important threat to both human and animal health, and highlights the need for surveillance systems that are capable of monitoring these complex diseases effectively across different stages of the emergence process. Our objective was to develop an evidence-based framework for surveillance of emerging tick-borne zoonoses. We conducted a realist review to understand the available approaches and major challenges associated with surveillance of emerging tick-borne zoonoses. Lyme disease, with a specific focus on emergence in Canada, was used as a case study to provide real-world context, since the process of disease emergence is ongoing in this country. We synthesize the results to propose a novel framework for adaptive surveillance of emerging tick-borne zoonoses. Goals for each phase of disease emergence are highlighted and approaches are suggested. The framework emphasizes the needs for surveillance systems to be inclusive, standardized, comprehensive and sustainable. We build upon a growing body of infectious disease literature that is advocating for reform to surveillance systems. Although our framework has been developed for tick-borne zoonoses, it is flexible and has the potential to be applied to a variety of other vector-borne and zoonotic diseases.

The effects of multiyear and seasonal weather factors on incidence of Lyme disease and its vector in New York State

BACKGROUND

More frequent extreme weather and warmer weather due to climate change might change the spatiotemporal distributions of vector-borne diseases, including Lyme disease. However, limited studies have examined the associations of Lyme disease and its vectors with weather factors, especially multi-year and multi-weather factors related to vector life cycle.

OBJECTIVES

We investigated the associations between multi-year, unique weather indicators (relevant to tick and host activities) and Lyme disease incidence or documented I. scapularis encounters in New York State (NYS).

METHODS

Using a generalized estimating equation model, we linked Lyme disease and tick (I. scapularis) data, obtained from the NYS Department of Health (NYSDOH) Communicable Disease Surveillance and Tick Identification Service, with weather data. We used a season-specific exposure index by considering days in different seasons with certain temperature and precipitation ranges, summer Palmer Hydrological Drought Index, and fitted linear regression models using generalized estimating equations.

RESULTS

Lyme disease and I. scapularis encounters were modestly correlated (Spearman correlation = 0.60, p-value <0.001). The results indicate that summer Lyme disease cases and tick encounters may increase by 4-10%, per one day in spring with a minimum temperature range between 40 and 50 °F in the year of diagnosis and previous year. A day increase in summer with maximum temperature > 75 °F in the previous year was associated with 2% increase in summer disease counts. Mild winter days were associated with an increase in summer tick encounters.

CONCLUSIONS

Extended spring and summer days and mild winter temperatures appear to increase Lyme disease cases and tick exposure risk in NYS.

N Increased risk of tick-borne diseases with climate and environmental changes

Climate warming and other environmental changes have contributed to the expansion of the range of several tick species into higher latitudes in North America. As temperatures increase in Canada, the environment becomes more suitable for ticks and the season suitable for tick activity lengthens, so tick-borne diseases are likely to become more common in Canada. In addition to Lyme disease, four other tick-borne diseases (TBDs) have started to emerge and are likely to increase: Anaplasmosis; Babesiosis; Powassan virus; and Borrelia miyamotoi disease. Increased temperature increases the survival and activity period of ticks, increases the range of both reservoir and tick hosts (e.g. mice and deer) and increases the duration of the season when people may be exposed to ticks. Other ticks and TBDs may spread into Canada as the climate changes. The public health strategies to mitigate the impact of all TBDs include surveillance to detect current and emerging TBDs, and public health actions to prevent infections by modifying environmental and social-behavioral risk factors through increasing public awareness. Clinical care strategies include patient education, early detection, laboratory testing, and treatment.

N Increased risk of tick-borne diseases with climate and environmental changes

Climate warming and other environmental changes have contributed to the expansion of the range of several tick species into higher latitudes in North America. As temperatures increase in Canada, the environment becomes more suitable for ticks and the season suitable for tick activity lengthens, so tick-borne diseases are likely to become more common in Canada. In addition to Lyme disease, four other tick-borne diseases (TBDs) have started to emerge and are likely to increase: Anaplasmosis; Babesiosis; Powassan virus; and Borrelia miyamotoi disease. Increased temperature increases the survival and activity period of ticks, increases the range of both reservoir and tick hosts (e.g. mice and deer) and increases the duration of the season when people may be exposed to ticks. Other ticks and TBDs may spread into Canada as the climate changes. The public health strategies to mitigate the impact of all TBDs include surveillance to detect current and emerging TBDs, and public health actions to prevent infections by modifying environmental and social-behavioral risk factors through increasing public awareness. Clinical care strategies include patient education, early detection, laboratory testing, and treatment.

