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'.
1. A population model for the tick Ixodes ricinus, the most significant vector of pathogens in Europe, is used to explore the relative impact of changes in climate, host density and acaricide-treated ...hosts on tick abundance and seasonality. 2. A rise in temperature of the sort witnessed since 1989 speeds up the inter-stadial development of ticks, thereby reducing the cumulative effect of constant daily mortality rates and potentially raising population levels. The predicted earlier onset of tick-questing activity in the spring, due to stage-specific temperature thresholds, could increase contact between ticks and humans during recreational visits to the countryside in spring holidays. These tick population effects vary geographically with background climate. 3. The significant increase in deer abundance across Europe, including the UK, in recent decades is predicted to drive tick population increases, the effect varying with the initial density of hosts. In areas only recently colonized by deer, tick numbers are predicted to rise dramatically (given suitable climatic conditions). Where host densities are already high, however, further increases may reduce numbers of questing ticks; unfed ticks leave the questing population more rapidly, even though the overall tick population (and therefore pathogen transmission potential) increases. 4. Culling high-density deer populations as a control measure could, therefore, initially cause an apparent increase in questing ticks, with the predicted long-term population trajectory depending on the severity of the cull. 5. Conversely, the further addition of large hosts (e.g. sheep) would effectively reduce the number of questing ticks and therefore the risk to humans. If such sheep were treated with acaricide, tick populations are predicted to decrease rapidly, to an extent that depends on the relative abundance of wild (untreated) and treated hosts. Tick control in designated areas may be achieved by using sheep in this way as 'lethal mops', as used to occur in the past when sheep were regularly dipped. 6. Synthesis and applications. Both abiotic and biotic environmental changes witnessed recently could have contributed to apparent increases in tick populations, especially where these environmental factors were limiting in the past. The release of additional hosts treated with long-lasting acaricide is potentially an effective control strategy.
1. The sheep tick Ixodes ricinus is the most multicompetent vector in Europe, which is responsible for significant diseases of humans and livestock throughout the northern hemisphere. Modelling the ...tick's complex seasonal dynamics, upon which pathogen transmission potential depends, underpins the analysis of tick-borne disease risk and potential tick control. 2. We use laboratory- and field-derived empirical data to construct a population model for I. ricinus. The model is a substantially modified stage-classified Leslie matrix and includes functions for temperature-dependent development, density-dependent mortality and saturation deficit—meditated probability of questing. 3. The model was fitted to field data from three UK sites and successfully simulated seasonal patterns at a fourth site. After modification of a single parameter, the model also replicated divergent seasonal patterns in central Spain, but any biological factors underlying this geographical heterogeneity have not yet been identified. The model's applicability to wide geographical areas is thus constrained, but in ways that highlight gaps in our knowledge of tick biology. 4. Sensitivity analysis indicated that the model was generally robust, particularly to changes in density-independent mortality values, but was most sensitive to changes in parameters related to density-dependent mortality. 5. Synthesis and applications. Vector population models allow investigation into the effects of individual environmental factors on population dynamics in ways not easily possible by experimental manipulation of in situ populations. Our model can be used to evaluate public health risk, tick management strategies and potential effects of future environmental change.
The geographic patterns of transmission opportunities of vector-borne zoonoses are determined by a complex interplay between the migration patterns of the host and the vector. Here we examine the ...impact of host migration on the spread of a tick-borne zoonotic disease, using Lyme Borreliosis (LB) spirochaetal species in Europe. We demonstrate that the migration of the LB species is dependent on and limited by the migration of their respective hosts. We note that populations of Borrelia spp. associated with birds (Borrelia garinii and B. valaisiana) show limited geographic structuring between countries compared with those associated with small mammals (Borrelia afzelii), and we argue that this can be explained by higher rates of migration in avian hosts. We also show the presence of B. afzelii strains in England and, through the use of the multi-locus sequence analysis scheme, reveal that the strains are highly structured. This pattern in English sites is very different from that observed at the continental sites, and we propose that these may be recent introductions.
