Geographic information systems and the environmental risk of schistosomiasis in Bahia, Brazil.

Abstract

Abstract. A geographic information system was constructed using maps of regional environmental features, Schistosoma mansoni prevalence in 30 representative municipalities, and snail distribution in Bahia, Brazil to study the spatial and temporal dynamics of infection and to identify environmental factors that influence the distribution of schistosomiasis. Results indicate that population density and the duration of annual dry period are the most important determinants of prevalence of schistosomiasis in the areas selected for study. Maximum rainfall, total precipitation during three consecutive months, annual maximum or minimum temperatures, and diurnal temperature difference were not shown to be significant factors influencing S. mansoni prevalence in local populations or distribution of snail hosts. Prevalence of the disease was highest in the coastal areas of the state. Higher prevalence tended to occur in areas with latossolo soil type and transitional vegetation.Schistosomiasis, which is caused by Schistosoma mansoni, was introduced into Brazil in the mid 1550s 1 and became established as a significant health problem in the endemic states of the northeast region of the country. Ecologic factors favorable to the intermediate snail hosts and the concentration of susceptible humans hosts living under substandard conditions have contributed to maintenance of the disease and expansion of the endemic area. 2 While spatial distribution and prevalence have remained constant in some regions since surveys done in the 1950s, outbreaks have been reported in regions previously considered free of schistosomiasis. Spread of the disease to newly settled areas is a major concern of the National Schistosomiasis Control Program.Studies done on rural communities in Bahia 3-5 have shown that the number, distribution, and rate of infection of the intermediate host Biomphalaria glabrata and contact with domestic water were key determinants of human infection prevalence and that snail populations responded to seasonal rainfall patterns, with an increase in reproduction during the period October through January and proportional decreases during months of drought. A study contrasting communities with high and low prevalence rates of S. mansoni in Sao Paulo State revealed that high altitude, low population density, high standards of sanitation, and limited numbers of breeding sites for B. tenagophila, the principal intermediate host in the Sao Paulo area, contributed to low rates of infection. 5 A knowledge of the factors contributing to the size and location of snail populations is pivotal to planning and implementing effective programs of suppression using molluscicides. Since the number of intermediate hosts, their concentration, and rate of infection may be functions of rainfall, vegetation, topography, soil type, and characteristics of water bodies, geographic information system (GIS) methods may be suitable for analysis of the spatial relationships of the environment, mollusk intermediate hosts, and schistosomiasis in specific...

Microgeographical patterns of schistosomiasis and water contact behavior; examples from Africa and Brazil

“…Thus, intensity of infection is influenced considerably by the frequency, duration and intensity of human contact with infective water. Spatial studies of schistosomiasis, snail intermediate hosts and water resources have been carried out at both the macrogeographical (world-wide, regional, national and district) (Hunter 1981, Doumenge 1987, Kloos et al 1988, Bavia et al 1994) and microgeographical (community) levels (Kloos et al 1983, Lima e Costa et al 1985, Kloetzel 1989, Barreto 1991. Although they use data of different levels of aggregation and specificity, these two types of study can complement each other.…”

Assessment of control and epidemiologic details of the schistosomiasis mansoni in Bananal, São Paulo, Brazil

“…The use of the geographical information system -or geoprocessing -in planning the fight against and evaluation of the risks of the spread of schistosomiasis has also been the subject of studies in Brazil [26][27][28][29][30] . In general, the results of these studies bring together such diversified parameters such as the characteristics of the vegetation, temperature changes, availability of water collections, occurrence of species of intermediate hosts, as well as the distribution of cases and foci.…”

Mapping and modelling neglected tropical diseases and poverty in Latin America and the Caribbean

“…Malaria and schistosomiasis, for example, are both environmentally sensitive, vector-borne diseases, which provide striking examples of the steady progress and increasing sophistication in the geospatial health arena (Cross et al, 1984;Bavia et al, 1999;Craig et al, 1999;Clements et al, 2006;Hay et al, 2009;Thomson et al, 2010;Zhou et al, 2010). In 1995, the NASA Ames Center for Health Applications of Aerospace Related Technologies (CHAART) was established by Byron Wood and Louisa Beck, who set about promoting applications in health by way of inhouse research, a small-grants programme and widely publicizing the medical potential of the new technolo-gies through symposia and workshops Wood et al, 2000).…”