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Modelling the geographical distribution of soil-transmitted helminth infections in Bolivia

Frédérique Chammartin12, Ronaldo GC Scholte12, John B Malone3, Mara E Bavia4, Prixia Nieto3, Jürg Utzinger12 and Penelope Vounatsou12*

Author Affiliations

1 Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, , CH-4002 Basel, Switzerland

2 University of Basel, P.O. Box, , CH-4003 Basel, Switzerland

3 School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, 70803, USA

4 Preventive Medicine Department, Federal University of Bahia, Salvador, Bahia, 40110-060, Brazil

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Parasites & Vectors 2013, 6:152  doi:10.1186/1756-3305-6-152

Published: 25 May 2013

Abstract

Background

The prevalence of infection with the three common soil-transmitted helminths (i.e. Ascaris lumbricoides, Trichuris trichiura, and hookworm) in Bolivia is among the highest in Latin America. However, the spatial distribution and burden of soil-transmitted helminthiasis are poorly documented.

Methods

We analysed historical survey data using Bayesian geostatistical models to identify determinants of the distribution of soil-transmitted helminth infections, predict the geographical distribution of infection risk, and assess treatment needs and costs in the frame of preventive chemotherapy. Rigorous geostatistical variable selection identified the most important predictors of A. lumbricoides, T. trichiura, and hookworm transmission.

Results

Results show that precipitation during the wettest quarter above 400 mm favours the distribution of A. lumbricoides. Altitude has a negative effect on T. trichiura. Hookworm is sensitive to temperature during the coldest month. We estimate that 38.0%, 19.3%, and 11.4% of the Bolivian population is infected with A. lumbricoides, T. trichiura, and hookworm, respectively. Assuming independence of the three infections, 48.4% of the population is infected with any soil-transmitted helminth. Empirical-based estimates, according to treatment recommendations by the World Health Organization, suggest a total of 2.9 million annualised treatments for the control of soil-transmitted helminthiasis in Bolivia.

Conclusions

We provide estimates of soil-transmitted helminth infections in Bolivia based on high-resolution spatial prediction and an innovative variable selection approach. However, the scarcity of the data suggests that a national survey is required for more accurate mapping that will govern spatial targeting of soil-transmitted helminthiasis control.

Keywords:
Bayesian modelling; Bolivia; Geostatistical variable selection; Mapping; Soil-transmitted helminths