Conservation takes place within social-ecological systems, and many conservation interventions aim to influence human behaviour in order to push these systems towards sustainability. Predictive ...models of human behaviour are potentially powerful tools to support these interventions. This is particularly true if the models can link the attributes and behaviour of individuals with the dynamics of the social and environmental systems within which they operate. Here we explore this potential by showing how combining two modelling approaches (social network analysis, SNA, and agent-based modelling, ABM) could lead to more robust insights into a particular type of conservation intervention. We use our simple model, which simulates knowledge of ranger patrols through a hunting community and is based on empirical data from a Cambodian protected area, to highlight the complex, context-dependent nature of outcomes of information-sharing interventions, depending both on the configuration of the network and the attributes of the agents. We conclude by reflecting that both SNA and ABM, and many other modelling tools, are still too compartmentalized in application, either in ecology or social science, despite the strong methodological and conceptual parallels between their uses in different disciplines. Even a greater sharing of methods between disciplines is insufficient, however; given the impact of conservation on both the social and ecological aspects of systems (and vice versa), a fully integrated approach is needed, combining both the modelling approaches and the disciplinary insights of ecology and social science. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.
Dengue virus (DENV) infection is prevalent across tropical regions and may cause severe disease. Early diagnosis may improve supportive care. We prospectively assessed the Standard Diagnostics ...(Korea) BIOLINE Dengue Duo DENV rapid diagnostic test (RDT) to NS1 antigen and anti-DENV IgM (NS1 and IgM) in children in Cambodia, with the aim of improving the diagnosis of DENV infection.
We enrolled children admitted to hospital with non-localised febrile illnesses during the 5-month DENV transmission season. Clinical and laboratory variables, and DENV RDT results were recorded at admission. Children had blood culture and serological and molecular tests for common local pathogens, including reference laboratory DENV NS1 antigen and IgM assays. 337 children were admitted with non-localised febrile illness over 5 months. 71 (21%) had DENV infection (reference assay positive). Sensitivity was 58%, and specificity 85% for RDT NS1 and IgM combined. Conditional inference framework analysis showed the additional value of platelet and white cell counts for diagnosis of DENV infection. Variables associated with diagnosis of DENV infection were not associated with critical care admission (70 children, 21%) or mortality (19 children, 6%). Known causes of mortality were melioidosis (4), other sepsis (5), and malignancy (1). 22 (27%) children with a positive DENV RDT had a treatable other infection.
The DENV RDT had low sensitivity for the diagnosis of DENV infection. The high co-prevalence of infections in our cohort indicates the need for a broad microbiological assessment of non-localised febrile illness in these children.
Detecting deterrence from patrol data Dobson, Andrew D. M.; Milner‐Gulland, E. J.; Beale, Colin M. ...
Conservation biology,
June 2019, Letnik:
33, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The threat posed to protected areas by the illegal killing of wildlife is countered principally by ranger patrols that aim to detect and deter potential offenders. Deterring poaching is a fundamental ...conservation objective, but its achievement is difficult to identify, especially when the prime source of information comes in the form of the patrols’ own records, which inevitably contain biases. The most common metric of deterrence is a plot of illegal activities detected per unit of patrol effort (CPUE) against patrol effort (CPUE‐E). We devised a simple, mechanistic model of law breaking and law enforcement in which we simulated deterrence alongside exogenous changes in the frequency of offences under different temporal patterns of enforcement effort. The CPUE‐E plots were not reliable indicators of deterrence. However, plots of change in CPUE over change in effort (ΔCPUE‐ΔE) reliably identified deterrence, regardless of the temporal distribution of effort or any exogenous change in illegal activity levels as long as the time lag between patrol effort and subsequent behavioral change among offenders was approximately known. The ΔCPUE‐ΔE plots offered a robust, simple metric for monitoring patrol effectiveness; were no more conceptually complicated than the basic CPUE‐E plots; and required no specialist knowledge or software to produce. Our findings demonstrate the need to account for temporal autocorrelation in patrol data and to consider appropriate (and poaching‐activity‐specific) intervals for aggregation. They also reveal important gaps in understanding of deterrence in this context, especially the mechanisms by which it occurs. In practical applications, we recommend the use of ΔCPUE‐ΔE plots in preference to other basic metrics and advise that deterrence should be suspected only if there is a clear negative slope. Distinct types of illegal activity should not be grouped together for analysis, especially if the signs of their occurrence have different persistence times in the environment.
