Identification of factors and groups at risk of infection with Schistosoma mansoni: a strategy for the implementation of control measures?

Abstract

A fourteen year schistosomiasis control program in Peri-Peri (Capim Branco, MG) reduced prevalence from 43.5 to 4.4%; incidence from 19.0 to 2.9%, the geometric mean of the number of eggs from 281 to 87 and the level of the hepatoesplenic form cases from 5.9 to 0.0%. In 1991, three years after the interruption of the program, the prevalence had risen to 19.6%. The district consists of Barbosa (a rural area) and Peri-Peri itself (an urban area). In 1991, the prevalence in the two areas was 28.4% and 16.0% respectively. A multivariate analysis of risk factors for schistosomiasis indicated the domestic agricultural activity with population attributive risk (PAR) of 29.82%, the distance (< 10 m) from home to water source (PAR = 25.93%) and weekly fishing (PAR = 17.21%) as being responsible for infections in the rural area. The recommended control measures for this area are non-manual irrigation and removal of homes to more than ten meters from irrigation ditches. In the urban area, it was observed that swimming at weekly intervals (PAR = 20.71%), daily domestic agricultural activity (PAR = 4.07%) and the absence of drinking water in the home (PAR=4.29%) were responsible for infections. Thus, in the urban area the recommended control measures are the substitution of manual irrigation with an irrigation method that avoids contact with water, the creation of leisure options of the population and the provision of a domestic water supply. The authors call attention to the need for the efficacy of multivariate analysis of risk factors to be evaluated for schistosomiasis prior to its large scale use as a indicator of the control measures to be implemented.

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

“…Results show that the water contact patterns in Nova União are more complex than indicated by earlier studies using the interview method exclusively (Lima e Costa et al 1991, Coura-Filho et al 1994) for five reasons: (1) most households lacking a water supply obtained most or all their water from neighbors or relatives free of charge; they used the streams mainly for washing clothes and utensils; (2) eleven households with their own supply used the streams for domestic activities, mainly for washing clothes and utensils, and eight households used the wells, springs and piped outlets of other households, mainly because they preferred their water for cooking, drinking or other purposes or because their own supplies were inadequate; (3) all the households lacking their own supply or those with a supply and borrowing from other households were located on the slope away from the stream, where wells yielded less water and its quality was inferior (salty) to that of sources along the stream, indicating the importance of the hydrological environment in water use (Fig. 11); (4) the number of water contacts, particularly contacts for washing clothes and utensils at the distant stream sites decreased by more than 30% during the rainy season (February-March), when the streams carried large amounts of soil; and (5) the eight households which either constructed new wells, laundry sites, latrines and showers or installed an electric pump in their well during the 1-year study period increased their use of well water and de- creased the use of the streams showing a dynamic water use pattern.…”

Socioeconomic studies of schistosomiasis in Brazil: A review

“…Our preliminary review of the literature indicated that the great environmental, socioeconomic, cultural and epidemiological heterogenicity of Brazil renders the results of analyses of the relative importance of most individual factors (aside from the well researched water supply, sanitation, and education and parameters) in schistosomiasis distribution too inconclusive to support policy. Nearly all investigators, although using different study designs, sampling procedures (mostly random sampling without cluster sampling) and statistical methods (multivariate regression, with some supplementary parametric and non-parametric tests) but practically all using the Kato-Katz (Katz et al 1972) parasitological method and studying rural and urban areas in different parts of Brazil, arrived at similar conclusions: Agricultural and fishing activities were significantly correlated with S. mansoni prevalence and intensity of infection in most all rural communities (Coura-Filho et al, 1994; Silva et al, 1997; Lima e Costa et al, 1998; Bethony et al, 2004; Disch et al, 2002). In addition, bathing in and domestic contacts with streams (Lima e Costa et al, 1987; Silva et al, 1997; Bethony et al, 2004), poor quality housing (Lima e Costa et al 1991; Gazzinelli et al, 2006), absence of piped water (Lima e Costa et al, 1987; Coura-Filho et al, 1996; Gazzinelli et al, 2001), latrines and shower, low level of education, and being born in a rural area (Bethony et al, 2001) were all found to be significantly associated with S. mansoni prevalence or intensity.…”

Socioeconomic determinants of schistosomiasis in a poor rural area in Brazil

“…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, 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 noncausal determinism, which posits that socioeconomic conditions determine and operate through various conditioning factors, or intermediate mechanisms, not necessarily in a causal manner.…”