A multivariate analysis of socio-demographic factors, water contact patterns and Schistosoma mansoni infection in an endemic area in Brazil

FioSchisto's expert perspective on implementing WHO guidelines for schistosomiasis control and transmission elimination in Brazil

The World Health Organization (WHO) recognizes schistosomiasis as one of the Neglected Tropical Diseases targeted for global elimination in the 2030 Agenda of the Sustainable Development Goals. In Brazil, schistosomiasis mansoni is considered a public health problem, particularly prevalent among vulnerable populations living in areas with poor environmental and sanitary conditions. In 2022, the WHO published a Guideline encompassing recommendations to assist national programs in endemic countries in achieving morbidity control, eliminating schistosomiasis as a public health problem, and advancing towards interrupting transmission. The perspectives presented here, collectively prepared by members of the Oswaldo Cruz Foundation's (Fiocruz) Schistosomiasis Translational Program (FioSchisto), along with invited experts, examine the feasibility of the WHO recommendations for the Brazilian settings, providing appropriate recommendations for public health policies applicable to the epidemiological reality of Brazil, and suggests future research to address relevant issues. In Brazil, the provision of safe water and sanitation should be the key action to achieve schistosomiasis elimination goals. The agencies involved in measures implementation should act together with the Primary Care teams for planning, executing, monitoring, and evaluating actions in priority municipalities based on their epidemiological indicators. Host snails control should prioritize judicious ecological interventions at breeding sites. The Information, Education, and Communication (IEC) strategy should be associated with water and sanitation and other control actions, actively involving school community. To identify infected carriers, FioSchisto recommends a two-stage approach of immunological and molecular tests to verify transmission interruption during the intervention and beyond. Praziquantel administration should be done under medical supervision at the Primary Care level. MDA should be considered in exceptional settings, as a measure of initial attack strategy in locations presenting high endemicity, always integrated with water and sanitation, IEC, and snail control. To assist decision-making, as well as the monitoring and evaluation of strategic actions, there is a need for an Information System. FioSchisto considers this systematization essential to make investments in strategic research to support the improvement of schistosomiasis control actions. Efforts toward schistosomiasis elimination in Brazil will succeed with a paradigm shift from the vertical prescriptive framework to a community-centered approach involving intersectoral and interdisciplinary collaboration.

Effect of environmental factors in reducing the prevalence of schistosomiasis in schoolchildren: An analysis of three extensive national prevalence surveys in Brazil (1950-2018)

BACKGROUND

Over seven decades, Brazil has made admirable progress in controlling schistosomiasis, and a frequent question about the explanation for this reduction refers to the effect of improving environmental factors in the country. This article seeks to identify factors related to the change in the epidemiological situation of schistosomiasis mansoni infection by analyzing three national prevalence surveys conducted since 1950.

METHODOLOGY/PRINCIPAL FINDINGS

This is an ecological study analyzing an unbalanced panel of data based on national surveys and considering the municipality as the unit of analysis. The sample consisted of 1,721 Brazilian municipalities, in which a total of 1,182,339 schoolchildren aged 7-14 were examined during the three periods corresponding to each survey (1947-1953, 1975-1979, and 2010-2015). The percentage of municipalities with zero cases of schistosomiasis was: 45.4%, 54.2% and 73.7%, respectively for those periods. A zero-inflated Poisson regression model, with fixed and random effects, was fitted to assess the association between candidate factors and disease prevalence using a significance level of 5%. There was a significant decrease in disease prevalence between the first and last periods analyzed (RR 0.214, CI 0.184-0.249), with a protective association with access to sanitation (RR 0.996, CI 0.994-0.998), urbanization (RR 0.991, CI 0.989-0.993), and living in own households (RR 0.986, CI 0.983-0.989); and an inverse association with piped water supply (RR 1.010, CI 1.008-1.011).

CONCLUSION

The findings of this study indicate a decrease in the prevalence of schistosomiasis over seven decades in schoolchildren from the analyzed Brazilian municipalities, associated with environmental factors and social conditions. The increased access to piped water in the municipalities apparently triggers other ways of contact with unsafe water bodies, generating new transmission routes and suggesting the need for a systemic approach concerning contact with water.

Unprotected water sources and low latrine coverage are contributing factors to persistent hotspots for schistosomiasis in western Kenya

BACKGROUND

Evidence indicates that whereas repeated rounds of mass drug administration (MDA) programs have reduced schistosomiasis prevalence to appreciable levels in some communities referred to here as responding villages (R). However, prevalence has remained high or less than anticipated in other areas referred to here as persistent hotspot villages (PHS). Using a cross-sectional quantitative approach, this study investigated the factors associated with sustained high Schistosoma mansoni prevalence in some villages despite repeated high annual treatment coverage in western Kenya.