Survival and energy use of Ixodes scapularis nymphs throughout their overwintering period

The blacklegged tick (Ixodes scapularis) spends up to 10 months in the soil between feeding as larvae and questing for hosts as nymphs the following year. We tracked the survival and energy use of 4320 engorged larvae evenly divided across 288 microcosms under field conditions from September to July on sites with high (>12 nymphs/150 m2) and low (<1.2 nymphs/150 m2) densities of naturally questing I. scapularis in New York State. Subsets of microcosms were destructively sampled periodically during this period to determine tick survivorship and physiological age. Across all sites tick mortality was low during the winter and increased in the spring and early summer, coincident with increasing energy use. Neither energy use nor mortality differed significantly between sites with high vs low natural tick density, but we did observe a significant positive relationship between soil organic matter content and the survival of I. scapularis during the spring. Our results suggest that the off-host mortality and energy use of I. scapularis nymphs is relatively low in the winter and increases significantly in the spring and early summer.

Searching for clues for eighteen years: Deciphering the ecological determinants of Cryptococcus gattii on Vancouver Island, British Columbia

Cryptococcus gattii emerged on Vancouver Island in 1999 for unknown reasons, causing human and animal fatalities and illness. The apparent emergence of this fungus in another temperate area, this time in the Pacific Northwest, suggests the fungus may have expanded its ecological niche. Yet studies that directly examine the potential roles of climatic and land use changes on C. gattii are still lacking. We aim to summarize the existing global literature on the ecology of C. gattii, with particular focus on the gap in knowledge surrounding the potential effects of climatic and land use changes. We systematically reviewed English peer-reviewed literature on the ecological determinants of C. gattii. We included studies published from January 1970 through June 2016 and identified 56 relevant studies for our review. We identified environmental isolations of C. gattii from 18 countries, spanning 72 separate regions across six continents. Fifty-three tree species were associated with C. gattii, spanning 10 climate classifications and 36 terrestrial ecoregions. No studies directly tested the potential effects of climatic changes (including climatic oscillations and global climate change) on C. gattii, while only one study directly assessed those of land use change. To improve model predictions of current and future distributions of C. gattii, more focus is needed on the potential effects of climatic and land use changes to help decrease the public health risk. The apparent emergence of C. gattii in British Columbia is also an opportunity to explore the factors behind emerging infectious diseases in Canada and elsewhere.

How ticks keep ticking in the adversity of host immune reactions

Ixodid ticks are acknowledged as one of the most important hematophagous arthropods because of their ability in transmitting a variety of tick-borne diseases. Mathematical models have been developed, based on emerging knowledge about tick ecology, pathogen epidemiology and their interface, to understand tick population dynamics and tick-borne diseases spread patterns. However, no serious effort has been made to model and assess the impact of host immunity triggered by tick feeding on the distribution of the tick population according to tick stages and on tick population extinction and persistence. Here, we construct a novel mathematical model taking into account the effect of host immunity status on tick population dynamics, and analyze the long-term behaviours of the model solutions. Two threshold values, [Formula: see text] and [Formula: see text], are introduced to measure the reproduction ratios for the tick-host interaction in the absence and presence of host immunity. We then show that these two thresholds (sometimes under additional conditions) can be used to predict whether the tick population goes extinct ([Formula: see text]) and the tick population grows without bound ([Formula: see text]). We also prove tick permanence (persistence and boundedness of the tick population) and the existence of a tick persistence equilibrium if [Formula: see text]. As the host species adjust their immunity to tick infestation levels, they form for the tick population an environment with a carrying capacity very much like that in logistic growth. Numerical results show that the host immune reactions decrease the size of the tick population at equilibrium and apparently reduce the tick-borne infection risk.

