Modelling the spatial and seasonal distribution of suitable habitats of schistosomiasis intermediate host snails using Maxent in Ndumo area, KwaZulu-Natal Province, South Africa.

Tawanda Manyangadze,Moses John Chimbari,Samson Mukaratirwa,Pietro Ceccato,Michael Gebreslasie

doi:10.1186/s13071-016-1834-5

Tawanda Manyangadze, Moses John Chimbari + Show 3 more

Open Access

https://doi.org/10.1186/s13071-016-1834-5

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Abstract

BackgroundSchistosomiasis is a snail-borne disease endemic in sub-Saharan Africa transmitted by freshwater snails. The distribution of schistosomiasis coincides with that of the intermediate hosts as determined by climatic and environmental factors. The aim of this paper was to model the spatial and seasonal distribution of suitable habitats for Bulinus globosus and Biomphalaria pfeifferi snail species (intermediate hosts for Schistosoma haematobium and Schistosoma mansoni, respectively) in the Ndumo area of uMkhanyakude district, South Africa.MethodsMaximum Entropy (Maxent) modelling technique was used to predict the distribution of suitable habitats for B. globosus and B. pfeifferi using presence-only datasets with ≥ 5 and ≤ 12 sampling points in different seasons. Precipitation, maximum and minimum temperatures, Normalised Difference Vegetation Index (NDVI), Normalised Difference Water Index (NDWI), pH, slope and Enhanced Vegetation Index (EVI) were the background variables in the Maxent models. The models were validated using the area under the curve (AUC) and omission rate.ResultsThe predicted suitable habitats for intermediate snail hosts varied with seasons. The AUC for models in all seasons ranged from 0.71 to 1 and the prediction rates were between 0.8 and 0.9. Although B. globosus was found at more localities in the Ndumo area, there was also evidence of cohabiting with B. pfiefferi at some of the locations. NDWI had significant contribution to the models in all seasons.ConclusionThe Maxent model is robust in snail habitat suitability modelling even with small dataset of presence-only sampling sites. Application of the methods and design used in this study may be useful in developing a control and management programme for schistosomiasis in the Ndumo area.

Highlights

Schistosomiasis is a snail-borne disease endemic in sub-Saharan Africa transmitted by freshwater snails
In this study we considered these factors at 2 levels: annual averages and seasonal averages to model the variation of suitable habitats of the host snails at micro-geographical scale
This study intended to model the spatial distribution of the suitable habitats for B. globosus and B. pfeifferi at a micro-geographical scale

Summary

Introduction

Schistosomiasis is a snail-borne disease endemic in sub-Saharan Africa transmitted by freshwater snails. The population dynamics of the intermediate snail hosts and parasite transmission patterns in situ are still to be adequately studied [4]. Even with inexpensive and effective anthelminthic medication (Praziquantel) the knowledge of the local dynamics of snail populations is still important for timing of mass drug administration, the global strategy endorsed by the World Health Organization [13]. This will help to follow the periods when re-infection is very low [14,15,16,17] so as to reduce the chances of reinfection. Understanding the dynamics of transmission of schistosomiasis could help to identify hot spots where transmission may be intense and build towards effective local intervention programmes

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