METHOD

Water contact sites selected based on observation of points where people consistently go to collect water, wash clothes, bathe, swim or play (young children), wash cars and harvest sand were mapped using hand-held smart phones on the Commcare platform. Quantitative cross-sectional surveys on behavioral characteristics were conducted using interviewer-based semi-structured questionnaires administered to assess water usage/contact patterns and open defecation. Questionnaires were administered to 15 households per village, 50 pupils per school and 1 head teacher per school. One stool and urine sample was collected from 50 school children aged 9-12 year old and 50 adults from both responding (R) and persistent hotspot (PHS) villages. Stool was analyzed by the Kato-Katz method for eggs of S. mansoni and soil-transmitted helminths. Urine samples were tested using the point-of-care circulating cathodic antigen (POC-CCA) test for detection of S. mansoni antigen.

RESULTS

There was higher latrine coverage in R (n = 6) relative to PHS villages (n = 6) with only 33% of schools in the PHS villages meeting the WHO threshold for boy: latrine coverage ratio versus 83.3% in R, while no villages met the girl: latrine ratio requirement. A higher proportion of individuals accessed unprotected water sources for both bathing and drinking (68.5% for children and 89% for adults) in PHS relative to R villages. In addition, frequency of accessing water sources was higher in PHS villages, with swimming being the most frequent activity. As expected based upon selection criteria, both prevalence and intensity of S. mansoni were higher in the PHS relative to R villages (prevalence: 43.7% vs 20.2%; P < 0.001; intensity: 73.8 ± 200.6 vs 22.2 ± 96.0, P < 0.0001), respectively.

CONCLUSION

Unprotected water sources and low latrine coverage are contributing factors to PHS for schistosomiasis in western Kenya. Efforts to increase provision of potable water and improvement in latrine infrastructure is recommended to augment control efforts in the PHS areas.

Multivariate analysis of factors associated with Schistosoma mansoni and hookworm infection among primary school children in rural Bahir Dar, Northwest Ethiopia

BACKGROUND

Soil-transmitted helminths and Schistosoma mansoni infections are the major causes of morbidity and mortality in Sub-Saharan countries. The highest burden of the disease resides in school-age children. Poor water sanitation and hygiene are believed to be the major contributing factors for the high prevalence. Therefore, the goal of this study was to determine the prevalence of intestinal parasite infections in rural Bahir Dar, Northwest Ethiopia.

METHODS

A cross-sectional study was conducted from April 2017-June 2017 among 409 randomly selected primary school children. A structured questionnaire was used to obtain socio-demographic information and determinant factors through interviewing the students. Stool examination was done by Ritchie's concentration method. The data were entered and analyzed using SPSS version 22. Prevalence of helminthic infections was calculated using descriptive statistics. The association between helminthic infection and determinant factors was determined by Bavarian regression. The confounding effect was checked by multivariate regression at 95% confidence interval. Any association was significant when the p-value was < 0.05.

RESULT

The overall prevalence of intestinal parasite infection was 47.2%.(193/409).. The prevalence of Hookworm species and Schistosoma mansoni was 31.1 and 8.0%, respectively. Co-infection of Hookworm species with Schistosoma mansoni was 5.1% (21/409). The highest prevalence of Schistosoma mansoni was recorded for boys (21%), older children (21.4%) and rural children (17.6%) (P < 0.05). Schistosoma mansoni infection was also higher among children whose household drinking water was sourced from streams/rivers (P < 0.05). The multivariate analysis showed lower odds of Schistosoma mansoni infection for those with no history of bathing (AOR = 3.7, 95% CI: 1.1-12.2; P = 0.034), washing clothes/utensils (AOR = 3.4; 95% CI: 1.2-9.7; P = 0.022), swimming (AOR = 2.8, 95% CI: 1.2-6.9; P = 0.023), and irrigation (AOR = 2.8, 95% CI: 1.3-6.0; P = 0.01). Significantly, higher odds of Hookworm infection was recorded for older children (AOR = 2.3, 95% CI: 1.08-4.89; P = 0.029), boys (AOR = 1.9, 95% CI: 1.12-3.24; P = 0.018), and rural children (AOR = 1.8, 95% CI: 1.04-3.0; P = 0.037). Regular shoe wearing (AOR = 0.29, 95% CI: 0.16-0.50; P = 0.00) is protective for hookworm infection. Higher odds of hookworm infection was also recorded for schoolchildren who had the habit of eating raw vegetables (AOR = 1.2 95% CI: 1.1-1.7 P = 0.011).

CONCLUSION

Hookworm infection and schistosomiasis are prevalent in the school children in rural Bahir Dar in Northwest Ethiopia. Various activities and behaviors of the children were strongly associated with helminthic infection. Hence health education should be delivered regularly to minimize/avoid the risky behaviors and water-based activities. Deworming programs should also be implemented on a regular basis.

