Effects of conservation management of landscapes and vertebrate communities on Lyme borreliosis risk in the United Kingdom

Land system governance shapes tick-related public and animal health risks

Land cover and land use have established effects on hazard and exposure to vector-borne diseases. While our understanding of the proximate and distant causes and consequences of land use decisions has evolved, the focus on the proximate effects of landscape on disease ecology remains dominant. We argue that land use governance, viewed through a land system lens, affects tick-borne disease risk. Governance affects land use trajectories and potentially shapes landscapes favourable to ticks or increases contact with ticks by structuring human-land interactions. We illustrate the role of land use legacies, trade-offs in land-use decisions, and social inequities in access to land resources, information and decision-making, with three cases: Kyasanur Forest disease in India, Lyme disease in the Outer Hebrides (Scotland), and tick acaricide resistance in cattle in Ecuador. Land use governance is key to managing the risk of tick-borne diseases, by affecting the hazard and exposure. We propose that land use governance should consider unintended consequences on infectious disease risk.

Recreational hazard: Vegetation and host habitat use correlate with changes in tick-borne disease hazard at infrastructure within forest stands

Studies on density and pathogen prevalence of Ixodes ricinus indicate that vegetation and local host community drive much of their variation between green spaces. Contrarily, micro-geographic variation is understudied, although its understanding could reduce disease risk. We studied the density of infectious nymphal Ixodes sp. ("DIN", proxy for disease hazard), density of questing nymphs ("DON") and nymphal infection prevalence ("NIP") near recreational forest infrastructure. Drag sampling within forest stands and at adjacent benches and trails was combined with vegetation surveys, camera trapping hosts and pathogen screening of ticks. We analysed Borrelia burgdorferi s.l. and its genospecies, with complementary analyses on Rickettsia sp., Anaplasma phagocytophilum, Neoehrlichia mikurensis and Borrelia miyamotoi. DIN was highest in forest interior and at trails enclosed by forest. Lower disease hazard was observed at benches and trails at forest edges. This infrastructure effect can be attributed to variation in vegetation characteristics and the habitat use of tick hosts, specifically roe deer, rodents and songbirds. DON is the main driver of DIN at micro-geographic scale and negatively affected by infrastructure and forest edges. A positive association with vegetation cover in understorey and canopy was observed, as were positive trends for local rodent and songbird abundance. NIP of different pathogens was affected by different drivers. Lower B. burgdorferi s.l. prevalence in the interior of forest stands, driven by its most prevalent genospecies B. afzelii, points towards higher density of uninfected hosts there. B. afzelii was positively associated with understorey containing tall species and with high canopy cover, whereas local bird community composition predicts B. garinii prevalence. A positive effect of songbird abundance and a negative effect of pigeons were observed. Our findings support amplification and inhibition mechanisms within forest stands and highlight that the effect of established drivers of DIN may differ based on the considered spatial scale.

Predicting the current and future risk of ticks on livestock farms in Britain using random forest models

The most abundant tick species in northern Europe, Ixodes ricinus, transmits a range of pathogens that cause disease in livestock. As I. ricinus distribution is influenced by climate, tick-borne disease risk is expected to change in the future. The aims of this work were to build a spatial model to predict current and future risk of ticks on livestock farms across Britain. Variables relating both to tick hazard and livestock exposure were included, to capture a niche which may be missed by broader scale models. A random forest machine learning model was used due to its ability to cope with correlated variables and interactions. Data on tick presence and absence on sheep and cattle farms was obtained from a retrospective questionnaire survey of 926 farmers. The ROC of the final model was 0.80. The model outputs matched observed patterns of tick distribution, with areas of highest tick risk in southwest and northwest England, Wales, and west Scotland. Overall, the probability of tick presence on livestock farms was predicted to increase by 5-7 % across Britain under future climate scenarios. The predicted increase is greater at higher altitudes and latitudes, further increasing the risk of tick-borne disease on farms in these areas.

