Host-species diversity and the transmission of vector-borne disease in low-income countries

2018 ◽  
Author(s):  
Heather Ferguson ◽  
Patrick Brock ◽  
Steve Torr
Keyword(s):  
Species Diversity ◽  
Low Income ◽  
Host Species ◽  
Pathogen Transmission ◽  
Low Income Countries ◽  
Potential Contribution ◽  
Theoretical Frameworks ◽  
Host Diversity ◽  
Vector Borne ◽  
Dilution Effects

The term “dilution effect” describes scenarios where pathogen transmission is reduced as host diversity increases. Theoretical frameworks exist to predict conditions under which dilution effects may arise, with vector-borne diseases (VBDs) being particularly susceptible to host diversity. However, to date, empirical investigation of dilution effects has been restricted to a few temperate VBD systems. We review the potential contribution of dilution effects for VBDs of greatest public health importance in low-income, typically tropical, countries. Using examples, we discuss how the underlying ecology of pathogen and vector species combine to determine the response of the disease system to biodiversity. We review cases demonstrating how manipulation of host-species diversity has altered human exposure risk. We caution that attempts to control VBDs by manipulating host diversity are unlikely to succeed, and may even be detrimental, without having a detailed understanding of the local ecology of the specific VBD and environmental setting.

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 The dilution effect in a freshwater mutualism: impacts of introduced host species on native symbionts

2021 ◽  
Author(s):  
Robert Creed ◽  
Gretchen L. Bailey ◽  
James Skelton ◽  
Bryan L. Brown
Keyword(s):  
Host Species ◽  
Host Density ◽  
Dilution Effect ◽  
Negative Effects ◽  
Parasite Abundance ◽  
Host Diversity ◽  
Negative Effect ◽  
Dilution Effects ◽  
Native Crayfish ◽  
Native Host

The dilution effect was originally proposed to describe the negative effect of increased host diversity on parasite abundance; with greater host diversity, parasite levels per host are predicted to be lower due to a higher probability of dispersing parasites encountering non-competent hosts. Dilution effects could also occur in many mutualisms if dispersing symbionts encounter hosts that vary in their competency. The introduction of non-native hosts can change community competency of a local group of host species. Crayfish introductions are occurring world-wide and these introductions are likely disrupting native crayfish-symbiont systems. Branchiobdellidan symbionts declined on native Cambarus crayfish occurring in the presence and absence of non-native Faxonius crayfish in the New River, USA. We performed an experiment investigating the effect of host density (1 vs 2 native hosts) and host diversity (1 native host and 1 introduced host) on branchiobdellidan abundance. The introduced F. cristavarius is a non-competent host for these worms. Six C. ingens were stocked on a C. chasmodactylus in each treatment and worm numbers were followed over 34 days. Worm numbers decreased over time on C. chasmodactylus alone and in the treatment in which a C. chasmodactylus was paired with an F. cristavarius. Worm numbers remained highest in the 2 C. chasmodactylus treatment . There was no significant effect of host diversity on worm reproduction. Crayfish invasions may have negative effects on mutualistic symbionts depending on the competence of introduced hosts. Loss of native symbionts is one of the potential hidden, negative effects of invasions on native freshwater diversity.

scholarly journals Social network fragmentation and community health

2017 ◽  
Vol 114 (36) ◽  
pp. E7425-E7431 ◽  
Author(s):  
Goylette F. Chami ◽  
Sebastian E. Ahnert ◽  
Narcis B. Kabatereine ◽  
Edridah M. Tukahebwa
Keyword(s):  
Community Health ◽  
Low Income ◽  
Health Workers ◽  
Treatment Compliance ◽  
Pathogen Transmission ◽  
Health Interventions ◽  
Low Income Countries ◽  
Health Advice ◽  
Advice Networks ◽  
Community Roles

