Spatial analysis and risk mapping of soil-transmitted helminth infections in Brazil, using Bayesian geostatistical models

Abstract

Abstract. Soil-transmitted helminths (Ascaris lumbricoides, Trichuris trichiura and hookworm) negatively impact the health and wellbeing of hundreds of millions of people, particularly in tropical and subtropical countries, including Brazil. Reliable maps of the spatial distribution and estimates of the number of infected people are required for the control and eventual elimination of soil-transmitted helminthiasis. We used advanced Bayesian geostatistical modelling, coupled with geographical information systems and remote sensing to visualize the distribution of the three soil-transmitted helminth species in Brazil. Remotely sensed climatic and environmental data, along with socioeconomic variables from readily available databases were employed as predictors. Our models provided mean prevalence estimates for A. lumbricoides, T. trichiura and hookworm of 15.6%, 10.1% and 2.5%, respectively. By considering infection risk and population numbers at the unit of the municipality, we estimate that 29.7 million Brazilians are infected with A. lumbricoides, 19.2 million with T. trichiura and 4.7 million with hookworm. Our model-based maps identified important risk factors related to the transmission of soiltransmitted helminths and confirm that environmental variables are closely associated with indices of poverty. Our smoothed risk maps, including uncertainty, highlight areas where soil-transmitted helminthiasis control interventions are most urgently required, namely in the North and along most of the coastal areas of Brazil. We believe that our predictive risk maps are useful for disease control managers for prioritising control interventions and for providing a tool for more efficient surveillance-response mechanisms.

Trichuris trichiura infection and its relation to environmental factors in Mbeya region, Tanzania: A cross-sectional, population-based study

“…The univariable inverse association of LST day with infection is consistent with previous research [31, 32]. The likely explanation is that higher soil temperatures lead to desiccation of the soil and the parasite eggs.…”

“…[31] found a trend towards an inverse association between infection and rainfall, whereas Scholte et al . [32] found rainfall to be a risk factor for T . trichiura infection.…”

“…trichiura infection is higher close to water bodies [30–32, 34]. This could be related to low altitude, moderated temperatures and high soil moisture near water.…”

“…trichiura infection was limited to the vicinity of Lake Nyasa in Kyela. The affinity to water was not only found in Sub-Saharan Africa [30, 31, 34], but also in the Americas [32]. …”

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

“…These models have been widely used in assessing the relationship between helminth infection with demographic, environmental, and socioeconomic predictors, at sub-national [11,18], national [19], or regional scales [13,20,21]. In the Americas, high resolution, geostatistical, model-based risk estimates have been obtained for the whole continent [22] as well as for Brazil [23]. A key issue in geostatistical modelling is the selection of the predictors.…”