Infectious diseases of humans, wildlife, and domesticated species are increasing worldwide, driving the need to understand the mechanisms that shape outbreaks. Simultaneously, human activities are drastically reducing biodiversity. These concurrent patterns have prompted repeated suggestions that biodiversity and disease are linked. For example, the dilution effect hypothesis posits that these patterns are causally related; diverse host communities inhibit the spread of parasites via several mechanisms, such as by regulating populations of susceptible hosts or interfering with parasite transmission. However, the generality of the dilution effect hypothesis remains controversial, especially for zoonotic diseases of humans. Here we provide broad evidence that host diversity inhibits parasite abundance using a metaanalysis of 202 effect sizes on 61 parasite species. The magnitude of these effects was independent of host density, study design, and type and specialization of parasites, indicating that dilution was robust across all ecological contexts examined. However, the magnitude of dilution was more closely related to the frequency, rather than density, of focal host species. Importantly, observational studies overwhelmingly documented dilution effects, and there was also significant evidence for dilution effects of zoonotic parasites of humans. Thus, dilution effects occur commonly in nature, and they may modulate human disease risk. A second analysis identified similar effects of diversity in plant-herbivore systems. Thus, although there can be exceptions, our results indicate that biodiversity generally decreases parasitism and herbivory. Consequently, anthropogenic declines in biodiversity could increase human and wildlife diseases and decrease crop and forest production.H uman activities are dramatically reducing biodiversity (1), and the frequency and severity of infectious disease outbreaks in human, wildlife, and domesticated species are increasing (2-5). These concurrent patterns have prompted suggestions that biodiversity and the spread of diseases may be causally linked. For example, the dilution effect hypothesis proposes that diverse host communities inhibit the abundance of parasites through several mechanisms, such as regulating populations of susceptible hosts or interfering with the transmission process (6-8). Thus, diverse communities may inhibit the proliferation of parasites, thereby promoting the stability of ecological communities and ecosystem services (e.g., nutrient cycling, carbon sequestration, and natural product production) (9).Understanding the generality of these dilution effects is crucial for projections of future disease outbreaks, which can threaten human health, species conservation, and ecosystem services (3, 9). If biodiversity generally inhibits parasites, then human-driven biodiversity loss could exacerbate disease risk for humans and wildlife. Biodiversity conservation might then limit the abundance of many parasites of wildlife and humans (10-12). However, if parasites a...

RECENT decades have witnessed changes in the practice of veterinary medicine (Thrusfield 1998). In developed countries, the successful control of the major infectious diseases and the resultant intensification of livestock enterprises has produced a shift in interest towards complex, frequently noninfectious, diseases, and increasing emphasis is being placed on the health of herds rather than individual animals (Brand and others 1996). In contrast, in developing countries, the control of infectious diseases is still the major problem and progress needs to be made both in the measurement of disease frequencies, for example of trypanosomiasis in Africa and Asia, and in the implementation of control and/or eradication campaigns, for example for rinderpest (IAEA 1991). These changes have required the application of quantitative epidemiological procedures (Noordhuizen 1996), notably the use of rigorous sampling theory when conducting field surveys, and observational studies to identify the risk factors associated with multifactorial diseases in both farm practice and companion animal practice. Moreover, diagnostic tests applied either to individual animals, or to animal populations in eradication campaigns, can only be interpreted correctly when their validity and reliability has been assessed. Despite a long history in veterinary medicine, many diagnostic tests, particularly serological tests, have not been so assessed.The methods and statistical theory that underpin these quantitative procedures have been described by Martin and others (1987), Thrusfield (1997), and Noordhuizen and others ( 1997), and several computer programs have been designed to facilitate the necessary computations by veterinarians and physicians. These include suites of programs, such as EPI INFO (Dean and others 1995), PEPI (Gahlinger and Abramson 1995), EPISCOPE (Frankena and others 1990) and EPIZOO (Kouba 1997), and many programs for specific, individual analyses (The Epidemiology Monitor). However, these programs have limitations, especially for users who lack a grounding in analytical techniques. The package WIN EPISCOPE 2.0 has therefore been designed to combine the procedures that are commonly used in the design and analysis of epidemiological studies into an easy-to-understand form based on Microsoft Windows.The package provides the main computational procedures used in the design and analysis of simple field surveys, in control campaigns and observational studies, and in the assessment of diagnostic tests, and includes an introduction to basic mathematical modelling of infectious diseases. For each computation, comprehensive'Help' menus are provided which describe the techniques and list, with references, the formulae that are used. The package is an improved and expanded version of EPISCOPE for MS DOS (Frankena and others 1990) and of its first Microsoft Windows release, WIN EPISCOPE 1.0 (Ortega and others 1996).

