A Candide response to Panglossian accusations by Randolph and Dobson: biodiversity buffers disease

Parasitology ◽  
2013 ◽  
Vol 140 (10) ◽  
pp. 1196-1198 ◽  
Author(s):  
RICHARD S. OSTFELD
Keyword(s):  
Infectious Disease ◽  
Disease Risk ◽  
Negative Relationship ◽  
Dilution Effect ◽  
Widespread Phenomenon ◽  
High Diversity

SUMMARYRandolph and Dobson (2012) criticize the dilution effect, which describes the negative relationship between biodiversity and infectious disease risk. Unfortunately, their commentary includes distortions, errors of omission, and errors of commission, which are rebutted herein. Contrary to their claims, the dilution effect is not a ‘mantra’ that asserts that reduced disease risk is a ‘universal’ outcome of high diversity. Although universality of the dilution effect has not been claimed, and conditions under which diversity can amplify disease risk have been described, the growing literature indicates that the dilution effect is indeed a widespread phenomenon.

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

2017 ◽  
Vol 372 (1722) ◽  
pp. 20160173 ◽  
Author(s):  
Christina L. Faust ◽  
Andrew P. Dobson ◽  
Nicole Gottdenker ◽  
Laura S. P. Bloomfield ◽  
Hamish I. McCallum ◽  
...  
Keyword(s):  
Infectious Disease ◽  
Habitat Loss ◽  
Disease Risk ◽  
Dilution Effect ◽  
Well Being ◽  
Pathogen Transmission ◽  
Policy Implications ◽  
Infection Prevalence ◽  
Density Dependent ◽  
Host Competence

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'.

The diversity–disease relationship: evidence for and criticisms of the dilution effect

Parasitology ◽  
2016 ◽  
Vol 143 (9) ◽  
pp. 1075-1086 ◽  
Author(s):  
Z. Y. X. HUANG ◽  
F. VAN LANGEVELDE ◽  
A. ESTRADA-PEÑA ◽  
G. SUZÁN ◽  
W. F. DE BOER
Keyword(s):  
Species Diversity ◽  
Host Species ◽  
Disease Risk ◽  
Current Knowledge ◽  
Risk Measures ◽  
Extinction Risk ◽  
Meta Analysis ◽  
Negative Relationship ◽  
Dilution Effect ◽  
Landscape Fragmentation

SUMMARYThe dilution effect, that high host species diversity can reduce disease risk, has attracted much attention in the context of global biodiversity decline and increasing disease emergence. Recent studies have criticized the generality of the dilution effect and argued that it only occurs under certain circumstances. Nevertheless, evidence for the existence of a dilution effect was reported in about 80% of the studies that addressed the diversity–disease relationship, and a recent meta-analysis found that the dilution effect is widespread. We here review supporting and critical studies, point out the causes underlying the current disputes. The dilution is expected to be strong when the competent host species tend to remain when species diversity declines, characterized as a negative relationship between species’ reservoir competence and local extinction risk. We here conclude that most studies support a negative competence–extinction relationship. We then synthesize the current knowledge on how the diversity–disease relationship can be modified by particular species in community, by the scales of analyses, and by the disease risk measures. We also highlight the complex role of habitat fragmentation in the diversity–disease relationship from epidemiological, evolutionary and ecological perspectives, and construct a synthetic framework integrating these three perspectives. We suggest that future studies should test the diversity–disease relationship across different scales and consider the multiple effects of landscape fragmentation.

scholarly journals Dilution effect in bovine tuberculosis: risk factors for regional disease occurrence in Africa

2013 ◽  
Vol 280 (1765) ◽  
pp. 20130624 ◽  
Author(s):  
Zheng Y. X. Huang ◽  
Willem F. de Boer ◽  
Frank van Langevelde ◽  
Chi Xu ◽  
Karim Ben Jebara ◽  
...  
Keyword(s):  
Bovine Tuberculosis ◽  
Disease Risk ◽  
Negative Relationship ◽  
Dilution Effect ◽  
Single Species ◽  
Economic Losses ◽  
African Buffalo ◽  
Mammal Species ◽  
Disease Occurrence ◽  
Regional Disease