Repeated praziquantel treatments remodel the genetic and spatial landscape of schistosomiasis risk and transmission

Repeated treatments with praziquantel reduce schistosomiasis prevalence and morbidity, but transmission persists and populations often recover within a few years. To identify factors associated with persistence, we surveyed and treated all identified Schistosoma mansoni infections in two rural Brazilian communities (Jenipapo and Volta do Rio) in 2009, 2012 and 2013. Eggs were collected from all infected individuals and genotyped with 11 microsatellite markers to evaluate parasite differentiation and diversity. After successive rounds of community-wide treatment, prevalence decreased from 45% to 24% then 16%. Intensity of infection decreased by 57% over this period, and the number of eggs transmitted to the environment decreased by 92%. During all time periods the majority of eggs were excreted by those >15years of age. The incidence was 23% in 2012 and 15% in 2013, consistent with a decrease in transmission. There was little immigration or gene flow over a distance of 6km. On reinfection, infrapopulations were moderately differentiated indicating that pretreatment multilocus genotypes were not fully reacquired. The effective population size responded to census population decline more rapidly than differentiation. Reinfection was concentrated in the downstream portion of Jenipapo, consistent with the observed increased human fecal contamination. At this scale and in this area S. mansoni infections exist on a fragmented landscape with a highly focal pattern of transmission that may facilitate future elimination.

The relationship between water, sanitation and schistosomiasis: a systematic review and meta-analysis

Background

Access to “safe” water and “adequate” sanitation are emphasized as important measures for schistosomiasis control. Indeed, the schistosomes' lifecycles suggest that their transmission may be reduced through safe water and adequate sanitation. However, the evidence has not previously been compiled in a systematic review.

Methodology

We carried out a systematic review and meta-analysis of studies reporting schistosome infection rates in people who do or do not have access to safe water and adequate sanitation. PubMed, Web of Science, Embase, and the Cochrane Library were searched from inception to 31 December 2013, without restrictions on year of publication or language. Studies' titles and abstracts were screened by two independent assessors. Papers deemed of interest were read in full and appropriate studies included in the meta-analysis. Publication bias was assessed through the visual inspection of funnel plots and through Egger's test. Heterogeneity of datasets within the meta-analysis was quantified using Higgins' I².

Principal Findings

Safe water supplies were associated with significantly lower odds of schistosomiasis (odds ratio (OR) = 0.53, 95% confidence interval (CI): 0.47–0.61). Adequate sanitation was associated with lower odds of Schistosoma mansoni, (OR = 0.59, 95% CI: 0.47–0.73) and Schistosoma haematobium (OR = 0.69, 95% CI: 0.57–0.84). Included studies were mainly cross-sectional and quality was largely poor.

Conclusions/Significance

Our systematic review and meta-analysis suggests that increasing access to safe water and adequate sanitation are important measures to reduce the odds of schistosome infection. However, most of the studies were observational and quality was poor. Hence, there is a pressing need for adequately powered cluster randomized trials comparing schistosome infection risk with access to safe water and adequate sanitation, more studies which rigorously define water and sanitation, and new research on the relationships between water, sanitation, hygiene, human behavior, and schistosome transmission.

Schistosomiasis is a serious disease in many developing countries, and the control of schistosomiasis relies on the large-scale administration of praziquantel. However, this strategy fails to address the root causes of schistosomiasis, which people acquire during contact with freshwater bodies that contain infected snails. It is suggested that improving access to clean water and sanitation reduces the risk of schistosomiasis transmission. Moreover, the use of soap, detergent, and endod (a berry sometimes used as a substitute for soap) might kill snails and the parasite larvae they excrete. We systematically reviewed the literature and performed a meta-analysis to study the association between people's access to clean water, sanitation, and good hygiene and the risk of schistosomiasis. People with access to clean water and adequate sanitation were at lower risks of schistosomiasis. No studies were found to explore the relationship between hygiene and risk of schistosomiasis. The difference in infection rates between people with and without access to clean water and sanitation varies widely between studies, suggesting that the impact of water and sanitation on schistosomiasis transmission is mediated by many other social and environmental factors. Further research is needed on the impact of water, sanitation and hygiene interventions for schistosomiasis control.

Sex bias in infectious disease epidemiology: patterns and processes

BACKGROUND

Infectious disease incidence is often male-biased. Two main hypotheses have been proposed to explain this observation. The physiological hypothesis (PH) emphasizes differences in sex hormones and genetic architecture, while the behavioral hypothesis (BH) stresses gender-related differences in exposure. Surprisingly, the population-level predictions of these hypotheses are yet to be thoroughly tested in humans.

METHODS AND FINDINGS

For ten major pathogens, we tested PH and BH predictions about incidence and exposure-prevalence patterns. Compulsory-notification records (Brazil, 2006-2009) were used to estimate age-stratified ♂:♀ incidence rate ratios for the general population and across selected sociological contrasts. Exposure-prevalence odds ratios were derived from 82 published surveys. We estimated summary effect-size measures using random-effects models; our analyses encompass ∼0.5 million cases of disease or exposure. We found that, after puberty, disease incidence is male-biased in cutaneous and visceral leishmaniasis, schistosomiasis, pulmonary tuberculosis, leptospirosis, meningococcal meningitis, and hepatitis A. Severe dengue is female-biased, and no clear pattern is evident for typhoid fever. In leprosy, milder tuberculoid forms are female-biased, whereas more severe lepromatous forms are male-biased. For most diseases, male bias emerges also during infancy, when behavior is unbiased but sex steroid levels transiently rise. Behavioral factors likely modulate male-female differences in some diseases (the leishmaniases, tuberculosis, leptospirosis, or schistosomiasis) and age classes; however, average exposure-prevalence is significantly sex-biased only for Schistosoma and Leptospira.