Evaluating the risk for Usutu virus circulation in Europe: comparison of environmental niche models and epidemiological models

Background

Usutu virus (USUV) is a mosquito-borne flavivirus, reported in many countries of Africa and Europe, with an increasing spatial distribution and host range. Recent outbreaks leading to regional declines of European common blackbird (Turdus merula) populations and a rising number of human cases emphasize the need for increased awareness and spatial risk assessment.

Methods

Modelling approaches in ecology and epidemiology differ substantially in their algorithms, potentially resulting in diverging model outputs. Therefore, we implemented a parallel approach incorporating two commonly applied modelling techniques: (1) Maxent, a correlation-based environmental niche model and (2) a mechanistic epidemiological susceptible-exposed-infected-removed (SEIR) model. Across Europe, surveillance data of USUV-positive birds from 2003 to 2016 was acquired to train the environmental niche model and to serve as test cases for the SEIR model. The SEIR model is mainly driven by daily mean temperature and calculates the basic reproduction number R₀. The environmental niche model was run with long-term bio-climatic variables derived from the same source in order to estimate climatic suitability.

Results

Large areas across Europe are currently suitable for USUV transmission. Both models show patterns of high risk for USUV in parts of France, in the Pannonian Basin as well as northern Italy. The environmental niche model depicts the current situation better, but with USUV still being in an invasive stage there is a chance for under-estimation of risk. Areas where transmission occurred are mostly predicted correctly by the SEIR model, but it mostly fails to resolve the temporal dynamics of USUV events. High R₀ values predicted by the SEIR model in areas without evidence for real-life transmission suggest that it may tend towards over-estimation of risk.

Conclusions

The results from our parallel-model approach highlight that relying on a single model for assessing vector-borne disease risk may lead to incomplete conclusions. Utilizing different modelling approaches is thus crucial for risk-assessment of under-studied emerging pathogens like USUV.

Electronic supplementary material

The online version of this article (10.1186/s12942-018-0155-7) contains supplementary material, which is available to authorized users.

A scoping review of Lyme disease research relevant to public health

Lyme disease (LD) is an emerging infectious disease in Canada associated with expansion of the geographic range of the tick vector Ixodes scapularis in eastern and central Canada. A scoping review of published research was prioritized to identify and characterize the scientific evidence concerning key aspects of LD to support public health efforts. Prior to initiation of this review, an expert advisory group was surveyed to solicit insight on priority topics and scope. A pre-tested search strategy implemented in eight databases (updated September 2016) captured relevant research. Pre-tested screening and data characterization forms were completed by two independent reviewers and descriptive analysis was conducted to identify topic areas with solid evidence and knowledge gaps. Of 19,353 records screened, 2,258 relevant articles were included in the review under the following six public health focus areas: a) surveillance/monitoring in North America (n=809); b) evaluation of diagnostic tests (n=736); c) risk factors (n=545); d) public health interventions (n=205); e) public knowledge, attitudes and/or perceptions in North America (n=202); and f) the economic burden of LD or cost-benefit of interventions (n=32). The majority of research investigated Borrelia burgdorferi (n=1,664), humans (n=1,154) and Ixodes scapularis (n=459). Sufficient research was identified for potential systematic reviews in four topic areas: a) accuracy of diagnostic tests; b) risk factors for human illness; c) efficacy of LD intervention strategies; and d) prevalence and/or incidence of LD in humans or B. burgdorferi sensu stricto in vertebrate reservoirs or ticks in North America. Future primary research could focus on closing knowledge gaps, such as the role of less studied vertebrate reservoirs in the transmission cycle. Results of this scoping review can be used to quickly identify and summarize relevant research pertaining to specific questions about LD or B. burgdorferi sensu lato in humans, vertebrate hosts or vectors, providing evidence-informed information within timelines that are conducive for public health decision-making.

