The effects of ingesting plant hormones on schistosomiasis in mice: An experimental study

A number of studies have shown that primates monitor and select plant species in their diet as a function of their secondary compound composition. The possibility also exists that secondary compounds, when used in appropriate concentrations, may have a beneficial, medicinal aspect. In this regard, synthesis of a variety of data suggested a connection between selection of Balanites by Ethiopian baboons, and the distribution of schistosomiasis. To test the hypothesis that the secondary compounds in Balanites might be selected for ‘medicinal purposes’, we conducted an experiment on the effect of adding the active principle, diosgenin, to the food of schistosome-infected mice. The hypothesis was that this steroidal saponin might alter the host's hormonal milieu, making a less hospitable environment for the adult schistosomes. Sacrifice of the mice showed diosgenin-fed animals to have an augmented rather than decreased response to the disease. However, the data support the developing literature that shows that the host's hormonal environment has a major effect on the parasitic diseases they are subject to, and that the hormonal environment can be dramatically influenced by the secondary compounds in the diet.     

Schistosomiasis in Lake Malawi: Relationship of Fish and Intermediate Host Density to Prevalence of Human Infection

Prior to 1985, the open waters of Lake Malawi were free from schistosome transmission. Over the past decades, however, the prevalence of urinary schistosomiasis has increased dramatically in the southern part of the lake. We found the prevalence of human schistosomiasis in school-aged children to be negatively correlated with the density of molluscivorous fishes. Specifically, the increased infection rate in southern Lake Malawi between 1978 and 1991 is coincident with the reduction in numbers of snail-eating fishes. During 2003, we determined the relative abundance of molluscivorous fishes and snail density at 18 sites throughout the lake and schistosome infection in school-aged children living in selected lakeshore communities of Lake Malawi. At the 18 sites sampled in 2003, we found that snail abundance decreased with an increase in abundance of snail-eating fishes. Furthermore, the 2003 samples showed that the abundance of snail-eating fishes increased and there was a reduction in schistosomiasis in school-aged children in Chembe Village. We believe that we will not observe a return to the 1978 infection rates until these fishes continue to increase and inhabit shallower waters.     

The socio-economic effects of tropical diseases in Nigeria

Urinary schistosomiasis is the most prevalent of the endemic tropical diseases: 48% of the population is afflicted in the study area. The socio-economic, environmental and health-seeking behavioural characteristics of the population are conducive to the spread of urinary schistosomiasis. The attitudes considered include knowledge of what causes the disease and how to control it, attitude toward the disease, care of oneself, hygiene and sanitation. The effect of such social variables as stigmatisation, and environmental variables such as water source is also considered. We find that a unit increase in the hygiene/sanitation index for adult males and adult females lead to a reduction of about 7.3 and 4.0 eggs S. haematobium in 10 ml urine sample, respectively. Thus, simple hygienic activities such as keeping the immediate environment of the household free from human wastes contribute substantially to disease control. Furthermore, prevalence of the disease is higher among males. Losses from work attributed to urinary schistosomiasis are high. Average values of key socio-economic variables-labour flow for land clearing, farm size and cash income-computed for farm families with high urinary schistosomiasis intensity in the sample are 1085 h, 1.4 ha and N 1,432 (US dollars 65) respectively. The corresponding figures for farm families free from the disease are significantly higher: 1325 h, 1.9 ha and N 3,759 (US dollars 171), respectively.     

The effect of calcium concentration on the crushing resistance, weight and size of Biomphalaria sudanica (Gastropoda: Planorbidae)

Biomphalaria sudanica (intermediate host of Schistosoma mansoni) were raised in the laboratory in media with seven different calcium concentrations ranging from 0.02 to 2.0 mmol/l. After 10 weeks, snails were killed and shell diameter, inorganic dry weight, ash free dry weight and crushing resistance were measured. Snails raised at lower calcium concentrations were found to be significantly smaller than snails raised at higher concentrations. Furthermore, relatively thinner shells were developed at low concentrations and crushing resistance relative to snail size was found to be lower for these snails. The ratio between crushing resistance and ash free dry weight (as a measure for the energetic cost/benefit-ratio) was also found to be correlated with calcium concentration. The relevance of the results for predation risk of B. sudanica is discussed.     