Community health interventions often seek to intentionally destroy paths between individuals to prevent the spread of infectious diseases. Immunizing individuals through direct vaccination or the provision of health education prevents pathogen transmission and the propagation of misinformation concerning medical treatments. However, it remains an open question whether network-based strategies should be used in place of conventional field approaches to target individuals for medical treatment in low-income countries. We collected complete friendship and health advice networks in 17 rural villages of Mayuge District, Uganda. Here we show that acquaintance algorithms, i.e., selecting neighbors of randomly selected nodes, were systematically more efficient in fragmenting all networks than targeting well-established community roles, i.e., health workers, village government members, and schoolteachers. Additionally, community roles were not good proxy indicators of physical proximity to other households or connections to many sick people. We also show that acquaintance algorithms were effective in offsetting potential noncompliance with deworming treatments for 16,357 individuals during mass drug administration (MDA). Health advice networks were destroyed more easily than friendship networks. Only an average of 32% of nodes were removed from health advice networks to reduce the percentage of nodes at risk for refusing treatment in MDA to below 25%. Treatment compliance of at least 75% is needed in MDA to control human morbidity attributable to parasitic worms and progress toward elimination. Our findings point toward the potential use of network-based approaches as an alternative to role-based strategies for targeting individuals in rural health interventions.

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 Toward a unified dilution effect theory: How competence, competition, and the transmission mechanism influence disease prevalence

2020 ◽  
Author(s):  
Michael H. Cortez ◽  
Meghan A. Duffy
Keyword(s):  
Host Species ◽  
Dilution Effect ◽  
Disease Prevalence ◽  
Pathogen Transmission ◽  
Transmission Mechanism ◽  
Infection Prevalence ◽  
Host Interactions ◽  
Host Diversity ◽  
Disease Patterns ◽  
Effect Theory

ABSTRACTBiodiversity in communities is changing globally, including the gain and loss of host species in host-pathogen communities. The dilution effect argues for a mechanistic link between increased host diversity and decreased disease in a focal host. However, we currently have a limited understanding of how the pathogen transmission mechanism and between-host interactions influence whether increased host diversity leads to increased (amplification) or decreased (dilution) infection prevalence. We use a two-host-one-pathogen model to unify theory for pathogens with environmental transmission and density-dependent and frequency-dependent direct transmission. We then identify general rules governing how the pathogen transmission mechanism and characteristics of the introduced host (disease competence and competitive ability) influence whether the introduction of a second host species increases or decreases disease prevalence in a focal host. We discuss how our results yield insight into how specific biological mechanisms shape host biodiversity-disease patterns.

Three Cases of Joubert Syndrome in a Consanguineous Syrian Family and a Interesting Case of Multinational Collaboration

2021 ◽  
Author(s):  
Davor Petrović ◽  
Vida Čulić ◽  
Zofia Swinderek-Alsayed
Keyword(s):  
Low Income ◽  
Autosomal Recessive ◽  
Autosomal Recessive Disorder ◽  
Joubert Syndrome ◽  
Interesting Case ◽  
Low Income Countries ◽  
Ocular Motor ◽  
Quality Health Care ◽  
Quality Health ◽  
Motor Apraxia

AbstractJoubert syndrome (JS) is a rare congenital, autosomal recessive disorder characterized by a distinctive brain malformation, developmental delay, ocular motor apraxia, breathing abnormalities, and high clinical and genetic heterogeneity. We are reporting three siblings with JS from consanguineous parents in Syria. Two of them had the same homozygous c.2172delA (p.Trp725Glyfs*) AHI1 mutation and the third was diagnosed prenatally with magnetic resonance imaging. This pathogenic variant is very rare and described in only a few cases in the literature. Multinational collaboration could be of benefit for the patients from undeveloped, low-income countries that have a low-quality health care system, especially for the diagnosis of rare diseases.

Reviewing the Development of Rural Finance in Vietnam

2013 ◽  
pp. 121-136
Author(s):  
Duong Pham Bao
Keyword(s):  
Low Income ◽  
Financial System ◽  
Low Income Countries ◽  
Supply Side ◽  
New Paradigm ◽  
Rural Finance ◽  
Market Mechanisms ◽  
Rural Credit ◽  
Rural Organizations ◽  
Doi Moi

The objective of this article is to review the development of the rural financial system in Vietnam in recent years, especially, after Doi moi. There are two opposite schools of thought in the literature on rural credit policies in developing countries. One is the conventional supply-side (government-led) approach while the other is called “a new paradigm” that emphasizes the importance of the viability of financial providers and the well functioning of rural credit markets. Conventional theories of rural finance contend that rural finance in low-income countries is generally accompanied by many failures. Contrary to these theories, rural finance in Vietnam does not encounter the above-mentioned failures so far. Up to the present time, it is progressing well. Using a supply-side approach, methodologically, this study reviews the development of the rural financial system in Vietnam. The significance of this study is to challenge the extreme view of dichotomizing between the old and the new credit paradigms. Analysis in this study contends that a rural financial market that, (1) is initiated and spurred by government; (2) operates principally under market mechanisms; and (3) is strongly supported by rural organizations (semi-formal/informal institutions) can progress stably and well. Therefore, the extremely dichotomizing approach must be avoided.

