Mapping the Risk of Soil-Transmitted Helminthic Infections in the Philippines.

Ricardo J Soares Magalhães,Laith Yakob,Darren J Gray,Archie C A Clements,Ofelia Saniel,Lydia Leonardo,Gail M Williams,Donald P Mcmanus,Pilarita Rivera,Hélène Carabin,Kate Halton,Maria S Salamat,Stephen T Mcgarvey,Leda Hernandez,Stefanie Knopp

doi:10.1371/journal.pntd.0003915

Abstract

BackgroundIn order to increase the efficient allocation of soil-transmitted helminth (STH) disease control resources in the Philippines, we aimed to describe for the first time the spatial variation in the prevalence of A. lumbricoides, T. trichiura and hookworm across the country, quantify the association between the physical environment and spatial variation of STH infection and develop predictive risk maps for each infection.Methodology/Principal FindingsData on STH infection from 35,573 individuals across the country were geolocated at the barangay level and included in the analysis. The analysis was stratified geographically in two major regions: 1) Luzon and the Visayas and 2) Mindanao. Bayesian geostatistical models of STH prevalence were developed, including age and sex of individuals and environmental variables (rainfall, land surface temperature and distance to inland water bodies) as predictors, and diagnostic uncertainty was incorporated. The role of environmental variables was different between regions of the Philippines. This analysis revealed that while A. lumbricoides and T. trichiura infections were widespread and highly endemic, hookworm infections were more circumscribed to smaller foci in the Visayas and Mindanao.Conclusions/SignificanceThis analysis revealed significant spatial variation in STH infection prevalence within provinces of the Philippines. This suggests that a spatially targeted approach to STH interventions, including mass drug administration, is warranted. When financially possible, additional STH surveys should be prioritized to high-risk areas identified by our study in Luzon.

Highlights

Soil-transmitted helminth (STH) infections are believed to affect two billion people worldwide, equating to approximately one-third of the world’s population
In order to increase the efficient allocation of soil-transmitted helminth (STH) disease control resources in the Philippines, we aimed to describe for the first time the spatial variation in the prevalence of A. lumbricoides, T. trichiura and hookworm across the country, quantify the association between the physical environment and spatial variation of STH infection and develop predictive risk maps for each infection
The role of environmental variables was different between regions of the Philippines. This analysis revealed that while A. lumbricoides and T. trichiura infections were widespread and highly endemic, hookworm infections were more circumscribed to smaller foci in the Visayas and Mindanao

Summary

Introduction

Soil-transmitted helminth (STH) infections are believed to affect two billion people worldwide, equating to approximately one-third of the world’s population. STH infections in children have been linked to anaemia and impaired cognitive and physical development [3,4,5]. These STH species are widely distributed in tropical and subtropical areas [6]. In order to increase the efficient allocation of soil-transmitted helminth (STH) disease control resources in the Philippines, we aimed to describe for the first time the spatial variation in the prevalence of A. lumbricoides, T. trichiura and hookworm across the country, quantify the association between the physical environment and spatial variation of STH infection and develop predictive risk maps for each infection

Objectives

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Discussion

Conclusion