Associations between patterns of human intestinal schistosomiasis and snail and mammal species richness in Uganda: can we detect a decoy effect?

Anna-Sofie Stensgaard,Carsten Rahbek,Thomas K Kristensen,Narcis B Kabatereine,Aslak Jørgensen

doi:10.21425/f58321748

Abstract

In recent years, ecological research has suggested several mechanisms by which biodiversity might affect the risk of acquiring infectious diseases (i.e., the decoy, dilution or amplification effects), but the topic remains controversial. While many experimental studies suggest a negative relationship between biodiversity and disease, this relationship is inherently complex, and might be negative, positive or neutral depending on the geographical scale and ecological context. Here, applying a macroecological approach, we look for associations between diversity and disease by comparing the distribution of human schistosomiasis and biogeographical patterns of freshwater snail and mammal species richness in Uganda. We found that the association between estimated snail richness and human infection was best described by a negative correlation in non-spatial bi- and multivariate logistic mixed effect models. However, this association lost significance after the inclusion of a spatial component in a full geostatistical model, highlighting the importance of accounting for spatial correlation to obtain more precise parameter estimates. Furthermore, we found no significant relationships between mammal richness and schistosomiasis risk. We discuss the limitations of the data and methods used to test the decoy hypothesis for schistosomiasis, and highlight key future research directions that can facilitate more powerful tests of the decoy effect in snail-borne infections, at geographical scales that are relevant for public health and conservation.

Highlights

In recent years there has been a growing interest in how changes in community structure and loss of biodiversity influence parasite transmission and infection risk in multi-species assemblages (e.g., Keesing et al 2010, Civitello et al 2015, Johnson et al 2015)
We focus on Chao2 as the measure of snail richness
There was no significant association between mammal richness and infection status, but mammal richness was retained for multivariate modelling for comparison with snail richness

Summary

Introduction

In recent years there has been a growing interest in how changes in community structure and loss of biodiversity influence parasite transmission and infection risk in multi-species assemblages (e.g., Keesing et al 2010, Civitello et al 2015, Johnson et al 2015). The generality of the dilution effect remains fiercely debated (Randolph and Dobson 2012, Salkeld et al 2013, Wood and Lafferty 2013, Wood et al 2014): Critics argue that the direction of such a relationship is just as likely to be neutral or positive (referred to as an amplification effect) and of varying magnitude, depending on the disease system in question, the ecological context and the geographical scale of study (Wood et al 2014). Due to a shortage of vital empirical data, the understanding of the extent to which patterns of biodiversity influence different disease systems across spatial scales is still very limited (Hough 2014, Johnson et al 2015)

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Results

Conclusion