CD4 and CD8 distribution profile in individuals infected by Schistosoma mansoni.

RATIONALE: Patients with chronic Schistosoma mansoni infection show lower anti-soluble egg antigen (SEA) proliferation responses and higher responses to soluble worm antigen preparation (SWAP). OBJECTIVE: To compare the activation status and proliferation response of peripheral blood mononuclear cells (PBMC) of infected (XTO) and egg-negative individuals (NI) living in the same endemic area. METHODS: XTO (n = 51) and NI individuals from the same geographical area (n = 37) and healthy blood donors (n = 22) were evaluated before and after stimulation with SEA and SWAP. The expression of activation markers (CD4(+) HLADR(+), CD8(high+)HLA-DR(+) and CD8(+) CD28(+)) and proliferation assay was assessed by flow cytometry. FINDINGS: PBMC from infected patients showed lower frequency of CD4(+) but no change in CD8(+) T cells when compared with the healthy donor group. The ratio CD4(+)/CD8(+) was 1.3, 0.6 and 0.5 in healthy donors, infected and non-infected individuals, respectively. The HLA-DR(+) expression on CD8(+) was higher in PBMC from infected and non-infected individuals than from healthy donors, but similar in both total lymphocytes and CD4(+) populations. No intergroup proliferation response differences were observed in CD4(+) and CD8(+) PBMC unstimulated and stimulated with SEA and SWAP. The SEA but not SWAP-stimulated cells showed a decrease in the expression of phosphorylated extracellular signal-regulated kinase (ERK1/2). CONCLUSIONS: XTO and NI individuals living in the same area presented a smaller per cent of CD4(+) and a higher per cent of CD8(+) cells. The activation by either CD8(high+)HLA-DR(+) or CD8(high+)HLA-DR(+)/CD8(+) was enhanced and decreased in XTO and NI by CD8(+) CD28(+) and CD8(+) CD28(+)/CD8(+) when compared with healthy donor. ERK phosphorylation was attenuated in XTO and NI individuals when stimulated with SEA but not SWAP.

Effect of chemotherapy with praziquantel on the production of cytokines and morbidity associated with schistosomiasis mansoni.

The objective of the present study was to test the hypothesis that treatment of schistosomiasis mansoni with praziquantel can alter significantly the immune response of patients and generate a reversal of the level of fibrosis. Peripheral blood mononuclear cell (PBMC) samples were collected from, and abdominal ultrasound examinations conducted on, volunteers infected with Schistosoma mansoni and living in an area where the disease is endemic, both prior to and one year after treatment with praziquantel. Subjects were classified into groups according to the level of pathology (i.e., absent, incipient, moderate, or severe fibrosis). PBMCs were stimulated with schistosome soluble egg antigens (SEA), and the levels of production of the cytokines gamma interferon (IFN-gamma), tumor necrosis factor alpha, transforming growth factor beta, and interleukin-4 (IL-4), IL-10, and IL-13 were determined. The chemotherapy was effective in reducing morbidity, particularly for individuals presenting with severe fibrosis. When levels of cytokine production in posttreatment PBMC cultures stimulated by SEA were categorized as low or high, significant differences in the distribution of IL-13 levels between groups presenting with or not presenting with fibrosis were established. Comparison of pre- and posttreatment SEA-induced cytokine levels in individuals who had experienced no change in the grade of fibrosis following chemotherapy revealed that the level of IFN-gamma decreased in subjects with fibrosis whereas that of IL-10 decreased in individuals with and without fibrosis. The data suggest that chemotherapy is effective in reducing the morbidity of the disease and that the level of IL-13 may be a useful indicator of the persistence of fibrosis following treatment.

Genetic diversity and population structuring of Schistosoma mansoni in a Brazilian village.

The digenean trematode Schistosoma mansoni is responsible for chronic schistosomiasis worldwide, and in Brazil alone an estimated 35 million people are at risk. To evaluate epidemiological patterns among human definitive hosts, we assessed genetic diversity and population subdivision of S. mansoni infrapopulations in human hosts from the highly endemic village of Virgem das Graças in the state of Minas Gerais, Brazil. We believe this is the largest such survey to date. Genetic diversity of parasites, measured over eight polymorphic microsatellite loci, was relatively high and standard measures of inbreeding indicated that the population was panmictic. Furthermore, there was no significant isolation-by-distance of parasite infrapopulations, and measures of population subdivision indicated significant but low to moderate levels of population differentiation. We conclude that patients within this village sample from a broad range of schistosome genetic diversity and effectively act as "genetic mixing bowls" for the parasites. These results contrast with those previously observed in the Brazilian village of Melqui ades and thus provide the opportunity for comparisons of environmental and epidemiological differences that are likely to influence host-parasite coevolution and parasite transmission.

