Widespread heteroplasmy in schistosomes makes an mtVNTR marker "nearsighted"

Mitochondrial markers are often hailed as the preferred DNA elements for analyses of population subdivision. To this end we have employed a mitochondrial repeat element to examine the population structure in Schistosoma mansoni (human blood flukes). Schistosome isolates were collected from each of 21 different patients representing seven different areas of a Brazilian village. These parasite isolates demonstrate substantial genetic polymorphism, with an average of 10 genotypes infecting each patient, which is more readily detected because of high levels of heteroplasmy (i.e., 72.5% of the individual worms exhibit multiple versions of this repeat region with different numbers of repeats). Due to the high number of common haplotypes in the population, this repeat element from S. mansoni has a large proportion (47%) of its genetic variation described by differences among mitochondrial genomes within individual worms. However, when only rare haplotypes are considered, population structure can be detected. It seems that heteroplasmy in the schistosome population of Melquiades is both the source of plentiful genetic variation and a confounding factor in the analysis of that variation. Thus the schistosome population in Melquiades may actually be more strongly subdivided than we are able to detect using this mitochondrial marker.

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.

Cytokines as determinants of resistance and pathology in human Schistosoma mansoni infection

The role of different cytokines in the peripheral blood mononuclear cell (PBMC) proliferative response and in in vitro granuloma formation was evaluated in a cross-sectional study with patients with the different clinical forms and phases of Schistosoma mansoni infection, as well as a group of individuals "naturally" resistant to infection named normal endemic (NE). The blockage of IL-4 and IL-5 using anti-IL-4 and anti-IL-5 antibodies significantly reduced the PBMC proliferative response to soluble egg (SEA) and adult worm (SWAP) antigens in acute (ACT), chronic intestinal (INT) and hepatosplenic (HS) patients. Similar results were obtained in the in vitro granuloma formation. Blockage of IL-10 had no significant effect on either assay using PBMC from ACT or HS. In contrast, the addition of anti-IL-10 antibodies to PBMC cultures from INT patients significantly increased the proliferative response to SEA and SWAP as well as the in vitro granuloma formation. Interestingly, association of anti-IL-4 and anti-IL-10 antibodies did not increase the PBMC proliferative response of these patients, suggesting that IL-10 may act by modulating IL-4 and IL-5 secretion. Addition of recombinant IL-10 decreased the proliferative response to undetectable levels when PBMC from patients with the different clinical forms were used. Analysis of IFN-gamma in the supernatants showed that PBMC from INT patients secreted low levels of IFN-gamma upon antigenic stimulation. In contrast, PBMC from NE secreted high levels of IFN-gamma. These data suggest that IL-10 is an important cytokine in regulating the immune response and possibly controlling morbidity in human schistosomiasis mansoni, and that the production of IFN-gamma may be associated with resistance to infection.

Factors affecting high and low human IgE responses to schistosome worm antigens in an area of Brazil endemic for Schistosoma mansoni and hookworm

We have previously examined the antibody isotype responses to schistosome worm and egg antigens in human populations living in areas of Kenya and the Philippines endemic for Schistosoma mansoni and S. japonicum, respectively. Here, we have analyzed antibody isotype responses to S. mansoni adult worm (AW) antigen and soluble egg antigen (SEA) in more than 500 Brazilian individuals, and found similar relationships with age and sex as in the Kenyan and Filipino populations. Isotype responses to AW antigen broadly increased with age whereas isotype responses to SEA decreased, and a higher proportion of males than females had detectable IgE against AW antigen. Most isotype responses to AW antigen and SEA correlated positively with intensity of infection with S. mansoni except AW antigen-specific IgG2, which correlated negatively. The overall prevalence of infection with S. mansoni in this area was relatively low at only 39.5%; hookworm prevalence was higher at 57.4%. The majority of those infected with S. mansoni were also infected with hookworm (76%). Those individuals with high IgE responses to AW antigen were matched for sex, age, and total IgG to AW antigen as closely as possible with individuals with low levels of AW antigen-specific IgE. The two groups were compared for factors potentially influential in IgE production. No difference was found between the high and low IgE responders for 1) intensity or prevalence of infection with S. mansoni, 2) relative exposure to S. mansoni, 3) number of previous treatments for schistosomiasis, or 4) prevalence of infection with hookworm, but differences were found in other isotype responses to S. mansoni. The high IgE responders had higher IgA and IgG4 against both AW antigen and SEA but lower IgG3 responses to AW antigen than the low IgE responders. The IgE responses to three S. mansoni antigens (paramyosin, Sm22.6, and a 12-kD AW antigen band) were detected in individuals with IgE against AW antigen only.

Immunological profiles of patients from endemic areas infected with Schistosoma mansoni

Crude extracts of eggs (SEA) adult worms (SWAP) or cercariae (Cerc) have been used to stimulate Peripheral Blood Mononuclear cells (PBMC) and have provided rather distinct profiles of responses in different types of patients. In general it is clear that patients with early infections respond strongly to SEA while response to SWAP are develop more slowly. As infection progresses into the more chronic phases, a general pattern is seen which leads to lower anti-SEA proliferative responses in the face of higher responses to SWAP and variable anti-cerc responsiveness. Cured not re-exposed patients express very high levels of anti-SEA proliferation. It has recently been seen that those individuals who live in endemic areas and have continued water contact, but are repeatedly stool-negative (who are presumed to have self-cured or be putatively resistant; endemic normals) are strongly responsive to antigenic extracts, particularly to SEA. Furthermore, our results show that endemic normal individuals have significantly higher IFN gamma production upon PBMC stimulation with schistosome antigens than infected individuals. With the emergence of more studies it is becoming apparent that both the intensity and the prevalence of a given area may influence or shape the general responsiveness of the population under study.