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.

Biodiversity series: The function of biodiversity in the ecology of vector-borne zoonotic diseases

2000 ◽  
Vol 78 (12) ◽  
pp. 2061-2078 ◽  
Author(s):  
Richard S Ostfeld ◽  
Felicia Keesing
Keyword(s):  
Species Diversity ◽  
Lyme Disease ◽  
Host Species ◽  
Disease Risk ◽  
Feeding Habits ◽  
Dilution Effect ◽  
Tick Population ◽  
Infection Prevalence ◽  
Vector Borne ◽  
The Impact

This is a critical evaluation of the influence of species diversity within communities of vertebrates on the risk of human exposure to vector-borne zoonoses. Vertebrates serve as natural reservoirs of many disease agents (viral, bacterial, protozoal) that are transmitted to humans by blood-feeding arthropod vectors. We describe the natural history of the Lyme disease zoonosis to illustrate interactions among pathogens, vectors, vertebrate hosts, and risk to humans. We then describe how the presence of a diverse assemblage of vertebrates can dilute the impact of the principal reservoir (the white-footed mouse, Peromyscus leucopus) of Lyme disease spirochetes (Borrelia burgdorferi), thereby reducing the disease risk to humans. Exploring the logic of what we call the dilution effect reveals four conditions that are necessary for it to apply generally to vector-borne zoonoses: (1) the feeding habits of the vector are generalized; (2) the pathogen is acquired by the vector from hosts (as opposed to exclusively transovarial transmission); (3) reservoir competence (the ability of a particular host species to infect a vector) varies among host species; and (4) the most competent reservoir host tends to be a community dominant, as defined by the proportion of the tick population fed by that species. When these conditions are met, vertebrate communities with high species diversity will contain a greater proportion of incompetent reservoir hosts that deflect vector meals away from the most competent reservoirs, thereby reducing infection prevalence and disease risk. Incorporating the likelihood that the abundance of competent reservoirs is reduced in more diverse communities, owing to the presence of predators and competitors, reinforces the impact of the dilution effect on the density of infected vectors. A review of the literature reveals the generality, though not the universality, of these conditions, which suggests that the effects of diversity on disease risk may be widespread. Issues in need of further exploration include (i) the relative importance of diversity per se versus fluctuating numbers of particular species; (ii) the relevance of species richness versus evenness to the dilution effect; (iii) whether the dilution effect operates at both local and regional scales; and (iv) the shape of empirically determined curves relating diversity to measures of disease risk. Further studies linking community ecology with epidemiology are warranted.

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.

Disruption of a host-parasite system following the introduction of an exotic host species

Parasitology ◽  
2005 ◽  
Vol 130 (6) ◽  
pp. 661-668 ◽  
Author(s):  
S. TELFER ◽  
K. J. BOWN ◽  
R. SEKULES ◽  
M. BEGON ◽  
T. HAYDEN ◽  
...  
Keyword(s):  
Bank Vole ◽  
Host Species ◽  
Negative Relationship ◽  
Dilution Effect ◽  
Wood Mouse ◽  
Clethrionomys Glareolus ◽  
Infection Prevalence ◽  
Wood Mice ◽  
Effect Hypothesis ◽  
Host Parasite

The potential of biological invasions to threaten native ecosystems is well recognized. Here we describe how an introduced species impacts on native host-parasite dynamics by acting as an alternative host. By sampling sites across an invasion front in Ireland, we quantified the influence of the introduced bank vole (Clethrionomys glareolus) on the epidemiology of infections caused by flea-transmitted haemoparasites of the genusBartonellain native wood mice (Apodemus sylvaticus).Bartonellainfections were detected on either side of the front but occurred exclusively in wood mice, despite being highly prevalent in both rodent species elsewhere in Europe. Bank vole introduction has, however, affected the wood mouse-Bartonellainteraction, with the infection prevalence of bothBartonella birtlesiiandBartonella tayloriideclining significantly with increasing bank vole density. Whilst flea prevalence in wood mice increases with wood mouse density in areas without bank voles, no such relationship is detected in invaded areas. The results are consistent with the dilution effect hypothesis. This predicts that for vector-transmitted parasites, the presence of less competent host species may reduce infection prevalence in the principal host. In addition we found a negative relationship betweenB. birtlesiiandB. tayloriiprevalences, indicating that these two microparasites may compete within hosts.