脑血吸虫与脑肺吸虫病的MRI诊断与鉴别诊断

目的：探讨总结脑血吸虫病与脑肺吸虫病MRI影像特点,更好的指导临床旱期诊断。方法：回顾分析10例脑血吸虫及9例脑肺吸虫的MRI影像特点,总结分析其影像征象及价值。结果：脑血吸虫和肺吸虫病临床表现类似,均以颅内压增高和癫痫为主要变现。MRI扫描脑血吸虫病呈多发结节信号,周围大片水肿,增强均匀或不均匀强化;肺吸虫呈斑片样及囊样信号,周围大片水肿,增强扫描环状及斑絮样强化。结论：脑血吸虫与脑肺吸虫病临床表现类似,但MRI有特定的影像特点,可以用来进行诊断。     

Spatial and temporal population genetic survey of Bulinus globosus from Zanzibar: an intermediate host of Schistosoma haematobium

In Zanzibar, the freshwater hermaphroditic snail Bulinus globosus is the intermediate host of the human parasite Schistosoma haematobium . To shed light on the patterns of genetic variation within Bu. globosus , variation at six polymorphic microsatellite loci was assessed to quantify spatial genetic structure within eight populations and temporal changes in a further four populations of the snails. Limited genetic variation was observed within populations, possibly reflecting both partial-selfing and fluctuations in population size. Although a statistically significant heterozygote deficiency was observed, Bu. globosus appears to be a preferential out-crosser, which was consistent with the absence of genotypic linkage disequilibria. Genetic variation across populations was substantial, illustrating significant isolation-by-distance on a regional scale and that gene flow was restricted to nearby populations. The temporal survey showed that levels of genetic variation and inbreeding changed over a 1-year period, consistent with field observations of seasonal change. The results strongly support a snail demographic model of population expansion and contraction throughout the year with habitats re-colonized by aestivating or surviving snails from local refugia. This model might help explain co-evolution of snails and schistosomes in Zanzibar as local populations of Bu. globosus have varying degrees of susceptibility to S. haematobium .     

The role of snail aestivation in transmission of schistosomiasis in changing climatic conditions

Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high.     

Structural and functional characterization of Schistosoma mansoni Thioredoxin

Schistosomiasis, the human parasitosis caused by various species of the blood-fluke Schistosoma, is a debilitating disease affecting 200 million people in tropical areas. The massive administration of the only effective drug, praziquantel, leads to the appearance of less sensitive parasite strains, thus, making urgent the search for new therapeutic approaches and new suitable targets. The thiol-mediated detoxification pathway has been identified as a promising target, being essential during all the parasite developmental stages and sufficiently different from the host counterpart. As a part of a project aimed at the structural characterization of all the proteins involved in this pathway, we describe hereby the high-resolution crystal structure of Schistosoma mansoni Thioredoxin (SmTrx) in three states, namely: the wild-type oxidized adult enzyme and the oxidized and reduced forms of a juvenile isoform, carrying an N-terminal extension. SmTrx shows a typical thioredoxin fold, highly similar to the other components of the superfamily. Although probably unlikely to be a reasonable drug target given its high similarity with the human counterpart, SmTrx completes the characterization of the whole set of thiol-mediated detoxification pathway components. Moreover, it can reduce oxidized glutathione and is one of the few defence proteins expressed in mature eggs and in the hatch fluid, thus confirming an important role in the parasite. We believe its crystal structure may provide clues for the formation of granulomas and the pathogenesis of the chronic disease.     

The dendritic cell-specific C-type lectin DC-SIGN is a receptor for Schistosoma mansoni egg antigens and recognizes the glycan antigen Lewis x

Schistosoma mansoni soluble egg antigens (SEAs) are crucially involved in modulating the host immune response to infection by S. mansoni. We report that human dendritic cells bind SEAs through the C-type lectin dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN). Monoclonal antibodies against the carbohydrate antigens Lewisx (Lex) and GalNAcbeta1-4(Fucalpha1-3)GlcNAc (LDNF) inhibit binding of DC-SIGN to SEAs, suggesting that these glycan antigens may be critically involved in binding. In a solid-phase adhesion assay, DC-SIGN-Fc binds polyvalent neoglycoconjugates that contain the Lex antigen, whereas no binding was observed to Galbeta1-4GlcNAc, and binding to neoglycoconjugates containing only alpha-fucose or oligosaccharides with a terminal alpha1-2-linked fucose is low. These data indicate that binding of DC-SIGN to Lex antigen is fucose-dependent and that adjacent monosaccharides and/or the anomeric linkage of the fucose are important for binding activity. Previous studies have shown that DC-SIGN binds HIV gp120 that contains high-mannose-type N-glycans. Site-directed mutagenesis within the carbohydrate recognition domain (CRD) of DC-SIGN demonstrates that amino acids E324 and E347 are involved in binding to HIV gp120, Lex, and SEAs. By contrast, mutation of amino acid Val351 abrogates binding to SEAs and Lex but not HIV gp120. These data suggest that DC-SIGN recognizes these ligands through different (but overlapping) regions within its CRD. Our data imply that DC-SIGN not only is a pathogen receptor for HIV gp120 but may also function in pathogen recognition by interaction with the carbohydrate antigens Lex and possibly LDNF, which are found on important human pathogens, such as schistosomes and the bacterium Helicobacter pylori.