Ageing and Toll-like receptor expression by innate immune cells in chronic human schistosomiasis.

There has been no systematic study of the immune response of individuals aged over 60 years living in Schistosomiasis mansoni-endemic areas, although senescence is reportedly associated with susceptibility to infection and progressive decline in immune function. We have shown previously, in two endemic areas in Minas Gerais, Brazil, that the frequency of individuals aged over 60 years with chronic schistosomiasis is no longer negligible. Moreover, several elderly individuals who have always lived in these endemic areas stay protected from infection. An important question for studies of ageing and disease control in developing countries is which differences in the immunological profile of these negatively tested (non-infected) individuals can account for their resistance to either infection or reinfection. We show, in the present study, that non-infected (negative) elderly individuals develop innate immune mechanisms of protection that replace the age-associated decline in T cell function. Non-infected elderly individuals from endemic areas of schistosome infection present an increase in the frequency of the natural killer (NK) CD56(low) subset of NK cells expressing Toll-like receptors (TLR)-1, -2, -3 and -4 as determined by flow cytometry analysis. In addition, the proportion of dendritic cells expressing TLR-1 is elevated as well as the frequency of monocytes expressing TLR-1 and -4. These results suggest that TLR expression by cells of the innate immune system may be related to the negative status of infection in some elderly individuals who are constantly exposed to S. mansoni. Developing mechanisms of protection from infection may represent a biomarker for healthy ageing in this population.

Cytokine production associated with periportal fibrosis during chronic schistosomiasis mansoni in humans.

Volunteers living in an area where schistosomiasis mansoni is endemic were subjected to ultrasound examination and classified into groups according to the levels of fibrosis diagnosed, namely, absence of indications of fibrosis (group 0), incipient fibrosis (group 1), and moderate/severe fibrosis (group 2). Peripheral blood mononuclear cells (PBMC) collected from the volunteers were stimulated with soluble antigens from adult schistosomes or from schistosome eggs, and the production of the cytokines gamma interferon, tumor necrosis factor alpha, transforming growth factor beta (TGF-beta), interleukin-4 (IL-4), IL-10, and IL-13 was determined. Potential associations of the level of fibrosis with age, sex, intensity of infection, and cytokine production were investigated between the three groups. Univariate analysis identified associations of age (>50), gender (male), and absence of eggs/g of feces with moderate/severe fibrosis and an association of intensity of infection (>100 eggs) with incipient fibrosis. When cytokine production in PBMC cultures stimulated by soluble egg antigens was categorized as low or high, significant differences in the distribution of IL-13 levels were established between groups 0 and 2. No significant differences were detected between the groups in the cytokines produced by PBMC cultures stimulated with soluble antigens from adult schistosomes. When all variables were tested in multivariate analyses, only IL-13 was strongly associated with fibrosis (odds ratio = 5.8; 95% confidence interval [CI] = 1.1 to 30.5). While high levels of TGF-beta appeared to be associated with protection against fibrosis, the strength of the association was low.

Additive host genetic factors influence fecal egg excretion rates during Schistosoma mansoni infection in a rural area in Brazil.

This study quantifies the influence of shared household and kinship on egg counts during Schistosoma mansoni infection in a sample from rural Brazil. Detailed genealogic information allowed assignment of 597 individuals to 6 multihousehold pedigrees residing in 145 households. A variance component method was used to partition egg counts into shared household, additive genetic, and individual-specific environmental effects. Host additive genetic effects consistently accounted for a large proportion of the variation in egg counts: 43% in an unadjusted model and 40% in model adjusted for covariates. In a model that examined the confounding of shared household with kinship, additive genetic effects still accounted for 27% of the variation in egg counts and shared household only 12%. The consistently important role for host additive genetic factors on the variation in egg counts points to new ways of modeling and understanding the mechanisms that contribute to trait variation during infection with S. mansoni.