Meta-analysis: A useful tool to assess infection prevalence and disease ecology of Borrelia burgdorferi sensu lato in nymphal ticks in North-Western Europe with recommendations for a standardised approach to future studies

Lyme borreliosis is a vector-borne disease of concern in Europe. While neuroborreliosis data are reportable at EU level, it can nevertheless be difficult to make comparisons of disease risk between neighbouring countries. This study used proportion meta-analyses to compare environmental markers of disease risk between woodland sites in two countries in North-Western Europe (Ireland, Scotland). 73 site-visits from 12 publications were analysed, resulting in a significantly higher pooled nymphal infection prevalence (NIP) in Ireland (8.2% (95% CI: 5.9–11.4%)) than Scotland (1.7%(95% CI 1.1–2.5%)). All other analysed parameters of disease risk were also higher in Ireland than Scotland. Subgroup-meta-analyses and meta-regressions were used to assess the influence of environmental variables on NIP. NIP increased significantly with increasing woodland size in Ireland, but not Scotland, which may be accounted for by Ireland's highly fragmented landscape.

Assuming the application of strict inclusion/exclusion criteria and control of variables, proportion meta-analysis can provide useful insights in disease ecology, as it allows for the achievement of high study powers incorporating samples collected across multiple sites, which is otherwise often a prohibitively difficult and resource-heavy feat in environmental studies in disease ecology. A standardised approach to data collection is recommended to achieve more robust meta-analyses in future in conjunction with additional research on environmental factors affecting Lyme borreliosis risk in Europe, particularly pertaining to the impact of host species on NIP.

Habitat suitability map of <em>Ixodes ricinus</em> tick in France using multi-criteria analysis

The tick Ixodes ricinus is widely distributed across Europe and is responsible for the transmission of several pathogens to humans and animals. In this study, we used a knowledge-based method to map variations in habitat suitability for I. ricinus ticks throughout continental France and Corsica. The multi-criteria decision analysis (MCDA) integrated four major biotic and abiotic factors known to influence tick populations: climate, land cover, altitude and the density of wild ungulates. For each factor, habitat suitability index (HSI) values were attributed to different locations based on knowledge regarding its impact on tick populations. For the MCDA, two methods of factor combination were tested, additive and multiplicative, both which were evaluated at the spatial scales of departments and local municipalities. The resulting habitat suitability maps (resolution=100x100 m) revealed that conditions are suitable for I. ricinus over most of France and Corsica. Particularly suitable habitats were located in central, north-eastern and south-western France, while less-suitable habitats were found in the Mediterranean and mountainous regions. To validate the approach, the HSI scores were compared to field data of I. ricinus nymph abundance. Regardless of scale, the correlation between abundance indicator and HSI score was stronger for the additive than for the multiplicative approach. Overall, this study demonstrates the value of MCDA for estimating habitat suitability maps for I. ricinus abundance, which could be especially useful in highlighting areas of the tick's distribution where preventive measures should be prioritised.

One Health Approach to Tick and Tick-Borne Disease Surveillance in the United Kingdom

Where ticks are found, tick-borne diseases can present a threat to human and animal health. The aetiology of many of these important diseases, including Lyme disease, bovine babesiosis, tick-borne fever and louping ill, have been known for decades whilst others have only recently been documented in the United Kingdom (UK). Further threats such as the importation of exotic ticks through human activity or bird migration, combined with changes to either the habitat or climate could increase the risk of tick-borne disease persistence and transmission. Prevention of tick-borne diseases for the human population and animals (both livestock and companion) is dependent on a thorough understanding of where and when pathogen transmission occurs. This information can only be gained through surveillance that seeks to identify where tick populations are distributed, which pathogens are present within those populations, and the periods of the year when ticks are active. To achieve this, a variety of approaches can be applied to enhance knowledge utilising a diverse range of stakeholders (public health professionals and veterinarians through to citizen scientists). Without this information, the application of mitigation strategies to reduce pathogen transmission and impact is compromised and the ability to monitor the effects of climate change or landscape modification on the risk of tick-borne disease is more challenging. However, as with many public and animal health interventions, there needs to be a cost-benefit assessment on the most appropriate intervention applied. This review will assess the challenges of tick-borne diseases in the UK and argue for a cross-disciplinary approach to their surveillance and control.

