Research Article: Mapping the Risk of Soil-Transmitted Helminthic Infections in the Philippines

Date Published: September 14, 2015

Publisher: Public Library of Science

Author(s): Ricardo J. Soares Magalhães, Maria S. Salamat, Lydia Leonardo, Darren J. Gray, Hélène Carabin, Kate Halton, Donald P. McManus, Gail M. Williams, Pilarita Rivera, Ofelia Saniel, Leda Hernandez, Laith Yakob, Stephen T. McGarvey, Archie C. A. Clements, Stefanie Knopp.

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.

Partial Text: Soil-transmitted helminth (STH) infections are believed to affect two billion people worldwide, equating to approximately one-third of the world’s population. Ascaris lumbricoides, Trichuris trichiura and the hookworms Necator americanus and Ancylostoma duodenale, are the species responsible for most of these infections [1]. The infective stages of these parasites are found in fecally contaminated environments, which means that a lack of clean water, sanitation and hygiene (WASH) contribute considerably to their transmission [2].

This study represents the first to use model-based geostatistical predictive methods for STHs in a Southeast Asian context and demonstrates that STH infection prevalence in the Philippines is spatially variable. This study also shows that the predicted geographical distribution of A. lumbricoides and T. trichiura infection prevalence is more widespread than hookworm infection and in many areas the two species overlap. Finally, it indicates that the measured environmental factors are more strongly associated with the prevalence of these parasites in Mindanao than in Luzon and the Visayas.



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