Abstract
BackgroundIn Timor-Leste there have been intermittent and ineffective soil-transmitted helminth (STH) deworming programs since 2004. In a resource-constrained setting, having information on the geographic distribution of STH can aid in prioritising high risk communities for intervention. This study aimed to quantify the environmental risk factors for STH infection and to produce a risk map of STH in Manufahi district, Timor-Leste.Methodology/Principal findingsGeoreferenced cross-sectional data and stool samples were obtained from 2,194 participants in 606 households in 24 villages in the Manufahi District as part of cross sectional surveys done in the context of the “WASH for Worms” randomised controlled trial. Infection status was determined for Ascaris lumbricoides and Necator americanus using real-time quantitative polymerase chain reaction. Baseline infection data were linked to environmental data obtained for each household. Univariable and multivariable multilevel mixed-effects logistic regression analysis with random effects at the village and household level were conducted, with all models adjusted for age and sex. For A. lumbricoides, being a school-aged child increased the odds of infection, whilst higher temperatures in the coolest quarter of the year, alkaline soils, clay loam/loam soils and woody savannas around households were associated with decreased infection odds. For N. americanus, greater precipitation in the driest month, higher average enhanced vegetation index, age and sandy loam soils increased infection odds, whereas being female and living at higher elevations decreased the odds of infection. Predictive risk maps generated for Manufahi based upon these final models highlight the high predicted risk of N. americanus infection across the district and the more focal nature of A. lumbricoides infection. The predicted risk of any STH infection is high across the entire district.Conclusions/SignificanceThe widespread predicted risk of any STH infection in 6 to 18 year olds provides strong evidence to support strategies for control across the entire geographical area. As few studies include soil texture and pH in their analysis, this study adds to a growing body of evidence suggesting these factors influence STH infection distribution. This study also further supports that A. lumbricoides prefers acidic soils, highlighting a potential relatively unexplored avenue for control.Trial registrationClinicalTrials.gov ACTRN12614000680662.
Highlights
In this study we predicted the risk of Ascaris lumbricoides, Necator americanus and any soil-transmitted helminth (STH) infection in the Manufahi district of Timor-Leste, providing the first available risk maps for STH infection in any part of the country
We assessed the relationship between selected environmental factors and STH infection to create multivariable models accounting for potential clustering of infections in villages and households
We found that the predicted risk of infection with N. americanus in the age group older than 18 years of age and with any STH in 6–18 year olds was high and widespread across Manufahi, supporting the need for control strategies across the entire geographical region
Summary
Soil-transmitted helminth (STH) infections are predominantly a disease of poverty, typically prevalent in poor tropical and subtropical regions. [1] In 2010, the four main species of human STH were estimated to infect 1.5 billion people worldwide; with whipworm (Trichuris trichiura), roundworm (Ascaris lumbricoides) and the two main species of hookworm (Ancylostoma duodenale and Necator americanus) respectively infecting 464.6 million, 819.0 million, and 438.9 million people. [2] The majority of STH infections are insidious for hosts living in impoverished conditions, and have a demonstrable impact on an individual’s health and wellbeing. [1, 3] A. lumbricoides and T. trichiura are thought to contribute to malnutrition, whereas hookworm and T. trichiura infections have been associated with iron-deficiency anaemia. [4, 5] All four main human STH species have been associated with impaired childhood growth. [5,6,7] Anaemia and malnutrition may have a negative long-term impact on an individual’s health and productivity, [6, 7] with resulting economic ramifications contributing to the cycle of poverty. [3] To reduce the impact of STH on communities, comprehensive control strategies are required. An impediment to implementing cost-effective control programs is a lack of accurate information detailing the geographic distribution of STH infections. [9] Over the past two decades, geographic information systems (GIS) coupled with remotely sensed environmental data have been used to identify areas of high STH infection risk in several countries, [10,11,12,13,14,15] allowing governments to develop cost-effective targeted STH control strategies. [19] Given the limited resources available in Timor-Leste, cost-effective methods to identify populations at high risk of STH infections are needed. [19] Using this cross-sectional data, this study aimed to describe and predict the distribution of STH infection in Manufahi district using environmental variables. This study aimed to quantify the environmental risk factors for STH infection and to produce a risk map of STH in Manufahi district, Timor-Leste
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