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.

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.

scholarly journals Linking community and disease ecology: the impact of biodiversity on pathogen transmission

2012 ◽  
Vol 367 (1604) ◽  
pp. 2807-2813 ◽  
Author(s):  
Benjamin Roche ◽  
Andrew P. Dobson ◽  
Jean-François Guégan ◽  
Pejman Rohani
Keyword(s):  
Host Species ◽  
Disease Ecology ◽  
Biodiversity Loss ◽  
Pathogen Transmission ◽  
Community Diversity ◽  
Ecological Interactions ◽  
Disease Emergence ◽  
Pathogen Dynamics ◽  
Wildlife Pathogens ◽  
The Impact

The increasing number of zoonotic diseases spilling over from a range of wild animal species represents a particular concern for public health, especially in light of the current dramatic trend of biodiversity loss. To understand the ecology of these multi-host pathogens and their response to environmental degradation and species extinctions, it is necessary to develop a theoretical framework that takes into account realistic community assemblages. Here, we present a multi-host species epidemiological model that includes empirically determined patterns of diversity and composition derived from community ecology studies. We use this framework to study the interaction between wildlife diversity and directly transmitted pathogen dynamics. First, we demonstrate that variability in community composition does not affect significantly the intensity of pathogen transmission. We also show that the consequences of community diversity can differentially impact the prevalence of pathogens and the number of infectious individuals. Finally, we show that ecological interactions among host species have a weaker influence on pathogen circulation than inter-species transmission rates. We conclude that integration of a community perspective to study wildlife pathogens is crucial, especially in the context of understanding and predicting infectious disease emergence events.

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 Experimental Evidence for Opposing Effects of High Deer Density on Tick-Borne Pathogen Prevalence and Hazard

2021 ◽  
Author(s):  
Sara Louise Gandy ◽  
Elizabeth Kilbride ◽  
Roman Biek ◽  
Caroline Millins ◽  
Lucy Gilbert
Keyword(s):  
Lyme Disease ◽  
Disease Risk ◽  
Dilution Effect ◽  
High Density ◽  
Infection Prevalence ◽  
Vegetation Height ◽  
Deer Density ◽  
Pathogen Prevalence ◽  
Tick Reproduction ◽  
The Impact

Abstract Background: Identifying the mechanisms driving disease risk is challenging for multi-host pathogens, such as Borrelia burgdorferi s.l., the tick-borne bacteria causing Lyme disease. Deer are tick reproduction hosts but do not transmit B. burgdorferi s.l., whereas rodents and birds are competent transmission hosts. Here, we use a long-term deer exclosure experiment to test three mechanisms for how high deer density might shape B. burgdorferi s.l. prevalence in ticks: increased prevalence due to higher larval tick densities facilitating high transmission on rodents (M1); alternatively, reduced B. burgdorferi s.l. prevalence because more larval ticks feed on deer rather than transmission-competent rodents (dilution effect) (M2), potentially due to ecological cascades, whereby higher deer grazing pressure lowers vegetation which decreases rodent abundance thus reducing transmission (M3).Methods: In a large enclosure where red deer stags were kept at high density (32.5 deer/km²), we used an experimental design consisting of eight plots of 0.23ha, four being fenced to simulate the absence of deer and four that were accessible to deer. In each plot we measured the density of questing nymphs and nymphal infection prevalence in spring, summer and autumn and quantified vegetation height and density, and small mammal abundance Results: Prevalence tended to be lower, though not conclusively so, in high deer density plots compared to exclosures (predicted prevalence of 1.0% vs 2.2%), suggesting that the dilution (M2) and cascade (M3) mechanisms might outweigh the increased opportunities for transmission (M1). Presence of deer at high density led to lower vegetation and fewer rodents, consistent with an ecological cascade. However, Lyme disease hazard (density of infected I. ricinus nymphs) was five times higher in high deer density plots due to tick density being 18 times higher.Conclusion: High densities of tick reproduction hosts such as deer can drive up vector-borne disease hazard, despite the potential to simultaneously reduce pathogen prevalence. This has implications for environmental pathogen management and for deer management, although the impact of intermediate deer densities now needs testing.

scholarly journals A field test of the dilution effect hypothesis in four avian multi-host pathogens

2021 ◽  
Vol 17 (6) ◽  
pp. e1009637
Author(s):  
Martina Ferraguti ◽  
Josué Martínez-de la Puente ◽  
Miguel Ángel Jiménez–Clavero ◽  
Francisco Llorente ◽  
David Roiz ◽  
...  
Keyword(s):  
Species Richness ◽  
Species Diversity ◽  
Passer Domesticus ◽  
Host Density ◽  
Dilution Effect ◽  
Pathogen Transmission ◽  
Opposite Pattern ◽  
Vector Borne ◽  
Effect Hypothesis ◽  
Community Variables

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens–three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)–and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.

scholarly journals Trypanosoma cruzi reservoir—triatomine vector co-occurrence networks reveal meta-community effects by synanthropic mammals on geographic dispersal

