Risk profiling of soil-transmitted helminth infection and estimated number of infected people in South Asia: A systematic review and Bayesian geostatistical Analysis

Abstract

Background In South Asia, hundreds of millions of people are infected with soil-transmitted helminths ( Ascaris lumbricoides , hookworm, and Trichuris trichiura ). However, high-resolution risk profiles and the estimated number of people infected have yet to be determined. In turn, such information will assist control programs to identify priority areas for allocation of scarce resource for the control of soil-transmitted helminth infection. Methodology We pursued a systematic review to identify prevalence surveys pertaining to soil-transmitted helminth infections in four mainland countries (i.e., Bangladesh, India, Nepal, and Pakistan) of South Asia. PubMed and ISI Web of Science were searched from inception to April 25, 2019, without restriction of language, study design, and survey date. We utilized Bayesian geostatistical models to identify environmental and socioeconomic predictors, and to estimate infection risk at high spatial resolution across the study region. Principal findings A total of 536, 490, and 410 georeferenced surveys were identified for A . lumbricoides , hookworm, and T . trichiura , respectively. We estimate that 361 million people (95% Bayesian credible interval (BCI) 331–395 million), approximately one-quarter of the South Asia population, was infected with at least one soil-transmitted helminth species in 2015. A . lumbricoides was the predominant species. Moderate to high prevalence (>20%) of any soil-transmitted helminth infection was predicted in the northeastern part and some northern areas of the study region, as well as the southern coastal areas of India. The annual treatment needs for the school-age population requiring preventive chemotherapy was estimated at 165 million doses (95% BCI: 146–185 million). Conclusions/significance Our risk maps provide an overview of the geographic distribution of soil-transmitted helminth infection in four mainland countries of South Asia and highlight the need for up-to-date surveys to accurately evaluate the disease burden in the region.

Model-based spatial-temporal mapping of opisthorchiasis in endemic countries of Southeast Asia

“…HII, a measure of human direct influence on ecosystems (Sanderson, et al,2002), showed a positive relationship with O. viverrini infection risk. A similar association has been found on HII and A. lumbricoides infection in South Asia (Lai, et al,2019). People living in areas with a longer distance to the nearest open water bodies tended to have lower risk, consistent with the previous finding (Forrer, et al,2012).…”

“…The coordinates of the survey locations were obtained from Google Maps (https://www.google.com/maps/). Considering that areas are much smaller of ADM2 or ADM3, compared to that of ADM1, we treated surveys aggregated in ADM2 or ADM3 as point-level georeferenced at division centroids referring to previous studies (Lai, et al,2019), while surveys aggregated over ADM1 as area-level, in order to avoid large uncertainty in the later geostatistical analysis.…”

Elimination of STH morbidity in Zimbabwe: Results of 6 years of deworming intervention for school-age children

“…First, we assembled a set of environmental, socioeconomic and physical covariates for the analysis including: proportion of open defecation in 2011 and 2015, elevation, enhanced vegetation index (EVI), normalized difference vegetation index (NDVI), rainfall, soil PH, soil moisture, composition of the soil, night light emission, land surface temperature for day and night and number of MDA rounds. These covariates were chosen because they are either associated with the prevalence of any of the STH parasites or serve as a proxy for other factors that are known to drive the prevalence of any of the STH parasites [ 15 ]. The complete list of covariates and their values in the binomial geostatistical model are provided in supplementary material S1 Table (baseline) and S2 Table (impact assessment).…”

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“…Significant worldwide reductions in prevalence of Ascaris (-25.5% since 1990) have been estimated, but these reductions have been modest for Trichuris (-11.6%) and even smaller for hookworm (-5.1%) [2]. In more recent estimates (2015), 258 million (or 1 in 5) individuals in India are estimated to be infected with STH, with 148 million Ascaris, 109 million hookworm and 41 million Trichuris infections, indicating a lower prevalence of Ascaris and Trichuris, but a higher prevalence of hookworm than previous reports [3]. Moderate-and heavy-intensity (MHI) hookworm infections are (dw3data@uw.edu) for researchers who meet the criteria for access to these data.…”