CONCLUSIONS

Our results closely match some key PH predictions and contradict some crucial BH predictions, suggesting that gender-specific behavior plays an overall secondary role in generating sex bias. Physiological differences, including the crosstalk between sex hormones and immune effectors, thus emerge as the main candidate drivers of gender differences in infectious disease susceptibility.

Factors associated with resistance to Schistosoma mansoni infection in an endemic area of Bahia, Brazil

Detailed knowledge of factors associated with resistance to Schistosoma mansoni infection in endemic areas might facilitate more effective schistosomiasis control. We conducted a cross-sectional study of persons resistant to schistosomiasis and found no association between socioeconomic status and resistance to infection. Mononuclear cells of resistant subjects produced higher levels of interleukin-5 (IL-5), IL-13 and interferon-γ upon stimulation with soluble egg antigen (SEA) compared with infected persons. When stimulated with Sm21.6 or Sm22.6, levels of IL-10 were higher in cell culture of resistant persons. Levels of IgE against soluble adult worm antigen (SWAP) and against interleukin-4-inducing principle from S. mansoni eggs (IPSE) and levels of IgG4 against SWAP, SEA, and Sm22.6 were lower in the resistant group compared with the susceptible group. Our data suggest that socioeconomic status could not fully explain resistance to S. mansoni infection observed in the studied area. However, a mixture of Th1 and Th2 immune responses and low levels of specific IgG4 against parasite antigens could be mediating resistance to infection.

Schistosoma mansoni infection in a rural area of the Jequitinhonha Valley, Minas Gerais, Brazil: analysis of exposure risk

This study examines the relative contribution of age-specific total IgE levels, eosinophils and water contact behavior to the prevalence and intensity (geometric mean egg counts) of Schistosoma mansoni infection in the poor rural population of Virgem das Graças in northern Minas Gerais State. In bivariate analysis, age was strongly correlated with both prevalence and intensity of infection, while eosinophil levels with prevalence only (p<0.0001); IgE levels and 5 demographic and socioeconomic variables were moderately correlated with prevalence (p<0.05), as were number of persons per room and TBM (total body minutes) with egg counts. In multivariate analysis, after controlling for demographic and socioeconomic factors, only total IgE levels were significantly correlated with both prevalence (p=0.248, 95% CI=1.01-1.11) and intensity (p=0.0217, 95% CI=0.01-0.14) of infection and eosinophil levels with prevalence (p=0.0005, 95% CI=1.07-1.24). Although any causal relationship cannot be confirmed by a cross-sectional study, we demonstrated an associated decrease in prevalence and intensity of S. mansoni infection with increased IgE levels.

Prevalence distribution and risk factors for Schistosoma hematobium infection among school children in Blantyre, Malawi

BACKGROUND

Schistosomiasis is a public health problem in Malawi but estimates of its prevalence vary widely. There is need for updated information on the extent of disease burden, communities at risk and factors associated with infection at the district and sub-district level to facilitate effective prioritization and monitoring while ensuring ownership and sustainability of prevention and control programs at the local level.

METHODS AND FINDINGS

We conducted a cross-sectional study between May and July 2006 among pupils in Blantyre district from a stratified random sample of 23 primary schools. Information on socio-demographic factors, schistosomiasis symptoms and other risk factors was obtained using questionnaires. Urine samples were examined for Schistosoma hematobium ova using filtration method. Bivariate and multiple logistic regressions with robust estimates were used to assess risk factors for S. hematobium. One thousand one hundred and fifty (1,150) pupils were enrolled with a mean age of 10.5 years and 51.5% of them were boys. One thousand one hundred and thirty-nine (1,139) pupils submitted urine and S. hematobium ova were detected in 10.4% (95%CI 5.43-15.41%). Male gender (OR 1.81; 95% CI 1.06-3.07), child's knowledge of an existing open water source (includes river, dam, springs, lake, etc.) in the area (OR 1.90; 95% CI 1.14-3.46), history of urinary schistosomiasis in the past month (OR 3.65; 95% CI 2.22-6.00), distance of less than 1 km from school to the nearest open water source (OR 5.39; 95% CI 1.67-17.42) and age 8-10 years (OR 4.55; 95% CI 1.53-13.50) compared to those 14 years or older were associated with infection. Using urine microscopy as a gold standard, the sensitivity and specificity of self-reported hematuria was 68.3% and 73.6%, respectively. However, the positive predictive value was low at 23.9% and was associated with age.