Snail species diversity impacts the infection patterns of Echinostoma spp.: Examples from field collected data

2017 ◽  
Vol 62 (3) ◽  
Author(s):  
Michael R. Zimmermann ◽  
Kyle E. Luth ◽  
Gerald W. Esch
Keyword(s):  
Species Diversity ◽  
Disease Risk ◽  
Dilution Effect ◽  
Field Studies ◽  
Snail Species ◽  
Larval Stages ◽  
Infection Dynamics ◽  
Risk Of Disease ◽  
The Impact

AbstractRapid losses of biodiversity due to the changing landscape have spurred increased interest in the role of species diversity and disease risk. A leading hypothesis for the importance of biodiversity in disease reduction is the dilution effect, which suggests that increasing species diversity within a system decreases the risk of disease among the organisms inhabiting it. The role of species diversity in trematode infection was investigated using field studies from sites across the U.S. to examine the impact of snail diversity in the infection dynamics of both first and second intermediate larval stages of

scholarly journals Bushmeat and zoonoses threats warrant need for national zoonoses combat inter-disciplinary research partnership, evolving citizen science and policy ban of trade and consumption

2020 ◽  
Vol 7 (1) ◽  
pp. 68
Author(s):  
Ansu Thomas
Keyword(s):  
Species Diversity ◽  
Citizen Science ◽  
Disease Transmission ◽  
Meta Analysis ◽  
Dilution Effect ◽  
Research Partnership ◽  
Mammal Species ◽  
Science And Policy ◽  
Deforestation Rate ◽  
Bat Coronavirus

<p class="Noindentpara">“We must find them before they find us” said Dr.Shi, Bat Virologist”. Indian bat species diversity stands 127 ssp and China 147 bat ssp. Indian publications online (2000-2020), searching “bat”, “Chiroptera”, “India”, retrieved results viz., 191 (Elsevier); 27 (Scopus) and 0 (Wiley). For China, 594 publications exist (2000-2017)2; Himalayan cave bat biodiversity is not systematized, average annual deforestation rate, from 2000 to 2014 being 0.5% (Bhutan, Nepal) but 1.3% in India, China. “Dilution effect”, so-called “negative diversity–disease”, says ‘biodiversity losses promote disease transmission’. Protecting natural areas from human incursion reduces zoonotic disease spillover. Emergence of bat coronavirus represents recent viral explosion reaction to declining biodiversity. Meta-analysis of 143 hunting studies from India showed 114 mammal species but bat-hunting data absent.</p>

scholarly journals Host Richness Increases Tuberculosis Disease Risk in Game-Managed Areas

2019 ◽  
Vol 7 (6) ◽  
pp. 182 ◽  
Author(s):  
Jose Angel Barasona ◽  
Christian Gortázar ◽  
José de la Fuente ◽  
Joaquín Vicente
Keyword(s):  
Species Richness ◽  
Host Species ◽  
Life Histories ◽  
Disease Risk ◽  
Dilution Effect ◽  
Pathogen Transmission ◽  
Trade Offs ◽  
Community Assemblages ◽  
Animal Communities ◽  
The Impact

Current scientific debate addresses whether species richness in animal communities may negatively moderate pathogen transmission and disease outcome (dilution effect), or to the contrary, if disease emergence benefits from more diverse community assemblages (amplification effect). The result may not depend exclusively on patterns of host species biodiversity but may depend on the specific composition of reservoir hosts and vectors, and their ecology. Host–pathogen interactions have shaped variations in parasite virulence, transmissibility and specificity. In the same way the importance of factors related to host exposure or to life history trade-offs are expected to vary. In this study, we demonstrate that ungulate host species richness correlates with increased community competence to maintain and transmit pathogens of the Mycobacterium tuberculosis complex (MTC) in game-managed areas in Mediterranean Spain. Therefore, we should consider natural and artificial variations in life histories of pathogens and host communities to characterize the impact of biodiversity on the health of diverse assemblages of human and animal communities. Since most approaches assessing epidemiology and transmission of shared pathogens only involve single- or pair-species, further research is needed to better understand the infection dynamics from complete community assemblages, at least in chronic diseases such as tuberculosis and in non-natural animal communities.

scholarly journals Biodiversity inhibits parasites: Broad evidence for the dilution effect

2015 ◽  
Vol 112 (28) ◽  
pp. 8667-8671 ◽  
Author(s):  
David J. Civitello ◽  
Jeremy Cohen ◽  
Hiba Fatima ◽  
Neal T. Halstead ◽  
Josue Liriano ◽  
...  
Keyword(s):  
Disease Risk ◽  
Meta Analysis ◽  
Host Density ◽  
Dilution Effect ◽  
Wildlife Diseases ◽  
Parasite Abundance ◽  
Effect Hypothesis ◽  
Zoonotic Parasites ◽  
Dilution Effects ◽  
Plant Herbivore

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 meta-analysis 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.

