The spatial distribution of Schistosoma mansoni infection before and after chemotherapy in the Jequitinhonha Valley in Brazil

Abstract

Schistosomiasis prevalence and egg counts remained low one year after chemotherapy in most households in a hyperendemic rural area in northern Minas Gerais but several distinct spatial patterns could be observed in relation to IgE levels and to a lesser extent to exposure risk (TBM) and type of water supply. An inverse relationship between pre-treatment household prevalence and egg counts on the one hand and post-treatment IgE levels on the other were noted in two of the five communities. Low exposure risk was associated with the low pre-treatment infection rates in the central village but did not contribute to the decline of infection rates after chemotherapy in the study area, as indicated by the significant increase in water contact during the posttreatment period (p < 0.0001). Distance between households and the streams and socioeconomic factors were also unimportant in predicting the spatial distribution of infection. These results are consistent with the production and antiparasitic effect of high levels of IgE in Schistosoma mansoni infection.Key words: schistosomiasis -chemotherapy -spatial clustering -IgE antibodies -exposure risk -nursing -Brazil Geographical Information Systems (GIS) are increasingly being used in epidemiological and ecological studies of schistosomiasis. Most studies, many of them using GIS in combination with remote sensing techniques, have been carried out at the regional level (Bavia et al. 1999, Brooker & Michael 2000a, Malone et al. 2001, Handzel et al. 2003. The World Health Organization (WHO) recently emphasized the need for studies at the community level in areas where schistosomiasis is gradually being controlled. This includes Brazil, where the national program is making inroads into the prevalence, intensity and pathology of schistosomiasis mostly through chemotherapy and safe water supplies, and where further environmental measures as well as health education have been called for (Katz 1998, WHO 2001.Schistosomiasis tends to cluster within communities, at both the neighborhood and household levels, due to the characteristic focality of risk behavior and transmission (Barreto 1991, Kloos et al. 1998, Bethony et al. 2004. At the household level, spatial information on schistosomiasis can provide information on socioeconomic, behavioral, and genetic factors in parasite transmission and treat- ment because of the socioeconomic cohesion and associated exposure risk and health-seeking behavior of families (Berman et al. 1994, Cairncross et al. 1996, Bethony et al. 2002. In addition, intensity of schistosomiasis infection has been found to decline with increasing distance between households and infective water sources (Kloos et al. 1998, McClennon et al. 2004.The effect of chemotherapy on the spatial distribution of schistosomiasis is poorly known. Different treatment strategies have been associated with fairly predictable reductions in pretreatment infection intensities and transmission levels in Kenya (Butterworth et al. 1991, Sturrock et al. 1994. Similarly, in Côte d'Ivoire...

Avaliação dos fatores de risco cardiovasculares em uma população rural brasileira

“…O comércio, a pecuária de corte, o garimpo e o cultivo de mandioca, milho, feijão, arroz e banana são as principais atividades econômicas da população. A população reside em casas construídas com tijolo de barro e telhas sem rede pública de água nem de esgoto 14 .…”

Directives for Schistosomiasis Control in Endemic Areas of Brazil

“…Thus, the MS recommends that data from stool surveys should include the geographic coordinates of the households obtained by a Global Positioning System (GPS) receptor for later insertion on a digitized map and a georeferenced database. As egg-positive households tend to cluster within communities due to focal characteristics of risk factors and transmission, kernel density exploratory analysis has been of help to assess differences in their spatial distribution patterns and to relate them to potential sources of risk in endemic areas of schistosomiasis in Brazil (Gazzinelli et al, 2006;Araújo et al, 2007;Galvão et al, 2010;Cardin et al, 2011) and China . Figure 1 illustrates the use of kernel density estimator for visually identifying risk areas and comparing the magnitude of spatial clustering in individual infection before and up to one year after treatment with either 40mg/kg or 60mg/kg PZQ single dose.…”

Accessibility to and utilisation of schistosomiasis-related health services in a rural area of state of Minas Gerais, Brazil

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