CONCLUSION

The study provides an important update on the status of infection in this part of sub-Saharan Africa and exemplifies the success of deliberate national efforts to advance active participation in schistosomiasis prevention and control activities at the sub-national or sub-district levels. In this population, children who attend schools close to open water sources are at an increased risk of infection and self-reported hematuria may still be useful in older children in this region.

Socioeconomic studies of schistosomiasis in Brazil: a review

This review finds considerable evidence that socioeconomic status has significantly influenced the transmission, spread and treatment of schistosomiasis in Brazil. High infection rates persist among both the rural and urban poor. Rural living, poor housing and water supplies and low educational level were major factors in schistosomiasis occurrence among agricultural populations. In urban areas, prevailing living conditions in shantytowns and labor migrations from and periodic return movements to rural areas were predictive of schistosomiasis. The risk of the establishment of new transmission foci exists in both rural and urban areas, conferred by and affecting poorer people. Associations between schistosomiasis and socioeconomic parameters, persisting inequities in health services accessibility, prevailing health impacts of schistosomiasis, and the ongoing decentralization of health services point to opportunities and strategies for focused interventions aimed at promoting health-enhancing behavior and living conditions and improving access to health care. The authors call for multidisciplinary studies to better examine the complexities of the socioeconomic environment in relation to schistosomiasis and for economic programs to reduce prevailing socioeconomic inequalities.

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

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.

Socioeconomic determinants of schistosomiasis in a poor rural area in Brazil

The objective of this paper is to identify and quantify socioeconomic determinants of Schistosoma mansoni infection in the rural area of Virgem das Graças in Minas Gerais State of Brazil. A cross-sectional study was carried out to examine the prevalence and intensity of schistosomiasis in relation to socioeconomic characteristics of the households. Log-binomial regression analysis was used to examine the data on both the household and individual levels, analyzing the prevalence ratios for the association of schistosomiasis and socioeconomic variables related to the head of the household. Multiple comparisons through mixed effect modeling were used to examine the relationship between intensity of infection (geometric mean egg counts) and different levels of socioeconomic variables, respectively. In the univariate analysis, place of residence, number of persons per room, and lack of motorized transport were associated with schistosomiasis at the household level and age and unsafe water contact at the individual level. Age, unsafe water contact, number of persons per room, household possessions and lack of education of head of household remained significant predictors of schistosomiasis in the multivariable analysis. Only age was significantly associated with intensity of infection of individuals. It is concluded that widespread poverty, the rural environment, and weak socioeconomic differentiation that result in intense contact with infective water appear to minimize the protective effect of piped water supply and other socioeconomic parameters on schistosomiasis found in other studies. The potential role of socioeconomic development in conjunction with schistosomiasis control is described and areas for further studies are identified.

The role of nutritional status and insulin-like growth factor in reduced physical growth in hepatosplenic Schistosoma mansoni infection

The influence of nutritional status and hormonal growth activity on the impaired somatic development of adolescents with the hepatosplenic clinical form of Schistosoma mansoni infection (HS), the intestinal form with high (IH) or low (IL) egg output and non-infected (NI) individuals was evaluated (in Comercinho, Minas Gerais State, Brazil, in 1996-97) by measuring body mass index (BMI), insulin-like growth promoting factor (IGF-I) and its carrier protein (IGFBP-3). BMI, IGF-I and IGFBP-3 concentrations were significantly lower in the HS group compared with the IH and the NI groups, irrespective of age. BMI did not remain associated with the clinical form in the bi-variate model that included IGF-I and BMI or IGFBP-3 and BMI, suggesting that in these groups IGF-I and IGFBP-3 levels were related to the clinical form but independent of nutritional status. It is suggested that physical growth impairment in hepatosplenic S. mansoni infection results from the synergistic action of both hepatic damage and nutritional restriction.

The control of schistosomiasis in Brazil: an ethnoepidemiological study of the effectiveness of a community mobilization program for health education

This study combined anthropological and epidemiological approaches to assess the effectiveness of community mobilization for health education, developed as part of the Brazilian program for the control of schistosomiasis. The study was carried out in two villages in the state of Minas Gerais, SE Brazil, exposed to the same established schistosomiaisis control strategies. Residents of one village were also exposed to the community mobilization for health education (study area) while those from the other community were not exposed to this program (control area). Schistosoma mansoni prevalence rates for the study and control villages were compared over time. A population-based survey was carried out in the two villages to obtain information on socio-demographic factors, water contact patterns and knowledge of S. mansoni transmission. Intensive ethnographic interviews with key informants in each locality were employed to determine the knowledge, attitudes and practices of the communities regarding schistosomiasis. Ethnographic data were analysed using the model of systems of signs, meanings and actions. Differences were observed in prevalence trends between the study and control areas but they could not be explained by the existence of the community mobilization program in the former. It was also found that educational actions carried out by the Brazilian Ministry of Health transmitted information on schistosomiasis but were ineffective in transforming the information received into preventive behaviour related to water contact. With regard to disease, the population studied tended to distinguish minor symptoms, which they associated with water contact, from major symptoms, which they attributed to lack of medical treatment. This distinction mediated perceptions of the severity of "xistose" and reduced the importance of avoiding contact with potentially infested waters. The perception of protection conferred by treatment observed in the present study might also apply to other communities where access to treatment is readily available and free. The extent to which this perception exists in endemic areas needs to be determined so that apparent contradictions of this type can be addressed in future educational programs.

