Socioeconomic determinants of schistosomiasis in a poor rural area in Brazil
Introduction
There is considerable evidence that socioeconomic conditions are often strongly associated with schistosomiasis occurrence. This relationship was first described in detail by Farooq et al. (1966) in Egypt and since then by studies in different endemic areas (Rosenfield, 1990, Yi-Xin and Manderson, 2005). In Brazil, the role of socioeconomic factors in Schistosoma mansoni transmission has been examined by studies in rural areas (Coura-Filho et al., 1994, Lima e Costa et al., 1991, Silva et al., 1997) and urban (Barreto, 1991, Kloetzel, 1989, Lima e Costa et al., 1987, Ximenes et al., 2003). However, only Ximenes et al. (2003) studied the relationship between socioeconomic determinants and schistosomiasis distribution in depth, using non-causal determinism, which posits that socioeconomic conditions determine and operate through various conditioning factors, or intermediate mechanisms, not necessarily in a causal manner. They found a strong relationship between socioeconomic variables and schistosomiasis in a town in northeast Brazil, but their findings are not applicable to rural areas, where the generally weaker socioeconomic differentiation and more widespread schistosomiasis risk present a different epidemiological setting. Socioeconomic studies are still called for as Brazil is still in need of an adaptable national schistosomiasis control methodology that considers local differences in disease ecology (WHO, 2001).
The study area, Virgem das Graças, is located in the S. mansoni-endemic area of northern Minas Gerais State and shares many physical and socioeconomic environmental features with the larger endemic region of northeastern Brazil, of which the study area forms part of the southern fringe. They include a semiarid climate with unreliable rainfall, marginalized subsistence farming, widespread poverty, high rates of rural–urban migration, and many communities with hyperendemic schistosomiasis. Partly due to its isolation, the Virgem das Graças population had never been treated for schistosomiasis by the government program. The hypothesis of this study is that the distribution of schistosomiasis in the Virgem das Graças population is determined by socioeconomic factors rather than occurring at random. Due to the high degree of household aggregation of schistosomiasis reported by Bethony et al. (2001) from a nearby rural study area and by Ximenes et al. (2003) in a town in northeastern Brazil, the role the household as a social organization and in economic decision making (Berman et al., 1994, Kroeger, 1985), particular emphasis in this study was given to the household level.
This study constitutes part of a broader epidemiological and immunological project. Malacological surveys revealed the high transmission potential of the 11 types of natural and manmade snail habitats studied by Kloos et al. (2004). Concomitant water contact studies carried out in three representative localities in the study area that used multiple methodologies indicate high exposure risk levels for the study population (Kloos et al., 2006).
Section snippets
Study area, economy and population
Virgem das Graças is a 60 km2 large rural area of Ponto dos Volantes Municipality, located in the Jequitinhonha Valley in northern Minas Gerais State, 120 km north of the town of Teófilo Otoni. According to our census survey in 2001, 589 people (48.2% males and 51.8% females) lived in the study area in 141 households. More than one-third of both the male and female population were 14 years old and younger (Table 1), indicating a high dependency ratio. Sixty-two percent of the population had been
Results
Of the 559 study subjects in the 136 households, 47.2% were males and 52.8% females. The population age ranged from 2 to 95 years (mean 30.9, S.D. 22.4, and median 24.0 years). The extreme age groups, <14 years and >65 years, represent 32.6% and 8.1% of the entire population, respectively. No significant differences were found between the responses of male and female heads.
The overall geometric mean egg count was 52.3 eggs per gram of feces, while the overall prevalence of infection was 58.7%.
Discussion
This study in an impoverished rural area within the region of high endemicity for schistosomiasis in Brazil shows a weak to moderate relationship between most socioeconomic indicators and infection. Education of head of household, household possessions, and number of persons per room were the major socioeconomic predictors of schistosomiasis occurrence and occupation of head of household became marginally significant in the multivariable model when included with education. The association of
Acknowledgements
This study received financial support from a Fogarty International Center Training Grant (1D43TW006580), Conselho de Desenvolvimento Tecnológico e Científico/CNPQ, Fundação de Amparo a Pesquisa do Estado de Minas Gerais/FAPEMIG, and the National Institutes of Health (NIH-ICIDR Grant A145451). Sara Crawford's research was supported in part by an appointment to the Research Participation Program at the Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division
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2016, Acta TropicaCitation Excerpt :Prevalence and intensity of infection were higher among schoolchildren resident in the rural area and in the later years of schooling, following a profile commonly found in the endemic areas of Minas Gerais (Massara et al., 2004; Enk et al., 2010). Schistosomiasis tend to be more frequent among residents of rural areas, where environmental sanitation and water supply conditions are generally more precarious and where there is greater proximity and contact between the local population and foci of transmission (Gazzinelli et al., 2009). Higher intensity of infection found here among male schoolchildren can be explained by the fact that the boys engage in more water contact than the girls, both in leisure activities, such as fishing and swimming, and in occupational activities, with many helping out with farm work in activities that involve more frequent and/or longer exposure to infection.