The evolving story of Borrelia burgdorferi sensu lato transmission in Europe

Beside mosquitoes, ticks are well-known vectors of different human pathogens. In the Northern Hemisphere, Lyme borreliosis (Eurasia, LB) or Lyme disease (North America, LD) is the most commonly occurring vector-borne infectious disease caused by bacteria of the genus Borrelia which are transmitted by hard ticks of the genus Ixodes. The reported incidence of LB in Europe is about 22.6 cases per 100,000 inhabitants annually with a broad range depending on the geographical area analyzed. However, the epidemiological data are largely incomplete, because LB is not notifiable in all European countries. Furthermore, not only differ reporting procedures between countries, there is also variation in case definitions and diagnostic procedures. Lyme borreliosis is caused by several species of the Borrelia (B.) burgdorferi sensu lato (s.l.) complex which are maintained in complex networks including ixodid ticks and different reservoir hosts. Vector and host influence each other and are affected by multiple factors including climate that have a major impact on their habitats and ecology. To classify factors that influence the risk of transmission of B. burgdorferi s.l. to their different vertebrate hosts as well as to humans, we briefly summarize the current knowledge about the pathogens including their astonishing ability to overcome various host immune responses, regarding the main vector in Europe Ixodes ricinus, and the disease caused by borreliae. The research shows, that a higher standardization of case definition, diagnostic procedures, and standardized, long-term surveillance systems across Europe is necessary to improve clinical and epidemiological data.

The Impact of Deforestation, Urbanization, and Changing Land Use Patterns on the Ecology of Mosquito and Tick-Borne Diseases in Central America

Central America is a unique geographical region that connects North and South America, enclosed by the Caribbean Sea to the East, and the Pacific Ocean to the West. This region, encompassing Belize, Costa Rica, Guatemala, El Salvador, Honduras, Panama, and Nicaragua, is highly vulnerable to the emergence or resurgence of mosquito-borne and tick-borne diseases due to a combination of key ecological and socioeconomic determinants acting together, often in a synergistic fashion. Of particular interest are the effects of land use changes, such as deforestation-driven urbanization and forest degradation, on the incidence and prevalence of these diseases, which are not well understood. In recent years, parts of Central America have experienced social and economic improvements; however, the region still faces major challenges in developing effective strategies and significant investments in public health infrastructure to prevent and control these diseases. In this article, we review the current knowledge and potential impacts of deforestation, urbanization, and other land use changes on mosquito-borne and tick-borne disease transmission in Central America and how these anthropogenic drivers could affect the risk for disease emergence and resurgence in the region. These issues are addressed in the context of other interconnected environmental and social challenges.

Population connectivity in voles (Microtus sp.) as a gauge for tall grass prairie restoration in midwestern North America

Ecological restoration can promote biodiversity conservation in anthropogenically fragmented habitats, but effectiveness of these management efforts need to be statistically validated to determine ’success.’ One such approach is to gauge the extent of recolonization as a measure of landscape permeability and, in turn, population connectivity. In this context, we estimated dispersal and population connectivity in prairie vole (Microtus ochrogaster; N = 231) and meadow vole (M. pennsylvanicus; N = 83) within five tall-grass prairie restoration sites embedded within the agricultural matrix of midwestern North America. We predicted that vole dispersal would be constrained by the extent of agricultural land surrounding restored habitat patches, spatially isolating vole populations and resulting in significant genetic structure. We first employed genetic assignment tests based on 15 microsatellite DNA loci to validate field-derived species-designations, then tested reclassified samples with multivariate and Bayesian clustering to assay for spatial and temporal genetic structure. Population connectivity was further evaluated by calculating pairwise F_ST, then potential demographic effects explored by computing migration rates, effective population size (N_e), and average relatedness (r). Genetic species assignments reclassified 25% of initial field identifications (N = 11 M. ochrogaster; N = 67 M. pennsylvanicus). In M. ochrogaster population connectivity was high across the study area, reflected in little to no spatial or temporal genetic structure. In M. pennsylvanicus genetic structure was detected, but relatedness estimates identified it as kin-clustering instead, underscoring social behavior among populations rather than spatial isolation as the cause. Estimates of N_e and r were stable across years, reflecting high dispersal and demographic resilience. Combined, these metrics suggest the agricultural matrix is highly permeable for voles and does not impede dispersal. High connectivity observed confirms that the restored landscape is productive and permeable for specific management targets such as voles and also demonstrates population genetic assays as a tool to statistically evaluate effectiveness of conservation initiatives.