Abdominal Textiloma Mimicking as Left Colic Tumour: A Postoperative Complication Still Common in Low-Income Countries

EMJ Radiology ◽  
2020 ◽  
Keyword(s):  
Low Income ◽  
Early Stage ◽  
Low Income Countries ◽  
Fistula Formation ◽  
Emergency Laparotomy ◽  
Intermittent Fever ◽  
Gastrointestinal Complications ◽  
Surgical Safety ◽  
Surgical Teams ◽  
Safety Rules

Retained foreign bodies have become very rare in countries where the safety rules in the operating theatre are very rigorous and follow precise guidelines. There are low-income countries where hospital structures are precarious, in which the implementation of surgical safety rules has only been effective recently. Surgical teams in these countries are not yet well trained in the observance of the guidelines concerning swab count, meaning that textilomas are not uncommon. Abdominal textiloma may be asymptomatic, or present serious gastrointestinal complications such as bowel obstruction, perforation, or fistula formation because of misdiagnosis. It may mimic abscess formation in the early stage or soft tissue masses in the chronic stage. This case report presents a 27-year-old female who underwent an emergency laparotomy in a rural surgical centre for an ectopic pregnancy. Two months later, a swelling had appeared on the left side of her abdomen, gradually increasing in size, which was not very painful but caused digestive discomfort and asthenia. Intermittent fever was described and treated with antibiotics. The patient was referred to a better equipped centre to benefit from a CT scan. A textiloma was strongly suspected on the CT but a left colic mass was not excluded. Laparotomy confirmed the diagnosis of textiloma and the postoperative course was uneventful. Prevention rules must be strengthened in these countries where patients can hardly bear the costs of iterative surgeries for complications that are avoidable.

Assessment of knowledge and practice of vaccination of dogs against rabies by dog owners in Makurdi, Benue State, Nigeria

2020 ◽  
Vol 1 ◽  
pp. 5
Author(s):  
Audu Onyemocho ◽  
Agwa Moses ◽  
Aboh Kisani ◽  
Omole Namben Victoria ◽  
Anejo-Okopi Joseph
Keyword(s):  
Low Income ◽  
Life Time ◽  
Knowledge Score ◽  
Educational Status ◽  
Low Income Countries ◽  
Bivariate Analysis ◽  
Cross Sectional ◽  
Knowledge And Practice ◽  
Dog Owners ◽  
The Relationship

Objective: Rabies, one of the oldest and fatal infectious diseases known to human race, is transmitted by infected dogs. The global target of zero dog-mediated rabies human deaths has been set for 2030; however, the realization of this goal poses challenges in most low-income countries where rabies is endemic due to weak surveillance. Dogs have been increasingly deployed for domestic uses over the years, especially for security purposes. This study assessed the assessment of knowledge and practice of vaccination of dogs against rabies by dog owners. Materials and Methods: A cross-sectional community-based study was employed to study 400 dog owners in Makurdi metropolis through multistage sampling techniques. Sighting of valid dog vaccination card was used as criteria for current vaccination. Bivariate analysis was carried out to establish the relationship between the respondent knowledge of rabies and dog vaccination with significant value set at P < 0.05. Results: The mean age of the respondents was 31 (Â ± 0.8) years, majority of them had tertiary and secondary education (40.0% and 39.0%, respectively), 26.0% were traders, and 50.0% were married. Overall, 73.0% of the respondents had good knowledge score, 61.0% had seen at least a rabid dog in their life time, and 74.0% have a history of dog vaccination, but evidence of up to date vaccination of dogs by owners was seen in only 18.0% of all the vaccination cards sighted. The relationship between the educational status of the respondents, their knowledge score, and their dog vaccination was statistically significant (P < 0.05). Conclusion: Knowledge of rabies among dog owners in Makurdi was good, but the practice of dog vaccination was poor. Educational status was a good predictor of practice. Awareness campaign on dog vaccination should be strengthened and adequate measures should be put in place at the veterinary hospitals in Makurdi for vaccination of dogs.

Sign in / Sign up

Export Citation Format

Share Document