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

This paper examines the results of spatial (microgeographical) water contact/schistosomiasis studies in two African (Egyptian and Kenyan) and one Brazilian communities. All three studies used traditional cartographic and statistical methods but one of them employed also GIS (geographical information systems) tools. The advantage of GIS and their potential role in schistosomiasis control are briefly described. The three cases revealed considerable variation in the spatial distribution of water contact, transmission parameters and infection levels at the household and individual levels. All studies showed considerable variation in the prevalence and intensity of infection between households. They also show a variable influence of distance on water contact behavior associated with type of activity, age, sex, socioeconomic level, perception of water quality, season and availability of water in the home. Water contact behavior and schistosomiasis were evaluated in the Brazilian village of Nova União within the context of water sharing between household and age/sex groups. Recommendations are made for further spatial studies on the transmission and control of schistosomiasis.

Schistosomiasis mansoni in the "Baixada Ocidental Maranhense", state of Maranhão, Brazil: cross-sectional studies performed in 1987 and 1993

A cross-sectional study on the prevalence of schistosomiasis mansoni in three sites of the "Baixada Ocidental Maranhense" was carried out in 1993 in: Alegre (in the municipality of São Bento), Aliança (in Cururupu) and Coroatá II (in the municipality of São João Batista). Results were compared to those of another study performed at the same sites and in similar conditions, in 1987. The entire population of the three sites, with few exceptions, was submitted to fecal tests using the Kato-Katz method and immediate intradermal tests for schistosomiasis in both studies. Subjects with positive results in one of these tests were clinically evaluated by a physical examination. In 1993, the total of 827 subjects were submitted to fecal examination and 826 to intradermal test. Schistosoma mansoni eggs were found in the feces of 154 (18.6%) subjects, while 478 (57.9%) subjects presented a positive intradermal test. Stool examination was carried out in 367 subjects in Alegre with a positivity rate of 14.9%; the intradermal test, performed in 366 subjects, was positive in 47.5% of the cases. In Aliança, 277 subjects had their feces examined and were submitted to an intradermal test, with a positivity rate of 34.4% and 70.7%, respectively. Finally in Coroatá II, 183 inhabitants submitted to fecal and intradermal tests had positivity rates of 2.2% and 59.0%, respectively. When the present data were compared to those obtained in the survey performed in 1987, a significant decrease in the prevalence of infection by S. mansoni was observed in Alegre and Coroatá II, and a prevalence increase in Aliança.

[Sociodemographic and behavioral factors related to schistosomiasis in a rural village of the sugar cane belt in Pernambuco State, Brazil]

Failure of intensive chemotherapy to control schistosomiasis in a highly endemic area of Northeast Brazil led to the hypothesis that sociodemographic and/or behavioral variables could be involved in the persistent transmission. A univariate analysis of such variables in relation to infection by Schistosoma mansoni showed that water contact patterns for recreation and personal hygiene are important risk factors in the area. However, sociodemographic variables were not related to infection, probably because the local population lives under evenly precarious socioeconomic and sanitary conditions. We thus recommend that chemotherapy be combined with other measures like snail control, health education, and improved sanitation and water supply.

Questionnaires in the screening for Schistosoma mansoni infection: a study of socio demographic and water contact variables in four communities in Brazil

The use of questionnaires has been recommended for identifying, at a lower cost, individuals at risk for schistosomiasis. In this study, validity of information obtained by questionnaire in the screening for Schistosoma mansoni infection was assessed in four communities in the State of Minas Gerais, Brazil. Explanatory variables were water contact activities, sociodemographic characteristics and previous treatment for schistosomiasis. From 677, 1474, 766 and 3290 individuals eligible for stool examination in the communities, 89 to 97% participated in the study. The estimated probability of individuals to be infected, if they have all characteristics identified as independently associated with S.mansoni infection, varied from 15% in Canabrava, to 42% in Belo Horizonte, 48% in Comercinho and 80% in São José do Acácio. Our results do not support the hypothesis that a same questionnaire on risk factors could be used in screening for S.mansoni infection in different communities.