Borrelia burgdorferi Sensu Lato in Questing and Engorged Ticks from Different Habitat Types in Southern Germany

Borrelia burgdorferi sensu lato (s.l.) causes the most common tick-borne infection in Europe, with Germany being amongst the countries with the highest incidences in humans. This study aimed at (1) comparing infection rates of B. burgdorferi s.l. in questing Ixodes ricinus ticks from different habitat types in Southern Germany, (2) analysing genospecies distribution by habitat type, and (3) testing tissue and ticks from hosts for B. burgdorferi s.l. Questing ticks from urban, pasture, and natural habitats together with feeding ticks from cattle (pasture) and ticks and tissue samples from wild boars and roe deer (natural site) were tested by PCR and RFLP for species differentiation. B. burgdorferi s.l. was found in 29.8% questing adults and 15% nymphs. Prevalence was lower at the urban sites with occurrence of roe deer than where these were absent. Borrelia burgdorferi s.l. DNA was found in 4.8% ticks from roe deer, 6.3% from wild boar, and 7.8% from cattle. Six genospecies were identified in unfed ticks: Borrelia afzelii (48.6%), Borrelia burgdorferi sensu stricto (16%), Borrelia garinii (13.2%), Borrelia valaisiana (7.5%), Borrelia spielmanii (6.2%), and Borrelia bavariensis (0.9%). This study shows high infection levels and a great diversity of Borrelia in questing ticks. The presence of roe deer seems to reduce B. burgdorferi s.l. infection rates in tick populations.

A Mini-Review of Ixodes Ticks Climate Sensitive Infection Dispersion Risk in the Nordic Region

Climate change in the Nordic countries is projected to lead to both wetter and warmer seasons. This, in combination with associated vegetation changes and increased animal migration, increases the potential incidence of tick-borne diseases (TBD) where already occurring, and emergence in new places. At the same time, vegetation and animal management influence tick habitat and transmission risks. In this paper, we review the literature on Ixodes ricinus, the primary vector for TBD. Current and projected distribution changes and associated disease transmission risks are related to climate constraints and climate change, and this risk is discussed in the specific context of reindeer management. Our results indicate that climatic limitations for vectors and hosts, and environmental and societal/institutional conditions will have a significant role in determining the spreading of climate-sensitive infections (CSIs) under a changing climate. Management emerges as an important regulatory "tool" for tick and/or risk for disease transfer. In particular, shrub encroachment, and pasture and animal management, are important. The results underscore the need to take a seasonal view of TBD risks, such as (1) grazing and migratory (host) animal presence, (2) tick (vector) activity, (3) climate and vegetation, and (4) land and animal management, which all have seasonal cycles that may or may not coincide with different consequences of climate change on CSI migration. We conclude that risk management must be coordinated across the regions, and with other land-use management plans related to climate mitigation or food production to understand and address the changes in CSI risks.

Emerging zoonotic diseases originating in mammals: a systematic review of effects of anthropogenic land-use change

Zoonotic pathogens and parasites that are transmitted from vertebrates to humans are a major public health risk with high associated global economic costs. The spread of these pathogens and risk of transmission accelerate with recent anthropogenic land-use changes (LUC) such as deforestation, urbanisation, and agricultural intensification, factors that are expected to increase in the future due to human population expansion and increasing demand for resources.We systematically review the literature on anthropogenic LUC and zoonotic diseases, highlighting the most prominent mammalian reservoirs and pathogens, and identifying avenues for future research.The majority of studies were global reviews that did not focus on specific taxa. South America and Asia were the most-studied regions, while the most-studied LUC was urbanisation. Livestock were studied more within the context of agricultural intensification, carnivores with urbanisation and helminths, bats with deforestation and viruses, and primates with habitat fragmentation and protozoa.Research into specific animal reservoirs has improved our understanding of how the spread of zoonotic diseases is affected by LUC. The behaviour of hosts can be altered when their habitats are changed, impacting the pathogens they carry and the probability of disease spreading to humans. Understanding this has enabled the identification of factors that alter the risk of emergence (such as virulence, pathogen diversity, and ease of transmission). Yet, many pathogens and impacts of LUC other than urbanisation have been understudied.Predicting how zoonotic diseases emerge and spread in response to anthropogenic LUC requires more empirical and data synthesis studies that link host ecology and responses with pathogen ecology and disease spread. The link between anthropogenic impacts on the natural environment and the recent COVID-19 pandemic highlights the urgent need to understand how anthropogenic LUC affects the risk of spillover to humans and spread of zoonotic diseases originating in mammals.