Effect of host diversity and species assemblage composition on bovine tuberculosis (bTB) risk in Ethiopian cattle

Parasitology ◽  
2017 ◽  
Vol 144 (6) ◽  
pp. 783-792 ◽  
Author(s):  
DEJENE W. SINTAYEHU ◽  
IGNAS M. A. HEITKÖNIG ◽  
HERBERT H. T. PRINS ◽  
ZEWDU K. TESSEMA ◽  
WILLEM F. DE BOER
Keyword(s):  
Species Diversity ◽  
Habitat Use ◽  
Bovine Tuberculosis ◽  
Disease Risk ◽  
Control Strategies ◽  
Dilution Effect ◽  
Tuberculin Test ◽  
Diversity Indices ◽  
Species Identity ◽  
Greater Kudu

SUMMARYCurrent theories on diversity–disease relationships describe host species diversity and species identity as important factors influencing disease risk, either diluting or amplifying disease prevalence in a community. Whereas the simple term ‘diversity’ embodies a set of animal community characteristics, it is not clear how different measures of species diversity are correlated with disease risk. We therefore tested the effects of species richness, Pielou's evenness and Shannon's diversity on bovine tuberculosis (bTB) risk in cattle in the Afar Region and Awash National Park between November 2013 and April 2015. We also analysed the identity effect of a particular species and the effect of host habitat use overlap on bTB risk. We used the comparative intradermal tuberculin test to assess the number of bTB-infected cattle. Our results suggested a dilution effect through species evenness. We found that the identity effect of greater kudu – a maintenance host – confounded the dilution effect of species diversity on bTB risk. bTB infection was positively correlated with habitat use overlap between greater kudu and cattle. Different diversity indices have to be considered together for assessing diversity–disease relationships, for understanding the underlying causal mechanisms. We posit that unpacking diversity metrics is also relevant for formulating disease control strategies to manage cattle in ecosystems characterized by seasonally limited resources and intense wildlife–livestock interactions.

scholarly journals The dilution effect behind the scenes: testing the underlying assumptions of its mechanisms through quantifying the long-term dynamics and effects of a pathogen in multiple host species

2021 ◽  
Vol 288 (1952) ◽  
pp. 20210773
Author(s):  
Mario Garrido ◽  
Snir Halle ◽  
Ron Flatau ◽  
Carmit Cohen ◽  
Álvaro Navarro-Castilla ◽  
...  
Keyword(s):  
Host Species ◽  
Disease Risk ◽  
Experimental Studies ◽  
Dilution Effect ◽  
Model System ◽  
The Other ◽  
Field Pattern ◽  
Disease Research ◽  
Recovery Potential

Disentangling the mechanisms that mediate the relationships between species diversity and disease risk has both theoretical and applied implications. We employed a model system of rodents and their Mycoplasma pathogens, in which an extreme negative diversity–disease relationship was demonstrated, to test the assumptions underlying three mechanisms that may explain this field pattern. Through quantifying the long-term dynamics and effects of the pathogen in its three host species, we estimated the between-host differences in pathogen spreading and transmission potentials, and host recovery potential and vulnerability to infection. The results suggest that one of the hosts is a pathogen amplifier and the other two hosts function as diluters. Considering the similarity in infection success and intensity among hosts, and the failure to detect any pathogen-induced damage, we could not validate the assumption underlying the hypotheses that diluters reduce the overall transmission or increase the mortality of infected hosts in the system. Instead, the results demonstrate that diluters clear the infection faster than amplifiers, supporting the possibility that the addition of diluters to the community may reduce the overall number of infected hosts through this mechanism. This study highlights the contribution of experimental studies that simultaneously explore different aspects of host–pathogen interactions in multiple hosts, in diversity–disease research.

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.

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