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3152 ◽  
Author(s):  
Carlos N. Ibarra-Cerdeña ◽  
Leopoldo Valiente-Banuet ◽  
Víctor Sánchez-Cordero ◽  
Christopher R. Stephens ◽  
Janine M. Ramsey
Keyword(s):  
Trypanosoma Cruzi ◽  
Host Species ◽  
Disease Risk ◽  
Global Climate ◽  
Host Community ◽  
Transmission Risk ◽  
Edge Density ◽  
Public Health Importance ◽  
Mammal Species ◽  
The Impact

Contemporary patterns of land use and global climate change are modifying regional pools of parasite host species. The impact of host community changes on human disease risk, however, is difficult to assess due to a lack of information about zoonotic parasite host assemblages. We have used a recently developed method to infer parasite-host interactions for Chagas Disease (CD) from vector-host co-occurrence networks. Vector-host networks were constructed to analyze topological characteristics of the network and ecological traits of species’ nodes, which could provide information regarding parasite regional dispersal in Mexico. Twenty-eight triatomine species (vectors) and 396 mammal species (potential hosts) were included using a data-mining approach to develop models to infer most-likely interactions. The final network contained 1,576 links which were analyzed to calculate centrality, connectivity, and modularity. The model predicted links of independently registeredTrypanosoma cruzihosts, which correlated with the degree of parasite-vector co-occurrence. Wiring patterns differed according to node location, while edge density was greater in Neotropical as compared to Nearctic regions. Vectors with greatest public health importance (i.e., Triatoma dimidiata,T. barberi,T. pallidipennis,T. longipennis, etc), did not have stronger links with particular host species, although they had a greater frequency of significant links. In contrast, hosts classified as important based on network properties were synanthropic mammals. The latter were the most common parasite hosts and are likely bridge species between these communities, thereby integrating meta-community scenarios beneficial for long-range parasite dispersal. This was particularly true for rodents, >50% of species are synanthropic and more than 20% have been identified asT. cruzihosts. In addition to predicting potential host species using the co-occurrence networks, they reveal regions with greater expected parasite mobility. The Neotropical region, which includes the Mexican south and southeast, and the Transvolcanic belt, had greatest potential activeT. cruzidispersal, as well as greatest edge density. This information could be directly applied for stratification of transmission risk and to design and analyze human-infected vector contact intervention efficacy.

Helminth species diversity of mammals: parasite species richness is a host species attribute

Parasitology ◽  
2008 ◽  
Vol 135 (14) ◽  
pp. 1701-1705 ◽  
Author(s):  
F. BORDES ◽  
S. MORAND
Keyword(s):  
Species Richness ◽  
Host Species ◽  
Parasite Species ◽  
Regional Scale ◽  
Large Data ◽  
Helminth Species ◽  
Future Research ◽  
Data Set ◽  
Parasite Species Richness ◽  
Trade Offs

SUMMARYStudies investigating parasite diversity have shown substantial geographical variation in parasite species richness. Most of these studies have, however, adopted a local scale approach, which may have masked more general patterns. Recent studies have shown that ectoparasite species richness in mammals seems highly repeatable among populations of the same mammal host species at a regional scale. In light of these new studies we have reinvestigated the case of parasitic helminths by using a large data set of parasites from mammal populations in 3 continents. We collected homogeneous data and demonstrated that helminth species richness is highly repeatable in mammals at a regional scale. Our results highlight the strong influence of host identity in parasite species richness and call for future research linking helminth species found in a given host to its ecology, immune defences and potential energetic trade-offs.

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 Vector Surveillance, Host Species Richness, and Demographic Factors as West Nile Disease Risk Indicators

Viruses ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 934
Author(s):  
John M. Humphreys ◽  
Katherine I. Young ◽  
Lee W. Cohnstaedt ◽  
Kathryn A. Hanley ◽  
Debra P. C. Peters
Keyword(s):  
Risk Assessment ◽  
Species Richness ◽  
Host Species ◽  
Disease Risk ◽  
The United States ◽  
Risk Indicators ◽  
Vector Surveillance ◽  
West Nile ◽  
Risk Of Death ◽  
The Us

West Nile virus (WNV) is the most common arthropod-borne virus (arbovirus) in the United States (US) and is the leading cause of viral encephalitis in the country. The virus has affected tens of thousands of US persons total since its 1999 North America introduction, with thousands of new infections reported annually. Approximately 1% of humans infected with WNV acquire neuroinvasive West Nile Disease (WND) with severe encephalitis and risk of death. Research describing WNV ecology is needed to improve public health surveillance, monitoring, and risk assessment. We applied Bayesian joint-spatiotemporal modeling to assess the association of vector surveillance data, host species richness, and a variety of other environmental and socioeconomic disease risk factors with neuroinvasive WND throughout the conterminous US. Our research revealed that an aging human population was the strongest disease indicator, but climatic and vector-host biotic interactions were also significant in determining risk of neuroinvasive WND. Our analysis also identified a geographic region of disproportionately high neuroinvasive WND disease risk that parallels the Continental Divide, and extends southward from the US–Canada border in the states of Montana, North Dakota, and Wisconsin to the US–Mexico border in western Texas. Our results aid in unraveling complex WNV ecology and can be applied to prioritize disease surveillance locations and risk assessment.

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