Occurrence of Borrelia and Borreliella species in Ixodes ricinus collected from roe deer in northwestern Spain

Ixodes ricinus, comprising the predominant tick species in Europe, can transmit important human pathogens, including Borreliella spp., the causal agent of Lyme borreliosis. One hundred and seventy five roe deer hunted in two areas (plateau and mountain) of Galicia (northwest Spain) were examined for the presence of ticks; all roe deer were infested by I. ricinus. Nymphs (n = 1000), males (n = 1449) and females (n = 1000) of I. ricinus were analysed in pools of up to 10 ticks to detect both Borreliella and Borrelia DNA. The average number of I. ricinus per roe deer was similar in both areas, regardless of the life stage; although the percentage of Borreliella and Borrelia positive pools was higher in ticks collected from roe deer hunted in the plateau area, no significant differences were detected. Sequence analysis at the flagellin gene allowed the identification of four Borreliella species (Borreliella afzelii, Borreliella garinii, Borreliella lusitaniae and Borreliella valaisiana) and Borrelia miyamotoi in adult males; only B. valaisiana and B. miyamotoi were detected in nymphs and all females were negative. All Borreliella and Borrelia species found in roe deer were previously identified in questing I. ricinus collected in the same study area, although the prevalence was lower in the present study. The analysis of male I. ricinus ticks collected from roe deer gives a good estimation of Borreliella diversity in questing ticks.

Making Vector-Borne Disease Surveillance Work: New Opportunities From the SDG Perspectives

Surveillance of vector-borne diseases (VBDs) exemplifies a One Health approach, which entails coordinated, collaborative, multidisciplinary, and cross-sectoral approaches to address potential or existing health risks originating at the animal-human-ecosystem interface. However, at the intervention stage of the surveillance system, it is sometimes difficult or even impossible to act. The human dimension of VBD control makes them wicked problems requiring an interdisciplinary systems approach beyond the One Health domain. Here, we make a case that the agenda of the UN Sustainable Development Goals (SDGs) can offer new opportunities to address these issues. The health of the population is a concern to us all and is more or less related to all 17 SDGs. The SDGs can provide a common language by which the interests of various stakeholders can be matched and the challenges that society faces identified, studied, and alleviated. To illustrate, the control and prevention of two VBDs, dengue and Lyme borreliosis, were selected and related to specific SDGs. Further, we use the framework proposed by the International Council of Science to: (1) show synergies and trade-offs between the various SDGs; and (2) present SDG 3 to identify policy that can be related to prevention. Engaging in an integrated approach will confront stakeholders with various viewpoints and through these oppositions, innovation can be nurtured. By adhering to the SDG agenda, we present policy advice including new opportunities for vector-borne disease control to reach its own health goals, while simultaneously supporting other sustainable development goals.

Can Protected Areas Mitigate Lyme Disease Risk in Fennoscandia?

This Forum article synthesizes the current evidence on the links between predator-prey interactions, protected areas and spatial variations in Lyme disease risk in Fennoscandia. I suggest key research directions to better understand the role of protected areas in promoting the persistence of diverse predator guilds. Conserving predators could help reducing host populations and Lyme disease risk in northern Europe. There is an urgent need to find possible win-win solutions for biodiversity conservation and human health in ecosystems facing rapid global environmental change.

Emerging and threatening vector-borne zoonoses in the world and in Europe: a brief update

Climatic changes, landscape management, massive human, animal and commodity transportation represent important factors which are contributing to the spread of zoonotic diseases. The environmental and socioeconomic factors affecting the incidence of vector-borne zoonoses and possibilities for the reduction of disease impacts are discussed in the article. The most important zoonoses with expanding area of incidence and/or increasing occurrence are summarized, with special emphasis on the European region. While some diseases and their respective pathogens are indigenous to Europe (e.g. Lyme disease), others have been introduced to Europe from tropical areas (e.g. chikungunya or dengue fever). These emerging diseases may represent a serious threat in near future and better understanding of their spreading mechanisms, pathogenesis and consequent treatment is very important.

