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

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 Kultura organizacyjna jako moderator związków pomiędzy zaufaniem organizacyjnym a jego determinantami i następstwami

2021 ◽  
Vol 65 (1) ◽  
pp. 169-196
Author(s):  
Lech Górniak ◽  
Keyword(s):  
Organizational Culture ◽  
Organizational Trust ◽  
Field Studies ◽  
Industry Type ◽  
Type Size ◽  
The Impact ◽  
The Relationship ◽  
Do So

The paper includes analysis of the results of field studies conducted among employees of 20 organizations (N=601). The analyses were aimed at determining the impact of organizational culture has on the relationships between the “soft” (psychological and social) factors that characterize them. In particular the impact of organizational culture was considered on the relationship between the antecedents and outcomes of organizational trust. The statistical method used was moderation analysis (Hayes, 2018). The studies were based on a questionnaire that included 13 scales as measures for the variables considered. The analyses provides two main conclusions. The first is for researchers dealing with the soft aspects of the organization’s functioning, especially those related to the role of trust in the organization. The second is addressed to practitioners and relates to the quality of knowledge on employee management. The conclusion for the researchers concerns the need to take into account the specificity of a given organization when describing organizational phenomena. This concerns the tacit factors that go beyond the standard characteristics (industry type, size of the organization, number of employees, etc.), in particular those aspects of the organizational culture related to organizational trust. The failure to do so may lead to inadequate advice for executives regarding the methods used to develop the organization’s potential. The conclusion for practitioners is the need to pay attention to how employees perceive the organizational culture of their company. The omission of this fact may adversely affect the strategy of building a climate of trust, which can lead to a decrease in teamwork quality and a reduction in the superior-subordinate relationship.

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 Megacities as drivers of national outbreaks: the role of holiday travel in the spread of infectious diseases

2019 ◽  
Author(s):  
Ayesha S. Mahmud ◽  
Md. Iqbal Kabir ◽  
Kenth Engø-Monsen ◽  
Sania Tahmina ◽  
Baizid Khoorshid Riaz ◽  
...  
Keyword(s):  
Infectious Diseases ◽  
Large Scale ◽  
Disease Risk ◽  
Human Mobility ◽  
Mobile Phone Data ◽  
Dhaka City ◽  
Population Mobility ◽  
Time Data ◽  
The Impact

AbstractHuman mobility connects populations and can lead to large fluctuations in population density, both of which are important drivers of epidemics. Measuring population mobility during infectious disease outbreaks is challenging, but is a particularly important goal in the context of rapidly growing and highly connected urban centers in low and middle income countries, which can act to amplify and spread local epidemics nationally and internationally. Here, we combine estimates of population movement from mobile phone data for over 4 million subscribers in the megacity of Dhaka, Bangladesh, one of the most densely populated cities globally. We combine mobility data with epidemiological data from a household survey, to understand the role of population mobility on the spatial spread of the mosquito-borne virus chikungunya within and outside Dhaka city during a large outbreak in 2017. The peak of the 2017 chikungunya outbreak in Dhaka coincided with the annual Eid holidays, during which large numbers of people traveled from Dhaka to their native region in other parts of the country. We show that regular population fluxes around Dhaka city played a significant role in determining disease risk, and that travel during Eid was crucial to the spread of the infection to the rest of the country. Our results highlight the impact of large-scale population movements, for example during holidays, on the spread of infectious diseases. These dynamics are difficult to capture using traditional approaches, and we compare our results to a standard diffusion model, to highlight the value of real-time data from mobile phones for outbreak analysis, forecasting, and surveillance.

scholarly journals Respiratory Disease Risk of Zoo-Housed Bonobos Is Associated with Sex and Betweenness Centrality in the Proximity Network

Animals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3597
Author(s):  
Jonas R. R. Torfs ◽  
Marcel Eens ◽  
Daan W. Laméris ◽  
Nicky Staes
Keyword(s):  
Social Network ◽  
Respiratory Disease ◽  
Betweenness Centrality ◽  
Disease Risk ◽  
Winter Season ◽  
Network Position ◽  
Increased Risk ◽  
The Impact ◽  
Social Network Position

Infectious diseases can be considered a threat to animal welfare and are commonly spread through both direct and indirect social interactions with conspecifics. This is especially true for species with complex social lives, like primates. While several studies have investigated the impact of sociality on disease risk in primates, only a handful have focused on respiratory disease, despite it being a major cause of morbidity and mortality in both wild and captive populations and thus an important threat to primate welfare. Therefore, we examined the role of social-network position on the occurrence of respiratory disease symptoms during one winter season in a relatively large group of 20 zoo-housed bonobos with managed fission-fusion dynamics. We found that within the proximity network, symptoms were more likely to occur in individuals with higher betweenness centrality, which are individuals that form bridges between different parts of the network. Symptoms were also more likely to occur in males than in females, independent of their social-network position. Taken together, these results highlight a combined role of close proximity and sex in increased risk of attracting respiratory disease, two factors that can be taken into account for further welfare management of the species.