Basic reproduction number for the Brazilian Spotted Fever

Brazilian Spotted Fever (BSF) is an emerging and lethal disease in South America which basic reproduction number (R₀) is unknown. Calculating R₀ for this disease is crucial to design control interventions and prevent human deaths. BSF endemic areas are related to the presence of capybaras Hydrochoerus hydrochaeris, amplifier hosts of Rickettsia rickettsii and primary hosts of the tick Amblyomma sculptum, main vector of the agent in this area. Because of the complexity of its dynamics, we calculated R₀ for the BSF system by constructing a next-generation matrix considering different categories of vectors and hosts. Each matrix element was considered as the expected number of infected individuals of one category produced by a single infected individual of a second category. We used field and experimental data to parameterize the next-generation matrix and obtain the final calculation (R₀ ≈ 1.7). We demonstrated the low impact of the matrix elements corresponding to the transovarial transmission and the transmission from infected larvae in the maintenance of R. rickettsii. Sensitivity and elasticity analyzes were performed to quantify the perturbations of each matrix element in R₀. We noted that the elements equivalent to the number of infected attached nymphs produced by an infected capybara, and the number of infected capybaras produced by an infected attached nymph or adult are the major contributors to changes in R₀. Our results provide insights into the strategic design of preventive interventions in BSF endemic areas.

Abiotic and habitat drivers of tick vector abundance, diversity, phenology and human encounter risk in southern California

The distribution, abundance and seasonal activity of vector species, such as ticks and mosquitoes, are key determinants of vector-borne disease risk, and are strongly influenced by abiotic and habitat conditions. Despite the numerous species of tick vectors in the heavily populated North American West Coast, all but Ixodes pacificus, the primary vector of the Lyme disease spirochete, is poorly characterized with regard to seasonal activity patterns and fine scale drivers of distribution and abundance, particularly in heavily populated regions of southern California. This lack of knowledge inhibits both scientific understanding and public health efforts to minimize vector exposure and risk of pathogen transmission to humans. Here we address this gap by characterizing the abiotic and habitat drivers of the distribution, abundance, and diversity of the vector tick community using fine scale temporal surveys over two seasons (2014 and 2015) across coastal and inland regions of Santa Barbara County, CA. We also characterize patterns of seasonal activity of the more common vector species to understand seasonality in risk of vector exposure, and specifically focus on human encounter risk using standardized tick drags as our method of collection. Leveraging plot-level habitat and abiotic variables in partial least squares regression analysis, we find the seven different vector species collected in this study have divergent drivers of activity and abundance. For example, I. pacificus is strongly associated with dense forest habitats and cool and moist microclimates, while Dermacentor occidentalis and Dermacentor variabilis, competent vectors of Rocky Mountain Spotted Fever, were found to be more tolerant of higher average temperatures and more open habitats. These results suggest that I. pacificus may be expected to experience reductions in geographic distribution and seasonal activity under projected land cover and climate change in coastal southern California, while D. occidentalis may experience more limited effects. We discuss implications for changing tick-borne disease risk associated with pathogens transmitted by Ixodes as well as Dermacentor species ticks in the western US, and contrast these predictions with eastern North America.

Evidence for an effect of landscape connectivity on Borrelia burgdorferi sensu stricto dispersion in a zone of range expansion

In North America, different strains of the Lyme disease-causing bacterium Borrelia burgdorferi sensu stricto cluster into phylogenetic groups that are associated with different levels of pathogenicity and, for some, specific rodent reservoir hosts. Here we explore whether landscape connectivity, by impacting host dispersal, influences B. burgdorferi s.s. spread patterns. This question is central to modelling spatial patterns of the spread of Lyme disease risk in the zone of northward range-expansion of B. burgdorferi s.s. in southeastern Canada where the study was conducted. We used multi-locus sequence typing (MLST) to characterise B. burgdorferi s.s. in positive ticks collected at 13 sites in southern Quebec, Canada during the early stages of B. burgdorferi s.s. invasion. We used mixed effects logistic regression to investigate whether landscape connectivity (probability of connectivity; PC) affected the probability that samples collected at different sites were of the same strain (MLST sequence type: ST). PC was calculated from a habitat map based on high spatial resolution (15 m) Landsat 8 imagery to identify woodland habitat that are preferred by rodent hosts of B. burgdorferi s.s. There was a significant positive association between the likelihood that two samples were of the same ST and PC, when PC values were grouped into three categories of low, medium and high. When analysing data for individual STs, samples at different sites were significantly more likely to be the same when PC was higher for the rodent-associated ST1. These findings support the hypothesis that dispersion trajectories of B. burgdorferi s.s. in general, and some rodent-associated strains in particular, are at least partly determined by landscape connectivity. This may suggest that dispersion of B. burgdorferi s.s. is more common by terrestrial mammal hosts (which would likely disperse according to landscape connectivity) than by birds, the dispersal of which is likely less constrained by landscape. This study suggests that accounting for landscape connectivity may improve model-based predictions of spatial spread patterns of B. burgdorferi s.s. The findings are consistent with possible past dispersal patterns of B. burgdorferi s.s. as determined by phylogeographic studies.