Role of mustelids in the life-cycle of ixodid ticks and transmission cycles of four tick-borne pathogens

BACKGROUND

Elucidating which wildlife species significantly contribute to the maintenance of Ixodes ricinus populations and the enzootic cycles of the pathogens they transmit is imperative in understanding the driving forces behind the emergence of tick-borne diseases. Here, we aimed to quantify the relative contribution of four mustelid species in the life-cycles of I. ricinus and Borrelia burgdorferi (sensu lato) in forested areas and to investigate their role in the transmission of other tick-borne pathogens. Road-killed badgers, pine martens, stone martens and polecats were collected in Belgium and the Netherlands. Their organs and feeding ticks were tested for the presence of tick-borne pathogens.

RESULTS

Ixodes hexagonus and I. ricinus were found on half of the screened animals (n = 637). Pine martens had the highest I. ricinus burden, whereas polecats had the highest I. hexagonus burden. We detected DNA from B. burgdorferi (s.l.) and Anaplasma phagocytophilum in organs of all four mustelid species (n = 789), and Neoehrlichia mikurensis DNA was detected in all species, except badgers. DNA from B. miyamotoi was not detected in any of the investigated mustelids. From the 15 larvae of I. ricinus feeding on pine martens (n = 44), only one was positive for B. miyamotoi DNA, and all tested negative for B. burgdorferi (s.l.), N. mikurensis and A. phagocytophilum. The two feeding larvae from the investigated polecats (n = 364) and stone martens (n = 39) were negative for all four pathogens. The infection rate of N. mikurensis was higher in feeding nymphs collected from mustelids compared to questing nymphs, but not for B. burgdorferi (s.l.), B. miyamotoi or A. phagocytophilum.

CONCLUSIONS

Although all stages of I. ricinus can be found on badgers, polecats, pine and stone martens, their relative contribution to the life-cycle of I. ricinus in forested areas is less than 1%. Consequently, the relative contribution of mustelids to the enzootic cycles of I. ricinus-borne pathogens is negligible, despite the presence of these pathogens in organs and feeding ticks. Interestingly, all four mustelid species carried all stages of I. hexagonus, potentially maintaining enzootic cycles of this tick species apart from the cycle involving hedgehogs as main host species.

Assessment of the Public Health Threats Posed by Vector-Borne Disease in the United Kingdom (UK)

In recent years, the known distribution of vector-borne diseases in Europe has changed, with much new information also available now on the status of vectors in the United Kingdom (UK). For example, in 2016, the UK reported their first detection of the non-native mosquito Aedes albopictus, which is a known vector for dengue and chikungunya virus. In 2010, Culex modestus, a principal mosquito vector for West Nile virus was detected in large numbers in the Thames estuary. For tick-borne diseases, data on the changing distribution of the Lyme borreliosis tick vector, Ixodes ricinus, has recently been published, at a time when there has been an increase in the numbers of reported human cases of Lyme disease. This paper brings together the latest surveillance data and pertinent research on vector-borne disease in the UK, and its relevance to public health. It highlights the need for continued vector surveillance systems to monitor our native mosquito and tick fauna, as well as the need to expand surveillance for invasive species. It illustrates the importance of maintaining surveillance capacity that is sufficient to ensure accurate and timely disease risk assessment to help mitigate the UK's changing emerging infectious disease risks, especially in a time of climatic and environmental change and increasing global connectivity.

Arthropods and associated pathogens from native and introduced rodents in Northeastern Italy

Introduced Siberian chipmunks Eutamias sibiricus have been reported to be important reservoirs for human Lyme disease, as they may host high numbers of hard ticks carrying Borrelia spp. and other pathogens. In the present study, we assessed the prevalence of Borrelia spp. and other pathogenic bacteria in ectoparasite arthropod species infesting Siberian chipmunks and coexisting native small rodents. Small rodents were trapped with Sherman traps in Veneto (NE Italy), where the largest Italian populations of chipmunks occur. A total of 14 individual ticks were found on 223 rodents, with 6 more ticks obtained from stored dead chipmunks from the same study area. Ectoparasites were screened for pathogens by molecular analyses including species-specific PCR amplifications. Rickettsia monacensis, Borrelia lusitaniae, and Anaplasma platys were present in the parasites of both native rodents and introduced chipmunks. The present findings suggest a role for the invasive species E. sibiricus in the maintenance of the Ixodes ricinus life cycle, which may result in the modification of the transmission dynamics of tick-borne pathogens. Moreover, the presence of Rickettsia in urban populations of chipmunks may represent a serious risk for human health and should be investigated further.