Smallholders and Farmworkers in Agricultural Value Chains: No Upgrading Without Collective Action and State Support

2021 ◽  
pp. 1-23
Author(s):  
Ismail Doga Karatepe ◽  
Christoph Scherrer
Keyword(s):  
Field Studies ◽  
Theoretical Explanation ◽  
Government Support ◽  
Value Chains ◽  
Labor Laws ◽  
Role Of The State ◽  
Economic Upgrading ◽  
The Impact ◽  
Social Upgrading

Abstract This article presents findings from field studies of smallholders and farmworkers producing coffee, mangoes, and rice in several countries in the global South. It is one of the few comparative studies of the constraints and opportunities for social upgrading in global agricultural value chains (gvcs). We argue that the ease with which new suppliers can be found gives highly concentrated global wholesalers and retailers enormous leverage over smallholders. As a result, opportunities for social upgrading tend to be limited. Even in successful cases, it is accompanied by fewer employment opportunities. Cooperatives, which enjoy government support and enforced labor laws, are an exception. The article begins with a discussion of problems in measuring the impact of gvc participation and a theoretical explanation of why economic upgrading is not sufficient to ensure social upgrading. Special attention is given to the role of the state in promoting social upgrading.

Assessing the impact of diseases and their control on livestock productivity: the rôle of quantitative epidemiology

1998 ◽  
Vol 21 ◽  
pp. 111-119
Author(s):  
B. D. Perry ◽  
J. J. McDermott
Keyword(s):  
Impact Assessment ◽  
Geographical Information Systems ◽  
Research Priorities ◽  
Field Studies ◽  
Geographical Information ◽  
Quantitative Epidemiology ◽  
Infection Dynamics ◽  
Increasing Demand ◽  
Livestock Productivity ◽  
The Impact

AbstractIn determining research priorities, as well as in evaluating the relative merits of different disease control options, there is an increasing demand for impact assessment, in order to justify and support research and development investments. In this process, quantitative epidemiology has a significant role to play. This paper first outlines the categories of impacts that diseases have on society and discusses how these can be measured. Using the example of tick-borne infections of livestock, the paper describes five quantitative epidemiological tools that can be used in impact assessment. These are: geographical information systems (GIS) to estimate disease distribution; mathematical models to quantify infection dynamics; observational field studies to link infection status with production loss; statistical models to enhance study design; and spreadsheet models for economic impact assessment. In each category, examples are given of recent studies.

scholarly journals Intestinal Pregnane X Receptor Links Xenobiotic Exposure and Hypercholesterolemia

2015 ◽  
Vol 29 (5) ◽  
pp. 765-776 ◽  
Author(s):  
Yipeng Sui ◽  
Robert N. Helsley ◽  
Se-Hyung Park ◽  
Xiulong Song ◽  
Zun Liu ◽  
...  
Keyword(s):  
Cardiovascular Disease ◽  
Disease Risk ◽  
Cardiovascular Disease Risk ◽  
Pregnane X Receptor ◽  
Lipid Uptake ◽  
Xenobiotic Exposure ◽  
Increased Risk ◽  
The Impact

Abstract Recent studies have associated endocrine-disrupting chemical (EDC) exposure with the increased risk of cardiovascular disease in humans, but the underlying mechanisms responsible for these associations remain elusive. Many EDCs have been implicated in activation of the nuclear receptor pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism in the liver and intestine. Here we report an important role of intestinal PXR in linking xenobiotic exposure and hyperlipidemia. We identified tributyl citrate (TBC), one of a large group of Food and Drug Administration–approved plasticizers for pharmaceutical or food applications, as a potent and selective PXR agonist. TBC efficiently activated PXR and induced PXR target gene expression in vitro and in vivo. Interestingly, TBC activated intestinal PXR but did not affect hepatic PXR activity. Exposure to TBC increased plasma total cholesterol and atherogenic low-density lipoprotein cholesterol levels in wild-type mice, but not in PXR-deficient mice. TBC-mediated PXR activation stimulated the expression of an essential cholesterol transporter, Niemann-Pick C1-like 1 (NPC1L1), in the intestine. Promoter analysis revealed a DR-4 type of PXR response element in the human NPC1L1 promoter, and TBC promoted PXR recruitment onto the NPC1L1 promoter. Consistently, TBC treatment significantly increased lipid uptake by human and murine intestinal cells and deficiency of PXR inhibited TBC-elicited lipid uptake. These findings provide critical mechanistic insight for understanding the impact of EDC-mediated PXR activation on lipid homeostasis and demonstrate a potential role of PXR in mediating the adverse effects of EDCs on cardiovascular disease risk in humans.

scholarly journals The impact of the undetected COVID-19 cases on its transmission dynamics

2020 ◽  
Author(s):  
Sujata Saha ◽  
Sumanta Saha
Keyword(s):  
Basic Reproduction Number ◽  
Reproduction Number ◽  
Disease Risk ◽  
Transmission Dynamics ◽  
Transmission Model ◽  
Risk Of Infection ◽  
Infection Transmission ◽  
Reported Data ◽  
The Impact

AbstractObjectiveThe COVID-19 pandemic is currently ongoing. Presently, due to the unavailability of a definitive vaccine to decrease its acquiring, it’s essential to understand its transmissibility in the community by undetected cases to control its transmission. This study aims to study this context using mathematical modelling.MethodsA COVID-19 transmission model was framed that estimated the basic reproduction number (R0, a measurement of disease risk) using the next-generation method. It explored the contribution of exposed and infected (detected and undetected) individuals, and environmental pathogen to the overall risk of infection spreading, utilizing the publicly reported data of this infection in Maharashtra between March 22, 2020, and May 4, 2020. A sensitivity analysis was performed to study the effect of a rising number of undetected cases to R0.ResultsThe estimated basic reproduction number is R0 = 4.63, which increases rapidly with the rise in the undetected COVID-19 cases. Although the exposed individuals made the largest contribution to infection transmission (R1 = 2.42), the contaminated environment also played a significant role.ConclusionsIt is crucial to identify the individuals exposed and infected to COVID-19 disease and isolate them to control its transmission. The awareness of the role of fomites in infection transmission is also important in this regard.

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