Ticks and Tick-Borne Infections: Complex Ecology, Agents, and Host Interactions

Ticks transmit the most diverse array of infectious agents of any arthropod vector. Both ticks and the microbes they transmit are recognized as significant threats to human and veterinary public health. This article examines the potential impacts of climate change on the distribution of ticks and the infections they transmit; the emergence of novel tick-borne pathogens, increasing geographic range and incidence of tick-borne infections; and advances in the characterization of tick saliva mediated modulation of host defenses and the implications of those interactions for transmission, establishment, and control of tick infestation and tick-borne infectious agents.

Limiting global-mean temperature increase to 1.5-2 °C could reduce the incidence and spatial spread of dengue fever in Latin America

This study is a multigeneral circulation model, multiscenario modeling exercise developed to quantify the dengue-related health benefits of limiting global warming to 1.5–2.0 °C above preindustrial levels in Latin America and the Caribbean. We estimate the impact of future climate change and population growth on the additional number of dengue cases and provide insights about the regions and periods most likely affected by changes in the length of the transmission season. Here, we show that future climate change may amplify dengue transmission and that significant impacts could be avoided by constraining global warming to 1.5 °C above preindustrial levels. Our work could be a starting point for future risk assessments incorporating other important drivers of disease such as urbanization and international traveling.

The Paris Climate Agreement aims to hold global-mean temperature well below 2 °C and to pursue efforts to limit it to 1.5 °C above preindustrial levels. While it is recognized that there are benefits for human health in limiting global warming to 1.5 °C, the magnitude with which those societal benefits will be accrued remains unquantified. Crucial to public health preparedness and response is the understanding and quantification of such impacts at different levels of warming. Using dengue in Latin America as a study case, a climate-driven dengue generalized additive mixed model was developed to predict global warming impacts using five different global circulation models, all scaled to represent multiple global-mean temperature assumptions. We show that policies to limit global warming to 2 °C could reduce dengue cases by about 2.8 (0.8–7.4) million cases per year by the end of the century compared with a no-policy scenario that warms by 3.7 °C. Limiting warming further to 1.5 °C produces an additional drop in cases of about 0.5 (0.2–1.1) million per year. Furthermore, we found that by limiting global warming we can limit the expansion of the disease toward areas where incidence is currently low. We anticipate our study to be a starting point for more comprehensive studies incorporating socioeconomic scenarios and how they may further impact dengue incidence. Our results demonstrate that although future climate change may amplify dengue transmission in the region, impacts may be avoided by constraining the level of warming.

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.

Changes in extreme events and the potential impacts on human health

Extreme weather and climate-related events affect human health by causing death, injury, and illness, as well as having large socioeconomic impacts. Climate change has caused changes in extreme event frequency, intensity, and geographic distribution, and will continue to be a driver for change in the future. Some of these events include heat waves, droughts, wildfires, dust storms, flooding rains, coastal flooding, storm surges, and hurricanes. The pathways connecting extreme events to health outcomes and economic losses can be diverse and complex. The difficulty in predicting these relationships comes from the local societal and environmental factors that affect disease burden. More information is needed about the impacts of climate change on public health and economies to effectively plan for and adapt to climate change. This paper describes some of the ways extreme events are changing and provides examples of the potential impacts on human health and infrastructure. It also identifies key research gaps to be addressed to improve the resilience of public health to extreme events in the future.

IMPLICATIONS

Extreme weather and climate events affect human health by causing death, injury, and illness, as well as having large socioeconomic impacts. Climate change has caused changes in extreme event frequency, intensity, and geographic distribution, and will continue to be a driver for change in the future. Some of these events include heat waves, droughts, wildfires, flooding rains, coastal flooding, surges, and hurricanes. The pathways connecting extreme events to health outcomes and economic losses can be diverse and complex. The difficulty in predicting these relationships comes from the local societal and environmental factors that affect disease burden.