Ixodes ricinus parasitism of birds increases at higher winter temperatures

Increasing winter temperatures are expected to cause seasonal activity of Ixodes ricinus ticks to extend further into the winter. We caught birds during winter months (November to February) at a site in the west of Scotland over a period of 24 years (1993-1994 to 2016-2017) to quantify numbers of attached I. ricinus and to relate these to monthly mean temperature. No adult ticks were found on any of the 21,731 bird captures, but 946 larvae and nymphs were found, with ticks present in all winter months, on 16 different species of bird hosts. All ticks identified to species were I. ricinus. I. ricinus are now active throughout the year in this area providing temperature permits. No I. ricinus were present in seven out of eight months when the mean temperature was below 3.5º C. Numbers of I. ricinus attached to birds increased rapidly with mean monthly temperatures above 7º C. Winter temperatures in Scotland have been above the long-term average in most years in the last two decades, and this is likely to increase risk of tick-borne disease.

Null expectations for disease dynamics in shrinking habitat: dilution or amplification?

As biodiversity declines with anthropogenic land-use change, it is increasingly important to understand how changing biodiversity affects infectious disease risk. The dilution effect hypothesis, which points to decreases in biodiversity as critical to an increase in infection risk, has received considerable attention due to the allure of a win-win scenario for conservation and human well-being. Yet some empirical data suggest that the dilution effect is not a generalizable phenomenon. We explore the response of pathogen transmission dynamics to changes in biodiversity that are driven by habitat loss using an allometrically scaled multi-host model. With this model, we show that declining habitat, and thus declining biodiversity, can lead to either increasing or decreasing infectious-disease risk, measured as endemic prevalence. Whether larger habitats, and thus greater biodiversity, lead to a decrease (dilution effect) or increase (amplification effect) in infection prevalence depends upon the pathogen transmission mode and how host competence scales with body size. Dilution effects were detected for most frequency-transmitted pathogens and amplification effects were detected for density-dependent pathogens. Amplification effects were also observed over a particular range of habitat loss in frequency-dependent pathogens when we assumed that host competence was greatest in large-bodied species. By contrast, only amplification effects were observed for density-dependent pathogens; host competency only affected the magnitude of the effect. These models can be used to guide future empirical studies of biodiversity-disease relationships across gradients of habitat loss. The type of transmission, the relationship between host competence and community assembly, the identity of hosts contributing to transmission, and how transmission scales with area are essential factors to consider when elucidating the mechanisms driving disease risk in shrinking habitat.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Lyme disease ecology in a changing world: consensus, uncertainty and critical gaps for improving control

Lyme disease is the most common tick-borne disease in temperate regions of North America, Europe and Asia, and the number of reported cases has increased in many regions as landscapes have been altered. Although there has been extensive work on the ecology and epidemiology of this disease in both Europe and North America, substantial uncertainty exists about fundamental aspects that determine spatial and temporal variation in both disease risk and human incidence, which hamper effective and efficient prevention and control. Here we describe areas of consensus that can be built on, identify areas of uncertainty and outline research needed to fill these gaps to facilitate predictive models of disease risk and the development of novel disease control strategies. Key areas of uncertainty include: (i) the precise influence of deer abundance on tick abundance, (ii) how tick populations are regulated, (iii) assembly of host communities and tick-feeding patterns across different habitats, (iv) reservoir competence of host species, and (v) pathogenicity for humans of different genotypes of Borrelia burgdorferi Filling these knowledge gaps will improve Lyme disease prevention and control and provide general insights into the drivers and dynamics of this emblematic multi-host-vector-borne zoonotic disease.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Conservation, development and the management of infectious disease: avian influenza in China, 2004-2012

There is growing evidence that wildlife conservation measures have mixed effects on the emergence and spread of zoonotic disease. Wildlife conservation has been found to have both positive (dilution) and negative (contagion) effects. In the case of avian influenza H5N1 in China, the focus has been on negative effects. Lakes and wetlands attracting migrating waterfowl have been argued to be disease hotspots. We consider the implications of waterfowl conservation for H5N1 infections in both poultry and humans between 2004 and 2012. We model both environmental and economic risk factors. Environmental risk factors comprise the conditions that structure interaction between wild and domesticated birds. Economic risk factors comprise the cost of disease, biosecurity measures and disease risk mitigation. We find that H5N1 outbreaks in poultry populations are indeed sensitive to the existence of wild-domesticated bird mixing zones, but not in the way we would expect from the literature. We find that risk is decreasing in protected migratory bird habitat. Since the number of human cases is increasing in the number of poultry outbreaks, as expected, the implication is that the protection of wetlands important for migratory birds offers unexpected human health benefits.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.