Genetic epidemiology of fecal egg excretion during Schistosoma mansoni infection in an endemic area in Minas Gerais, Brazil.

There is considerable variation in the level of fecal egg excretion during Schistosoma mansoni infections. Within a single endemic area, the distribution of egg counts is typically overdispersed, with the majority of eggs excreted coming from a minority of residents. The purpose of this study was to quantify the influence of genetic factors on patterns of fecal egg excretion in a rural study sample in Brazil. Individual fecal egg excretions, expressed in eggs per gram of feces, were determined by the Kato-Katz method on stool samples collected on three different days. Detailed genealogic information was gathered at the time of sampling, which allowed assignment of 461 individuals to 14 pedigrees containing between 3 and 422 individuals. Using a maximum likelihood variance decomposition approach, we performed quantitative genetic analyses to determine if genetic factors could partially account for the observed pattern of fecal egg excretion. The quantitative genetic analysis indicated that between 21-37% of the variation in S. mansoni egg counts was attributable to additive genetic factors and that shared environment, as assessed by common household, accounted for a further 12-21% of the observed variation. A maximum likelihood heritability (h2) estimate of 0.44 +/- 0.14 (mean +/- SE) was found for the 9,604 second- and higher-degree pairwise relationships in the study sample, which is consistent with the upper limit (37%) of the genetic factor determined in the variance decomposition analysis. These analyses point to the significant influence of additive host genes on the pattern of S. mansoni fecal egg excretion in this endemic area.

The distribution of Biomphalaria spp. in different habitats in relation to physical, biological, water contact and cognitive factors in a rural area in Minas Gerais, Brazil.

A total of 256 sites in 11 habitats were surveyed for Biomphalaria in Melquiades rural area (State of Minas Gerais) in August and November 1999 and in March 2000. Of the 1,780 Biomphalaria collected, 1,721 (96.7%) were B. glabrata and 59 (3.3%) B. straminea. Snails were found in all habitats except in wells, with the largest mean numbers in tanks, seepage ponds and canals, and the smallest numbers in springs, rice fields and fishponds. People's knowledge of the occurrence of Biomphalaria at the collection sites and the presence of Biomphalaria ova were strongly correlated with the occurrence of snails, and distance between houses and collection sites, as well as water velocity were inversely correlated with Biomphalaria occurrence (p < 0.001). The strongest predictor o f Biomphalaria occurrence was the presence of tilapia fish in fishponds. Fourteen Biomphalaria (0.8% of all snails) found at 6 sites were infected with Schistosoma mansoni. Suggestions are made for the utilization of local people's knowledge in snail surveys and further studies are recommended on the possible use of tilapia for biological control of Biomphalaria in fishponds, as well as modeling of S. mansoni transmission and reinfection.

Genetic epidemiology of fecal egg excretion during Schistosoma mansoni infection in an endemic area in Minas Gerais, Brazil

There is considerable variation in the level of fecal egg excretion during Schistosoma mansoni infections. Within a single endemic area, the distribution of egg counts is typically overdispersed, with the majority of eggs excreted coming from a minority of residents. The purpose of this study was to quantify the influence of genetic factors on patterns of fecal egg excretion in a rural study sample in Brazil. Individual fecal egg excretions, expressed in eggs per gram of feces, were determined by the Kato-Katz method on stool samples collected on three different days. Detailed genealogic information was gathered at the time of sampling, which allowed assignment of 461 individuals to 14 pedigrees containing between 3 and 422 individuals. Using a maximum likelihood variance decomposition approach, we performed quantitative genetic analyses to determine if genetic factors could partially account for the observed pattern of fecal egg excretion. The quantitative genetic analysis indicated that between 21-37 percent of the variation in S. mansoni egg counts was attributable to additive genetic factors and that shared environment, as assessed by common household, accounted for a further 12-21 percent of the observed variation. A maximum likelihood heritability (h²) estimate of 0.44 ± 0.14 (mean ± SE) was found for the 9,604 second- and higher-degree pairwise relationships in the study sample, which is consistent with the upper limit (37 percent) of the genetic factor determined in the variance decomposition analysis. These analyses point to the significant influence of additive host genes on the pattern of S. mansoni fecal egg excretion in this endemic area

Exposure to Schistosoma mansoni infection in a rural area of Brazil. I: water contact.