Humans are altering the distribution of species by changing the climate and disrupting biotic interactions and dispersal. A fundamental hypothesis in spatial ecology suggests that these effects are scale dependent; biotic interactions should shape distributions at local scales, whereas climate should dominate at regional scales. If so, common single-scale analyses might misestimate the impacts of anthropogenic modifications on biodiversity and the environment. However, large-scale datasets necessary to test these hypotheses have not been available until recently. Here we conduct a crosscontinental, cross-scale (almost five orders of magnitude) analysis of the influence of biotic and abiotic processes and human population density on the distribution of three emerging pathogens: the amphibian chytrid fungus implicated in worldwide amphibian declines and West Nile virus and the bacterium that causes Lyme disease (Borrelia burgdorferi), which are responsible for ongoing human health crises. In all three systems, we show that biotic factors were significant predictors of pathogen distributions in multiple regression models only at local scales (∼10 2 -10 3 km 2 ), whereas climate and human population density always were significant only at relatively larger, regional scales (usually >10 4 km 2 ). Spatial autocorrelation analyses revealed that biotic factors were more variable at smaller scales, whereas climatic factors were more variable at larger scales, as is consistent with the prediction that factors should be important at the scales at which they vary the most. Finally, no single scale could detect the importance of all three categories of processes. These results highlight that common single-scale analyses can misrepresent the true impact of anthropogenic modifications on biodiversity and the environment.ecology | dilution effect | chytridiomycosis | West Nile virus | Lyme disease

Resource availability can significantly alter host-parasite dynamics. Abundant food can provide more resources for hosts to resist infections, but also increase host tolerance of infections by reducing competition between hosts and parasites for food. Whether abundant food favors host resistance or tolerance (or both) might depend on the type of resource that the parasite exploits (e.g. host tissue vs. food), which can vary based on the stage of infection. In our study, we evaluated how low and high resource diets affect Cuban tree frog (Osteopilus septentrionalis) resistance and tolerance of a skin-penetrating, gut nematode Aplectana sp. at each stage of the infection. Compared to a low resource diet, a high resource diet enhanced frog resistance to worm penetration and tolerance while worms traveled to the gut. In contrast, a low resource diet increased resistance to establishment of the infection. After the infection established and worms could access food resources in the gut, a high resource diet enhanced host tolerance of parasites. On a high resource diet, parasitized frogs consumed significantly more food than non-parasitized frogs; when food was then restricted, mass of non-parasitized frogs did not change whereas mass of parasitized frogs decreased significantly. Thus, a high resource diet increased frog tolerance of established worms because frogs could fully compensate for energy lost to the parasites. Our study shows that host-parasite dynamics are influenced by the effect of resource availability on host resistance and tolerance, which depends on when parasites have access to food and the stage of infection.