[The effectiveness of the Program of Communication and Education in Health on the control of S. mansoni infection in some areas of the state of Bahia]

The Program for S. mansoni Control (PCE) has been developed in some areas of the State of Bahia by the Fundação Nacional de Saúde (FNS). In 1989, activities on Information, Education, Communication and Community Mobilization (IEC/MC) were initiated. This study evaluates the epidemiological impact of the IEC/MC, using a quasi-experimental study design strategy, comparing the prevalences of infection for S. mansoni in areas of IEC/MC and estimates of other areas. The data used were routinely collected by the local staff of the FNS. A decrease on the prevalence of S. mansoni infection was found in all study areas, specially in those of IEC/MC activities. Findings indicate that PCE activities are more effective among school-age individuals and male adults, although IEC/MC allows for higher epidemiological impact among women, reflecting the differences among the strategies. These findings point out the need for qualitative evaluation research, as well as cost benefit and cost effectiveness analyses, that are more appropriate for decision making processes.

Epidemiological characteristics of Schistosoma mansoni infection in rural and urban endemic areas of Minas Gerais, Brazil

To compare the epidemiological profile and socioeconomic factors associated to the infection by Schistosoma mansoni in a rural and an urban endemic area a cross-sectional study was performed in Agua Branca de Minas (rural area) and Bela Fama (urban area), both situated in the State of Minas Gerais, Brazil. Two hundred and eighty eight individuals were surveyed in the rural area and 787 in the urban area. Water contact and socioeconomic questionnaires were used to identify risk factors for the infection. The prevalences of 38.8% and 9.7% and the geometric mean of eggs per gram of faeces of 117.8 and 62.3 were found in the rural and urban areas, respectively. By multivariate statistical analysis age groups over nine years old and previous specific treatment were associated with the infection in rural area. In urban area age over nine years old, low quality housing, weekly fishing and swimming were associated after adjustment by logistic regression.

Water-contact patterns and risk factors for Schistosoma mansoni infection in a rural village of northeast Brazil

Schistosomiasis mansoni in the Serrano village, municipality of Cururupu, state of Maranhão, Brazil, is a widely spread disease. The PECE (Program for the Control of Schistosomiasis), undertaken since 1979 has reduced the prevalence of S. mansoni infection and the hepatosplenic form of the disease. Nevertheless piped water is available in 84% of the households, prevalence remains above 20%. In order to identify other risk factors responsible for the persistence of high prevalence levels, a cross-sectional survey was carried out in a systematic sample of 294 people of varying ages. Socioeconomic, environmental and demographic variables, and water contact patterns were investigated. Fecal samples were collected and analyzed by the Kato-Katz technique. Prevalence of S. mansoni infection was 24.1%, higher among males (35.5%) and between 10-19 years of age (36.6%). The risk factors identified in the univariable analysis were water contacts for vegetable extraction (Risk Ratio--RR = 2.92), crossing streams (RR = 2.55), bathing (RR = 2.35), fishing (RR = 2.19), hunting (RR = 2.17), cattle breeding (RR = 2.04), manioc culture (RR = 1.90) and leisure (RR = 1.56). After controlling for confounding variables by proportional hazards model the risks remained higher for males, vegetable extraction, bathing in rivers and water contact in rivers or in periodically inundated parts of riverine woodland (swamplands).

Avaliação do Programa de Controle da Esquistossomose (PCE/PCDEN) em municípios situados na Bacia do Rio São Francisco, Minas Gerais, Brasil

Foi feita uma avaliação do programa de controle da esquistossomose (PCE/PCDEN) na região da Bacia do Rio São Francisco em Minas Gerais. A área em estudo compreende seis municípios, com 130.000 habitantes e 916 localidades em uma área de 10.722km². As atividades tiveram início em quatro municípios entre 1983 e 1985 e em dois outros em 1987. As principais medidas de controle adotadas foram tratamentos sucessivos com oxamniquine e aplicações de niclosamida em coleções hídricas. A prevalência da infecção pelo Schistosoma mansoni nos primeiros quatro municípios, que inicialmente estava entre 18 e 32%, diminuiu abruplamente após a primeira intervenção (1984/85) e permaneceu em níveis inferiores aos iniciais até a última avaliação realizada (1990/94); tendência semelhante foi observada para a proporção de caramujos infectados. Nestes municípios, a proporção de localidades sem a infecção ou com prevalências inferiores a 5% aumentou em detrimento daquelas com níveis mais altos de prevalência. Nos dois outros municípios, com prevalências iniciais inferiores a 5 %, nãoforam observadas mudanças substanciais nos indicadores endêmicos; a relação custo benefício do programa nos últimos municípios deve ser avaliada e as prioridades redirecionadas para erradicar as áreas focais e prevenir a expansão para áreas indenes. Os autores chamam a atenção para as dificuldades a longo prazo de um programa de controle fundamentado em tratamentos sucessivos. Informações sobre os fatores determinantes da infecção pelo S. mansoni em cada localidade, ou em conjunto de localidades semelhantes, permitiriam a elaboração de medidas complementares ao tratamento mais duradouras e menos dependentes da contínua utilização deste.