The study of water contact patterns in rural Brazil presents unique challenges due to widely dispersed settlement patterns, the ubiquity of water contact sites, and the privatization of water resources. This study addresses these challenges by comparing the two most widely used methods of assessing water contact behaviour: direct observation and survey. The results of a 7-day direct observation of water contact were compared with water contact surveys administered 1 week after and then 1 year after the direct observation study. The direct observation study recorded a water contact rate higher than reported by other investigators (3.2 contacts per person per day); however, 75% of these contacts were for females and consisted mainly of domestic activities occurring around the household. A comparison of the frequency of water contact activities between the direct observation and the two surveys revealed several important points. First, no significant differences were found between methods for routine water contact activities (e.g. bathing), indicating that participants were able to accurately self-report some types of water contact activities. Second, significant differences were found in the recording of water contact activities that took place outside the observation area, indicating that direct observation may under-report water contact activities in areas where contact sites are dispersed widely. Third, significant differences between the direct observation and the survey method were more common for males than for females, indicating that the combination of widespread water contact sites and gender-specific division of labour may result in under-reporting of male contacts by direct observation methods. In short, despite the limitations in the recording of duration and body exposure, the survey method may more accurately record the frequency of water contact activities than direct observation methods in areas of widely dispersed water contact sites. Hence, surveys may be more suitable for the unique challenges of water contact in rural areas of Brazil.

Exposure to Schistosoma mansoni infection in a rural area in Brazil. II: household risk factors.

A number of studies have pointed out the potential importance of the household in the transmission of schistosomiasis. The clustering of domestic activities associated with water collection, storage, and usage can result in the sharing of transmission sites and infective water contact behaviours. In this study, we employed a variance component method to estimate effects due to individual risk factors and shared residence on the variance in faecal egg counts during Schistosoma mansoni infection. A suite of covariates, which included demographic, socioeconomic, water supply, and water contact behaviour terms, contributed 15% to the variance in faecal egg counts. Shared residence alone accounted for 28% of the variance in faecal egg excretion. When both the suite of covariates and shared residence were considered in the same model, shared residence still contributed 22% to the variance in infection intensity. These results point to the importance of shared residence as a means of capturing the complex interrelationship between shared demographic, socioeconomic, physical environmental, and behavioural factors that influence transmission of schistosomiasis at the household level.

Domestic water use in a rural village in minas gerais, brazil, with an enphasis on spatial patterns, sharing of water, and factors in water use

This paper examines the relationship between domestic water use and socioeconomic, environmental, and spatial parameters at the household level in a small rural village in northern Minas Gerais State. Five methods are used - direct observation, household interviews, self-reporting by households, regression analysis, and statistical mapping. Results show that water use is characterized by 1) generally low but widely fluctuating values per person per day, 2) sharing of water sources between households, 3) the use of multiple sources by individual households, 4) avoidance of heavily contaminated stream sites, and 5) predominance of socioeconomic factors in water use. Households owning their own water supply used, on average, 25.3 liters per person/day and those without a supply 9. 0 l, with higher use of the local streams among the latter. Water use varied spatially. The socioeconomic factors house quality, latrine ownership, type of watersource, and a utility index were significantly correlated with water use. Implications of this simple household water sources and the more deficient sanitary facilities for potential water-borne disease transmission are briefly discussed and suggestions made for further improvements. This study confirms the appropriateness of the application of direct observation, interview, and microgeographical methods for quantitative water use studies.

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.

Sociocultural aspects of schistosomiasis mansoni in an endemic area in Minas Gerais, Brazil.

A study to determine the sociocultural factors influencing knowledge, attitudes, and practices of individuals from a small community toward Schistosoma mansoni infection was carried out in an endemic area in the State of Minas Gerais, Brazil. The study used qualitative approaches to collect data from school-aged children and teachers. Specific findings were that the individuals interviewed were aware of the disease, but also held inaccurate popular beliefs about transmission. Misconceptions coexisted with accurate knowledge both in children and teachers. The disease was not seen as a major health problem and does not affect their activities since it does not cause severe symptoms in most of the individuals. Although the majority of the participants relate transmission to water and lack of sanitation, they do not take any preventive measures since their subsistence is highly dependent on irrigation, farming, fishing, and other essential work that is directly related to water activities. The authors discuss the development of a health education program based on the knowledge and perception of individuals about the disease and its determinants as being important for the context and behavioral change.