Detección de la Disuasión a Partir de Datos de Patrullaje
Resumen
La amenaza que representa la caza ilegal de fauna para las áreas protegidas está contrarrestada principalmente por las patrullas de guardias que buscan detectar y disuadir a los delincuentes potenciales. La disuasión de la caza furtiva es un objetivo fundamental de la conservación, pero es difícil identificar cuándo se logra, especialmente cuando la fuente principal de información proviene de los propios registros de las patrullas, que inevitablemente contiene sesgos. La medida más común de la disuasión es una parcela de actividades ilegales detectadas por unidad de esfuerzo de patrullaje (CPUE, en inglés) contra el esfuerzo de patrullaje (CPUE‐E, en inglés). Diseñamos un modelo simple y mecánico del rompimiento y aplicación de la ley en el cual simulamos la disuasión junto con cambios exógenos en la frecuencia de ofensas bajo diferentes patrones temporales del esfuerzo de aplicación. Las parcelas de CPUE‐E no fueron indicadores confiables de la disuasión. Sin embargo, las parcelas de cambio de CPUE sobre cambio en el esfuerzo (ΔCPUE‐ΔE) identificaron con seguridad la disuasión sin importar la distribución temporal del esfuerzo o cualquier cambio exógeno en los niveles de actividad ilegal siempre y cuando el retraso en el tiempo entre el esfuerzo de patrullaje y el cambio en comportamiento subsecuente entre los delincuentes se conocía con cierta aproximación. Las parcelas de ΔCPUE‐ΔE ofrecieron una medida simple y sólida para el monitoreo de la efectividad del patrullaje; no fueron más complicadas conceptualmente que las parcelas básicas de CPUE‐E; y no requirieron de conocimiento de especialistas o algún software para producir. Nuestros hallazgos demuestran la necesidad de dar cuenta de la autocorrelación temporal en los datos de patrullaje y de considerar intervalos apropiados (y específicos a la actividad de caza furtiva) para su agregación. Nuestros hallazgos también revelan vacíos importantes en el entendimiento de la disuasión en este contexto, especialmente para los mecanismos mediante los cuales ocurre. En las aplicaciones prácticas recomendamos el uso de parcelas de ΔCPUE‐ΔE por encima de otras medidas básicas y recomendamos que se sospeche de la disuasión sólo si existe una clara pendiente negativa. No se deben agrupar diferentes tipos de actividades ilegales para su análisis, especialmente si las señales de su ocurrencia tienen diferentes momentos de persistencia en el ambiente.
摘要
野生动物的非法捕杀对保护地构成的威胁主要被以发现并阻止潜在罪犯为目标的巡逻队员的巡逻活动来应对。制止偷猎是一项基本的保护目标, 但目标是否实现难以判断, 特别是信息主要来自巡逻队自身记录的时候, 这样就不可避免地存在偏差。判断巡逻威慑力最常见的标准是将每单位巡逻量发现的非法活动 (CPUE) 与巡逻量进行作图 (CPUE‐E) 。我们设计了一个简单机械的违法与执法模型, 模拟了在不同时间格局的执法工作下威慑力与外在因素导致的犯罪频率变化。结果显示, CPUE‐E 图不能可靠地评估巡逻的威慑力。但是对 CPUE 在巡逻量变化下的变化 (ΔCPUE‐ΔE) 作图可以很好地确定威慑力, 且不受巡逻时间分布或非法活动强度外因变化的影响, 只要能大致确定巡逻工作和随后罪犯行为变化的时间差即可。 ΔCPUE‐ΔE 图提供了监测巡逻有效性简单稳健的指标, 它没有比基础的 CPUE‐E 图更难以理解, 也不需要其它专业知识或软件进行绘制。我们的发现指出, 需要考虑巡逻数据的时间自相关性, 并选择适当的 (及偷猎行为特定的) 汇总时间间隔。结果还揭示了目前对威慑力的认识存在不足, 特别是它产生的机制。在实际应用中, 我们建议优先使用 ΔCPUE‐ΔE 图, 且只有斜率明显为负时才应怀疑威慑力的作用。不同类型的非法活动不应该归为一类进行分析, 特别是当它们在环境中留下的痕迹存在时间不一样长的时候。翻译: 胡怡思; 审校: 聂永刚
Article impact statement: Deterrent effects of conservation law enforcement may be robustly assessed by applying relatively simple metrics to ranger patrol data.
