Detecting deterrence from patrol data.

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.

Epidemiological Implications of Host Biodiversity and Vector Biology: Key Insights from Simple Models.

Models used to investigate the relationship between biodiversity change and vector-borne disease risk often do not explicitly include the vector; they instead rely on a frequency-dependent transmission function to represent vector dynamics. However, differences between classes of vector (e.g., ticks and insects) can cause discrepancies in epidemiological responses to environmental change. Using a pair of disease models (mosquito- and tick-borne), we simulated substitutive and additive biodiversity change (where noncompetent hosts replaced or were added to competent hosts, respectively), while considering different relationships between vector and host densities. We found important differences between classes of vector, including an increased likelihood of amplified disease risk under additive biodiversity change in mosquito models, driven by higher vector biting rates. We also draw attention to more general phenomena, such as a negative relationship between initial infection prevalence in vectors and likelihood of dilution, and the potential for a rise in density of infected vectors to occur simultaneously with a decline in proportion of infected hosts. This has important implications; the density of infected vectors is the most valid metric for primarily zoonotic infections, while the proportion of infected hosts is more relevant for infections where humans are a primary host.

Host migration impacts on the phylogeography of Lyme Borreliosis spirochaete species in Europe.

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.

Integrating models of human behaviour between the individual and population levels to inform conservation interventions.

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'.

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'.

Rapid diagnostic tests for dengue virus infection in febrile Cambodian children: diagnostic accuracy and incorporation into diagnostic algorithms.

BACKGROUND: 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. METHODOLOGY AND PRINCIPAL FINDINGS: 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. CONCLUSIONS: 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.

History and complexity in tick-host dynamics: discrepancies between 'real' and 'visible' tick populations.

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.

Ticks in the wrong boxes: assessing error in blanket-drag studies due to occasional sampling.

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.

Tick (Ixodes ricinus) abundance and seasonality at recreational sites in the UK: hazards in relation to fine-scale habitat types revealed by complementary sampling methods.

The seasonal risk to humans of picking up Ixodes ricinus ticks in different habitats at 3 recreational sites in the UK was assessed. A comprehensive range of vegetation types was sampled at 3-weekly intervals for 2 years, using standard blanket-dragging complemented by woollen leggings and square 'heel flags'. Ticks were found in all vegetation types sampled, including short grass close to car parks, but highest densities were consistently found in plots with trees present. Blankets picked up the greatest number of ticks, but heel flags provided important complementary counts of the immature stages in bracken plots; they showed clearly that the decline in tick numbers on blankets in early summer was due to the seasonal growth of vegetation that lifted the blanket clear of the typical questing height, but in reality ticks remained abundant through the summer. Leggings picked up only 11% of the total nymphs and 22% of total adults counted, but this still represented a significant hazard to humans. These results should prompt a greater awareness of the fine-scale distribution of this species in relation to human activities that determines the most likely zones of contact between humans and ticks. Risk communication may then be designed accordingly.

Frameworks for risk communication and disease management: the case of Lyme disease and countryside users.

Management of zoonotic disease is necessary if countryside users are to gain benefit rather than suffer harm from their activities, and to avoid disproportionate reaction to novel threats. We introduce a conceptual framework based on the pressure-state-response model with five broad responses to disease incidence. Influencing public behaviour is one response and requires risk communication based on an integration of knowledge about the disease with an understanding of how publics respond to precautionary advice. A second framework emphasizes how risk communication involves more than information provision and should address dimensions including points-of-intervention over time, place and audience. The frameworks are developed by reference to tick-borne Lyme borreliosis (also known as Lyme disease), for which informed precautionary behaviour is particularly relevant. Interventions to influence behaviour can be directed by knowledge of spatial and temporal variation of tick abundance, what constitutes risky behaviour, how people respond to information of varying content, and an understanding of the social practices related to countryside use. The frameworks clarify the response options and help identify who is responsible for risk communication. These aspects are not consistently understood, and may result in an underestimation of the role of land-based organizations in facilitating appropriate precautionary behaviour.