Clinical-epidemiologic study of schistosomiasis mansoni in Ponte do Pasmado, a village in the municipality of Itinga, state of Minas Gerais, Brazil, 1992

A clinical-epidemiologic study of schistosomiasis mansoni was conducted in the population of Ponte do Pasmado, a village in the municipality of Itinga, state of Minas Gerais, Brazil. Faecal parasitology by the Kato-Katz method and clinical examination were performed in 93.8% and 82.8% of the local population, respectively. A socioeconomic survey was also made and the signs and symptoms presented by the patients were recorded, as well as their contacts with natural waters. The rate of Schistosoma mansoni infection was 50.3%; the peak of infection occurred during the second decade of life; there was a predominance of low egg counts in faeces (85.89% of positive patients eliminated less than 500 eggs per gram of faeces); the splenomegaly rate was 1.23%. When the risk factors for S. mansoni infection were studied, significant risks were detected in activities such as fetching water, washing dishes, bathing, and crossing streams.

Uso do paradigma de risco para a esquistossomose em áreas endêmicas no Brasil

Neste estudo são confrontados os resultados do uso do paradigma de risco na infecção pelo Schistosoma mansoni em áreas endêmicas no Brasil. Foi observada associação da infecção pelo S. mansoni com algumas condições gerais: ausência de água potável intradomiciliar, baixa renda individual, analfabetismo e residência atual ou anterior em área endêmica por mais de cinco anos. Além dessas condições ocorreu associação com alguns hábitos (fatores de risco) exercer atividades agrícolas e domésticas em águas a céu aberto, nadar e pescar. A análise das condições gerais que podem estar determinando os fatores de risco, apontou o fornecimento de água potável intradomiciliar e o acesso ao tratamento como medidas abrangentes que muitas vezes podem ser adotadas, visando à prevenção e/ou controle da morbidade da endemia. É questionada a eficácia do uso do paradigma de risco na indicação de medidas de controle dessa endemia.

Epidemiologia da esquistossomose mansônica em área de baixa endemicidade

Discutem se padrões epidemiológicos da esquistossomos mansônica em áreas brasileiras de baixa endemicidade que possuem prevalência inferior a 10%, menos de 96 ovos por grama de fezes (epg) e onde os infectados são assintomáticos. Apresentam-se dados do município de Pedro de Toledo (Vale do Ribeira, SP) área de baixa endemicidade cujos resultados foram obtidos de amostragem aleatória devida à agregação de Schistosoma mansoni. Sugere-se substituição de métodos parasitológicos por técnicas sorológicas com maiores sensibilidade e especificidade. O principal fator de risco é o lazer. A infecção predomina nos grupos etários de 10-14, 15-19 e 20-24. A intensidade de infecção foi baixa, com 58,5 epg (média geométrica). Há boa correlação (rs = 0,745) entre intensidade de infecção e prevalência. Os mais altos índices de potencial de contaminação ocorreram nas idades de 5 a 20 anos (57,6%). Os casos autóctones mantêm íntimo contato com Biomphalaria tenagophila, com infecção inferior a 2%. Os padrões de prevalência, de incidência e de intensidade de infecção são semelhantes aos de áreas de moderada e alta endemicidade. Questões sócio-culturais merecem estudo para visão global da epidemiologia.

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

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 (< 10m) 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Schistosomiasis mansoni in an area of low transmission. II. Risk factors for infection

Risk factors for Schistosoma mansoni infection were identified using a 1:1 matched case-control design. The work was conducted in the municipality of Pedro de Toledo, São Paulo State, Brazil, an area where the snail host is Biomphalaria tenagophila. Information on water contact patterns, knowledge, attitudes and practices (kap), socioeconomic and sanitary conditions were obtained by mean of questionnaires. The crude odds ratio estimates and the adjusted odds ratio estimates using the logistic regression model are presented. Most of the examined individuals admitted recent water contacts (90.6% of the cases). The most frequent reason for contact was swimming, playing and fishing and the preferential site of contact was the river. According to the logistic regression technique, the main risk factors for infection were: a) water contact through swimming, playing and fishing; b) fording; c) bad hygiene. We concluded that recreational activities are the main reasons for schistosomiasis transmission in Pedro de Toledo and leisure alternatives should be offered to the local population.

Validity of selected clinical signs and symptoms in diagnosis of Schistosoma mansoni infection

Sensitivity, specificity and positive predictive values of selected clinical signs and symptoms in the diagnosis of Schistosoma mansoni infection were evaluated in 403 individuals (69% of inhabitants over 1 year of age) in an endemic area in Brazil (Divino). Highest sensitivity (13%) was found for blood in stools. Specificity over 90% was found for blood in stools, palpable liver with normal consistency and palpable hardened liver at middle clavicular (MCL) or middle sternal lines (MSL). Hardened liver at MSL (83%) or MCL (75%), and blood in stools (78%) presented higher positive predictive values for S. mansoni infection, while palpable liver with normal consistency at MCL (45%) or MSL (48%) presented smaller values. Enlarged liver without specification of its consistency has been traditionally used as an indicator of the infection in areas where malaria or Kala-azar are not endemic. Our results demonstrate that the probability that a person with blood in stools or hardened palpable liver is infected is higher than among those with palpable liver with normal consistency.