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To get a better insight into the role of birds as reservoirs of extended-spectrum β-lactamase (ESBL) and plasmidic AmpC β-lactamase (pAmpC) Escherichia coli producers, 100 fecal samples belonging to 15 different wild avian species from Northern Spain were analyzed. Cefotaxime-resistant (CTX) E. coli isolates were identified in 16 of the 100 tested birds, which corresponded to 9 animal species (Gyps fulvus-griffon vulture, Larus michahellis-yellow-legged gull, Milvus migrans-black kite, Milvus milvus-red kite, Ciconia ciconia-white stork, Sturnus unicolor-spotless starling, Aquila chrysaetos-golden eagle, Cuculus canorus-common cuckoo, Tyto alba-barn owl). Fifteen isolates harbored ESBL or pAmpC-encoding genes (number of isolates): bla (9), bla (3), bla (2), and bla (1). The last CTX isolate presented a -42-point-mutation in the chromosomal ampC promoter. Eleven out of 15 ESBL/pAmpC E. coli isolates were multiresistant (most common resistance phenotype: β-lactams-quinolones-tetracycline-sulfamethoxazole/trimethoprim). A plasmid-mediated quinolone resistance determinant (qnrS1) was identified in one E. coli from a barn owl. High genetic diversity was observed among ESBL/pAmpC E. coli isolates, with 12 different sequence types (STs), including several strains of STs frequently detected among human clinical isolates (ST38/D, ST131/B2, ST155/B1, ST10/A). The ST131 isolate belonged to the emergent ciprofloxacin-resistant H30R subclone. This study reveals a high percentage of bird as carriers of ESBL/pAmpC E. coli isolates in Spain, highlighting the elevated rate among storks, kites, and vultures. Wild birds can contribute to the global spread of ESBL/pAmpC-producing E. coli in natural ecosystems.

This meta-analysis of reports examining ticks throughout the Western Palearctic region indicates a distinct geographic pattern for Borrelia burgdorferi sensu lato prevalence in questing nymphal Ixodes ricinus ticks. The greatest prevalence was reported between the 5°E and 25°E longitudes based on an analysis of 123 collection points with 37,940 nymphal tick specimens (87.43% of total nymphs; 56.35% of total ticks in the set of reports over the target area). Climatic traits, such as temperature and vegetation stress, and their seasonality correlated with Borrelia prevalence in questing ticks. The greatest prevalence was associated with mild winter, high summer, and low seasonal amplitude of temperatures within the range of the tick vector, higher vegetation indices in the May-June period, and well-connected vegetation patches below a threshold at which rates suddenly drop. Classification of the target territory using a qualitative risk index derived from the abiotic variables produced an indicator of the probability of finding infected ticks in the Western Palearctic region. No specific temporal trends were detected in the reported prevalence. The ranges of the different B. burgdorferi sensu lato genospecies showed a pattern of high biodiversity between 4°W and 20°E, partially overlapping the area of highest prevalence in ticks. Borrelia afzelii and Borrelia garinii are the dominant species in central Europe (east of ϳ25°E), but B. garinii may appear alone at southern latitudes and Borrelia lusitaniae is the main indicator species for meridional territories.

The impact of climate trends during the period 1901–2009 on the life cycle of Hyalomma marginatum in Europe was modeled to assess changes in the physiological processes of this threat to public health. Monthly records of temperature and water vapour at a resolution of 0.5° and equations describing the life cycle processes of the tick were used. The climate in the target region affected the rates of the life cycle processes of H. marginatum: development rates increased, mortality rates in molting stages decreased, and the survival rates of questing ticks decreased in wide territories of the Mediterranean basin. The modeling framework indicated the existence of critical areas in the Balkans, central Europe, and the western coast of France, where the physiological processes of the tick improved to extents that are consistent with the persistence of populations if introduced. A spatially explicit risk assessment was performed to detect candidate areas where active surveys should be performed to monitor changes in tick density or persistence after a hypothetical introduction. We detected areas where the critical abiotic (climate) and biotic (host density) factors overlap, including most of the Iberian peninsula, the Mediterranean coast of France, eastern Turkey, and portions of the western Black Sea region. Wild ungulate densities are unavailable for large regions of the territory, a factor that might affect the outcome of the study. The risk of successfully establishing H. marginatum populations at northern latitudes of its current colonization range seems to be still low, even if the climate has improved the performance of the tick in these areas.