Emerging infectious diseases: prediction and detection

Emerging infectious diseases (EIDs), including West Nile virus, severe acute respiratory syndrome (SARS) and Lyme disease, have had a direct effect within Canada, while many more EIDs such as Zika, chikungunya and Ebola are a threat to Canadians while travelling. Over 75% of EIDs affecting humans are, or were originally, zoonoses (infectious diseases transmitted from animals to humans). There are two main ways by which infectious diseases can emerge: by changes in their geographical ranges and by adaptive emergence, a genetic change in a microorganism that results in it becoming capable of invading a new niche, often by jumping to a new host species such as humans. Diseases can appear to emerge simply because we become capable of detecting and diagnosing them. Management of EID events is a key role of public health globally and a considerable challenge for clinical care. Increasingly, emphasis is being placed on predicting EID occurrence to "get ahead of the curve" - that is, allowing health systems to be poised to respond to them, and public health to be ready to prevent them. Predictive models estimate where and when EIDs may occur and the levels of risk they pose. Evaluation of the internal and external drivers that trigger emergence events is increasingly considered in predicting EID events. Currently, global changes are driving increasing occurrence of EIDs, but our capacity to prevent and deal with them is also increasing. Web-based scanning and analysis methods are increasingly allowing us to detect EID outbreaks, modern genomics and bioinformatics are increasing our ability to identify their genetic and geographical origins, while developments in geomatics and earth observation will enable more real-time tracking of outbreaks. EIDs will, however, remain a key, global public health challenge in a globalized world where demographic, climatic, and other environmental changes are altering the interactions between hosts and pathogen in ways that increase spillover from animals to humans and global spread.

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.

Reproduction numbers of infectious disease models

This primer article focuses on the basic reproduction number, ℛ 0 , for infectious diseases, and other reproduction numbers related to ℛ 0 that are useful in guiding control strategies. Beginning with a simple population model, the concept is developed for a threshold value of ℛ 0 determining whether or not the disease dies out. The next generation matrix method of calculating ℛ 0 in a compartmental model is described and illustrated. To address control strategies, type and target reproduction numbers are defined, as well as sensitivity and elasticity indices. These theoretical ideas are then applied to models that are formulated for West Nile virus in birds (a vector-borne disease), cholera in humans (a disease with two transmission pathways), anthrax in animals (a disease that can be spread by dead carcasses and spores), and Zika in humans (spread by mosquitoes and sexual contacts). Some parameter values from literature data are used to illustrate the results. Finally, references for other ways to calculate ℛ 0 are given. These are useful for more complicated models that, for example, take account of variations in environmental fluctuation or stochasticity.

A Risk Model for the Lyme Disease Vector Ixodes scapularis (Acari: Ixodidae) in the Prairie Provinces of Canada

Lyme disease is emerging in Canada due to geographic range expansion of the tick vector Ixodes scapularis Say. Recent areas of emergence include parts of the southeastern Canadian Prairie region. We developed a map of potential risk areas for future I. scapularis establishment in the Canadian Prairie Provinces. Six I. scapularis risk algorithms were developed using different formulations of three indices for environmental suitability: temperature using annual cumulative degree-days > 0 °C (DD > 0 °C; obtained from Moderate Resolution Imaging Spectroradiometer satellite data as an index of conditions that allow I. scapularis to complete its life cycle), habitat as a combined geolayer of forest cover and agricultural land use, and rainfall. The relative performance of these risk algorithms was assessed using receiver-operating characteristic (ROC) area under the curve (AUC) analysis with data on presence-absence of I. scapularis obtained from recent field surveillance in the Prairie Provinces accumulated from a number of sources. The ROC AUC values for the risk algorithms were significantly different (P < 0.01). The algorithm with six categories of DD > 0 °C, habitat as a simple dichotomous variable of presence or absence of forest, and normalized rainfall had the highest AUC of 0.74, representing "fair to good" performance of the risk algorithm. This algorithm had good (>80%) sensitivity in predicting positive I. scapularis surveillance sites, but low (50%) specificity as expected in this region where not all environmentally suitable habitats are expected to be occupied. Further prospective studies are needed to validate and perhaps improve the risk algorithm.