BJRP 011008

Spatio-temporal dynamics, risk factors and burden estimates of neglected tropical diseases in Brazil


Background:  There is a growing interest in the scientific community, philanthropic organizations and Ministries of Health to control and eventually eliminate neglected tropical diseases (NTDs). Control efforts require reliable baseline maps of the geographical distribution of NTDs and the number of infected individuals, including underlying risk factors, so that interventions can be focused to high-risk communities to enhance cost-effectiveness. In the Americas, Brazil accounts for the largest burden of NTDs with approximately 40 million individuals, mainly the rural poor, suffering from at least one and often multiple NTDs concurrently. However, apart from a few local studies which looked at the disease distribution using mainly exploratory tools, nationwide high-spatial resolution maps and assessment of the diseases determinants taking into account their complex interrelations to demography, ecology and socio-economy are not available. The proposed project builds on a 10-month consultancy the Swiss Tropical and Public Health Institute (Swiss TPH) in Basel, Switzerland and the University of Bahia in Brazil have been granted by the Pan America Health Organization (PAHO) towards the end of 2009 to produce maps and burden estimates of NTDs in the Americas at the first administrative level. An important epidemiological feature of NTDs is their focal distribution, and hence, assuming uniformity of the risk over broad areas results in non-informative and often erroneous estimates. There is a pressing need to estimate the distribution of NTDs taking into account their focality. Furthermore, there is need to develop data-driven spatio-temporal statistical and mathematical models to study not only the spatial distribution of NTDs, but also their evolution over time taking into account on-going interventions and other disease exposures for an integrated control of NTDs in Brazil and elsewhere in the humid tropics.

Goal and specific objectives:  The overarching goal of this joint research project (JPR) is to assess the distribution and the spatio-temporal dynamics of NTDs in Brazil. We will pursue five specific objectives: (i) to assess the contribution of demographic (including migration), climatic, environmental, socio-economic and health systems-related determinants on the geographical distribution of NTDs (i.e. schistosomiasis, soil-transmitted helminthiasis, Chagas disease, leishmaniasis, lymphatic filariasis and leprosy) in Brazil; (ii) to estimate and obtain nationwide high-spatial resolution maps of the disease burden (transmission risk, number of infected people, and estimates of disability-adjusted life years (DALYs) lost); (iii) to generate high-spatial resolution maps of the burden of selected co-infections and co-morbidities; (iv) to assess changes of the disease distribution over time and space; and (v) to explore the potential of statistical models to reliably forecast incidence and disease burden in the future.

Methods of investigation:  We will employ and further develop innovative data-driven Bayesian, including binomial, negative binomial and zero-inflated (a) geostatistical, non-stationary models collected over large number of locations, (b) shared component models for a joint spatial analysis of selected disease co-infections, (c) geospatial-temporal models for estimating prevalence and incidence data, and (d) mathematical transmission models to standardise age-heterogeneous historical survey data. The models will be fitted (i) using Markov chain Monte Carlo (MCMC) and reversible jump (RJMCMC) simulation algorithms, and (ii) analysing spatially structured databases from historical prevalence and incidence data available in the Federal Ministry of Health or extracted from the peer-reviewed literature.

Time scale:  This is a 2-year project, commenting in October 2010 and ending in September 2012.

Significance:  This proposed JRP will (i) generate up-to-date burden estimates and country-wide maps of NTDs in Brazil and related co-infections/co-morbidities at high spatial resolution. These maps will be of value in gauging needs of control programmes, and can serve as a benchmark for estimating the effectiveness of national control programmes; (ii) deepen our understanding of the demographic, climatic, environmental, socio-economic, health systems-related factors and their relative contribution to the transmission of NTDs, which will be of value for health planning and resource allocation, since it will make possible to control the diseases not only by large-scale administration of drugs, but through reducing exposures; (iii) determine the spatio-temporal dynamics of the distribution of NTDs, the factors related to them and project the disease progression; (iv) enhance data-driven rigorous statistical methodologies for modeling the spatio-temporal dynamics of NTDs, which will enable not only risk factor analysis and mapping of the selected NTDs in Brazil, but also for other diseases and regions (i.e. Latin America and Caribbean); (v) develop an open-access database and cataloguing of historical data pertaining to NTDs and interventions in Brazil available to researchers for testing different models and methodologies to address similar epidemiological questions. The project will strengthen and expand established collaborations between the Swiss TPH and Brazilian partner institutions, and train the next generation of spatio-temporal modelers and disease mapping experts in Brazil.