Changes in host diversity have been postulated to influence the risk of infectious diseases, including both dilution and amplification effects. The dilution effect refers to a negative relationship between biodiversity and disease risk, whereas the amplification effect occurs when biodiversity increases disease risk. We tested these effects with an influential disease, bovine tuberculosis (BTB), which is widespread in many countries, causing severe economic losses. Based on the BTB outbreak data in cattle from 2005 to 2010, we also tested, using generalized linear mixed models, which other factors were associated with the regional BTB presence in cattle in Africa. The interdependencies of predictors and their correlations with BTB presence were examined using path analysis. Our results suggested a dilution effect, where increased mammal species richness was associated with reduced probability of BTB presence after adjustment for cattle density. In addition, our results also suggested that areas with BTB infection in the preceding year, higher cattle density and larger percentage of area occupied by African buffalo were more likely to report BTB outbreaks. Climatic variables only indirectly influenced the risk of BTB presence through their effects on cattle density and wildlife distribution. Since most studies investigating the role of wildlife species on BTB transmission only involve single-species analysis, more efforts are needed to better understand the effect of the structure of wildlife communities on BTB dynamics.

Diversifying forest communities may change Lyme disease risk: extra dimension to the dilution effect in Europe

Parasitology ◽  
2016 ◽  
Vol 143 (10) ◽  
pp. 1310-1319 ◽  
Author(s):  
SANNE C. RUYTS ◽  
EVY AMPOORTER ◽  
ELENA C. COIPAN ◽  
LANDER BAETEN ◽  
DIETER HEYLEN ◽  
...  
Keyword(s):  
North America ◽  
Lyme Disease ◽  
Borrelia Burgdorferi ◽  
Disease Risk ◽  
Severe Disease ◽  
Dilution Effect ◽  
Ixodid Ticks ◽  
Infection Prevalence ◽  
Host Diversity ◽  
Pine Stands

SUMMARYLyme disease is caused by bacteria of theBorrelia burgdorferigenospecies complex and transmitted by Ixodid ticks. In North America only one pathogenic genospecies occurs, in Europe there are several. According to the dilution effect hypothesis (DEH), formulated in North America, nymphal infection prevalence (NIP) decreases with increasing host diversity since host species differ in transmission potential. We analysedBorreliainfection in nymphs from 94 forest stands in Belgium, which are part of a diversification gradient with a supposedly related increasing host diversity: from pine stands without to oak stands with a shrub layer. We expected changing tree species and forest structure to increase host diversity and decrease NIP. In contrast with the DEH, NIP did not differ between different forest types. Genospecies diversity however, and presumably also host diversity, was higher in oak than in pine stands. Infected nymphs tended to harbourBorrelia afzeliiinfection more often in pine stands whileBorrelia gariniiandBorrelia burgdorferiss. infection appeared to be more prevalent in oak stands. This has important health consequences, since the latter two cause more severe disease manifestations. We show that the DEH must be nuanced for Europe and should consider the response of multiple pathogenic genospecies.

scholarly journals Effect of Hand Hygiene on Infectious Disease Risk in the Community Setting: A Meta-Analysis

2008 ◽  
Vol 98 (8) ◽  
pp. 1372-1381 ◽  
Author(s):  
Allison E. Aiello ◽  
Rebecca M. Coulborn ◽  
Vanessa Perez ◽  
Elaine L. Larson
Keyword(s):  
Infectious Disease ◽  
Hand Hygiene ◽  
Disease Risk ◽  
Meta Analysis ◽  
Community Setting

Towards a mechanistic understanding of competence: a missing link in diversity–disease research

Parasitology ◽  
2020 ◽  
Vol 147 (11) ◽  
pp. 1159-1170 ◽  
Author(s):  
Tara E. Stewart Merrill ◽  
Pieter T. J. Johnson
Keyword(s):  
Infectious Disease ◽  
Community Ecology ◽  
Dilution Effect ◽  
Biodiversity Loss ◽  
Current Evidence ◽  
Clear Understanding ◽  
Future Directions ◽  
Disease Research ◽  
Mechanistic Understanding

AbstractBiodiversity loss may increase the risk of infectious disease in a phenomenon known as the dilution effect. Circumstances that increase the likelihood of disease dilution are: (i) when hosts vary in their competence, and (ii) when communities disassemble predictably, such that the least competent hosts are the most likely to go extinct. Despite the central role of competence in diversity–disease theory, we lack a clear understanding of the factors underlying competence, as well as the drivers and extent of its variation. Our perspective piece encourages a mechanistic understanding of competence and a deeper consideration of its role in diversity–disease relationships. We outline current evidence, emerging questions and future directions regarding the basis of competence, its definition and measurement, the roots of its variation and its role in the community ecology of infectious disease.

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