BACKGROUND: The risk posed by ticks as vectors of disease is typically assessed by blanket-drag sampling of host-seeking individuals. Comparisons of peak abundance between plots – either in order to ...establish their relative risk or to identify environmental correlates – are often carried out by sampling on one or two occasions during the period of assumed peak tick activity. METHODS: This paper simulates this practice by ‘re-sampling’ from model datasets derived from an empirical field study. Re-sample dates for each plot are guided by either the previous year’s peak at the plot, or the previous year’s peak at a similar, nearby plot. Results from single, double and three-weekly sampling regimes are compared. RESULTS: Sampling on single dates within a two-month window of assumed peak activity has the potential to introduce profound errors; sampling on two dates (double sampling) offers greater precision, but three-weekly sampling is the least biased. CONCLUSIONS: The common practice of sampling for the abundance of host-seeking ticks on single dates in each plot-year should be strenuously avoided; it is recommended that field acarologists employ regular sampling throughout the year at intervals no greater than three weeks, for a variety of epidemiological studies.
BACKGROUND: Numerical responses of ticks to changes in densities of their hosts can be complex and apparently unpredictable. Manipulations even of deterministic models can produce counter-intuitive ...results, including tick populations that either rise or fall under increasing host densities, depending on initial conditions. METHODS: In this paper I use an established simulation model to demonstrate a wide range of numerical responses to different scenarios of host changes, and to examine the basic mechanisms that drive them. RESULTS: The rate and direction of change of host densities affects the extent to which questing tick numbers reflect those of their hosts. Numerical responses differ profoundly between dynamic tick-host systems and those allowed to reach equilibrium. CONCLUSIONS: The key to understanding tick-host dynamics is to understand the difference between ‘real’ and ‘visible’ tick populations. An appreciation of the implications of this difference – and of the conditions that influence it - will benefit the effective interpretation of field data.
Hunting is a primary driver of biodiversity loss across South-east Asia. Within Cambodia, the use of wire snares to capture wildlife is a severe threat in protected areas but there have been few ...studies of the behaviour of hunters from local communities. Here, we combine the unmatched count technique with direct questioning to estimate the prevalence of hunting behaviours and wildlife consumption amongst 705 households living within Keo Seima Wildlife Sanctuary, Cambodia. We assessed respondents’ knowledge of rules, and their perceptions of patrols responsible for enforcing rules. Estimates of hunting behaviour were variable: results from the unmatched count technique were inconclusive, and direct questioning revealed 9% of households hunted, and 20% set snares around farms to prevent wildlife eating crops. Hunting with domestic dogs was the method most commonly used to catch wildlife (87% of households owned dogs). Wild meat was consumed by 84% of households, and was most frequently bought or caught, but also gifted. We detected a high awareness of conservation rules, but low awareness of punishments and penalties, with wildlife depletion, rather than the risk of being caught by patrols, causing the greatest reduction in hunting. Our findings demonstrate the challenges associated with reliably estimating rule-breaking behaviour and highlight the need to incorporate careful triangulation into study design.
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