Ticks and the city - are there any differences between city parks and natural forests in terms of tick abundance and prevalence of spirochaetes?

BACKGROUND

Ixodes ricinus ticks are commonly encountered in either natural or urban areas, contributing to Lyme disease agents Borreliella [(Borrelia burgdorferi (sensu lato)] spp. and Borrelia miyamotoi enzootic cycles in cities. It is an actual problem whether urbanization affects pathogen circulation and therefore risk of infection. The aim of the study was to evaluate main tick-borne disease risk factors in natural, endemic areas of north-east (NE) Poland (Białowieża) and urban areas of central Poland (Warsaw), measuring tick abundance/density, prevalence of infection with spirochaetes and diversity of these pathogens in spring-early summer and late summer-autumn periods between 2012 and 2015.

METHODS

Questing I. ricinus ticks were collected from three urban sites in Warsaw, central Poland and three natural sites in Białowieża, NE Poland. A total of 2993 ticks were analyzed for the presence of Borreliella spp. and/or Borrelia miyamotoi DNA by PCR. Tick abundance was analyzed by General Linear Models (GLM). Prevalence and distribution of spirochaetes was analyzed by Maximum Likelihood techniques based on log-linear analysis of contingency tables (HILOGLINEAR). Species typing and molecular phylogenetic analysis based on the sequenced flaB marker were carried out.

RESULTS

Overall 4617 I. ricinus ticks were collected (2258 nymphs and 2359 adults). We report well established population of ticks in urban areas (10.1 ± 0.9 ticks/100 m²), as in endemic natural areas with higher mean tick abundance (16.5 ± 1.5 ticks/100 m²). Tick densities were the highest in spring-early summer in both types of areas. We observed no effect of the type of area on Borreliella spp. and B. miyamotoi presence in ticks, resulting in similar prevalence of spirochaetes in urban and natural areas [10.9% (95% CI: 9.7-12.2%) vs 12.4% (95% CI: 10.1-15.1%), respectively]. Prevalence of spirochaetes was significantly higher in the summer-autumn period than in the spring-early summer [15.0% (95% CI: 12.8-17.5%) vs 10.4% (95% CI: 9.2-11.6%), respectively]. We have detected six species of bacteria present in both types of areas, with different frequencies: dominance of B. afzelii (69.3%) in urban and B. garinii (48.1%) in natural areas. Although we observed higher tick densities in forests than in maintained parks, the prevalence of spirochaetes was significantly higher in the latter [9.8% (95% CI: 8.6-11.0%) vs 17.5% (95% CI: 14.4-20.5%)].

CONCLUSIONS

Surprisingly, a similar risk of infection with Borreliella spp. and/or B. miyamotoi was discovered in highly- and low-transformed areas. We suggest that the awareness of presence of these disease agents in cities should be raised.

Does the impact of biodiversity differ between emerging and endemic pathogens? The need to separate the concepts of hazard and risk

Biodiversity is of critical value to human societies, but recent evidence that biodiversity may mitigate infectious-disease risk has sparked controversy among researchers. The majority of work on this topic has focused on direct assessments of the relationship between biodiversity and endemic-pathogen prevalence, without disentangling intervening mechanisms; thus study outcomes often differ, fuelling more debate. Here, we suggest two critical changes to the approach researchers take to understanding relationships between infectious disease, both endemic and emerging, and biodiversity that may help clarify sources of controversy. First, the distinct concepts of hazards versus risks need to be separated to determine how biodiversity and its drivers may act differently on each. This distinction is particularly important since it illustrates that disease emergence drivers in humans could be quite different to the general relationship between biodiversity and transmission of endemic pathogens. Second, the interactive relationship among biodiversity, anthropogenic change and zoonotic disease risk, including both direct and indirect effects, needs to be recognized and accounted for. By carefully disentangling these interactions between humans' activities and pathogen circulation in wildlife, we suggest that conservation efforts could mitigate disease risks and hazards in novel ways that complement more typical disease control efforts.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.