Nutrition and acute schistosomiasis

In northeast Brazil, nutritional deficiency diseases and schistosomiasis mansoni overlap. An experimental model, wich reproduces the marasmatic clinical form of protein-energy malnutrition, was developed in this laboratory to study these interactions. Albino Swiss mice were fed with a food association ingested usually by human populations in northeast Brazil. This diet (Regional Basic Diet - RBD) has negative effects on the growth, food intake and protein utilization in infected mice (acute phase of murine schistosomiasis). Nitrogen balance studies have also shown that infection with Schistosoma mansoni has apparently no effect on protein intestinal absorption in well nourished mice. However, the lowest absorption ratios have been detected among RBD - fed infected animals, suggesting that suprerimposed schistosome infection aggravated the nutritional status of the undernourished host. The serum proteins electrophoretic pattern, as far as albumins are concerned, is quite similar for non-infected undernourished and infected well-fed animals. So, the significance of albumins as a biochemical indicator of the nutritional status of human populations residing in endemic foci of Manson's schistosomiasis, is discussable.

Cercarial Chaetotaxy and Sex Differentiation of Schistosoma mansoni Deriving from Humans and Nectomys squamipes (Muridae: Sigmondontinae) in Brazil

A comparative study was made between sympatric isolates of Schistosoma mansoni: one from a wild rodent (R) Nectomys squamipes and another one from humans (H) isolated from a low endemic schistosomiasis transmission area in Brazil. Our purpose was to detect differences between them concerning chaetotaxy (number and pattern of distribution of the argentophilic papillae) of the cercariae by means of silver impregnation. No significant difference (x > 0.05) between isolates was noted. Nevertheless, a significant difference (x < 0.05) was observed in the cercarial index (ratio of the distance between the first and the second preacetabular papillae and the distance between the first and the second dorsal preacetabular papillae) of male and female cercariae in both isolates. Males presented a greater cercarial index than females. By means of multivariate analysis, male cercariae were distinguished from female cercariae through the following characteristics: average number of dorsal papillae on the right quadrant, average number of ventral middle papillae on the right quadrant (H isolate) and average number of dorsal middle papillae on the left quadrant (R isolate). The results suggest that R and H isolates belong to the same population that could complete its life cycle in rodent-snail-rodent fashion.

Clustering of Schistosoma mansoni mRNA sequences and analysis of the most transcribed genes: implications in metabolism and biology of different developmental stages

The study of the Schistosoma mansoni genome, one of the etiologic agents of human schistosomiasis, is essential for a better understanding of the biology and development of this parasite. In order to get an overview of all S. mansoni catalogued gene sequences, we performed a clustering analysis of the parasite mRNA sequences available in public databases. This was made using softwares PHRAP and CAP3. The consensus sequences, generated after the alignment of cluster constituent sequences, allowed the identification by database homology searches of the most expressed genes in the worm. We analyzed these genes and looked for a correlation between their high expression and parasite metabolism and biology. We observed that the majority of these genes is related to the maintenance of basic cell functions, encoding genes whose products are related to the cytoskeleton, intracellular transport and energy metabolism. Evidences are presented here that genes for aerobic energy metabolism are expressed in all the developmental stages analyzed. Some of the most expressed genes could not be identified by homology searches and may have some specific functions in the parasite.

Intestinal fibrovascular nodules caused by Schistosoma mansoni infection in Calomys callosus Rengger, 1830 (Rodentia: Cricetidae): a model of concomitant fibrosis and angiogenesis

Human schistosomiasis develops extensive and dense fibrosis in portal space, together with congested new blood vessels. This study demonstrates that Calomys callosus infected with Schistosoma mansoni also develops fibrovascular lesions, which are found in intestinal subserosa. Animals were percutaneously infected with 70 cercariae and necropsied at 42, 45, 55, 80, 90 and 160 days after infection. Intestinal sections were stained for brightfield, polarization microscopy, confocal laser scanning, transmission and scanning electron microscopies. Immunohistological analysis was also performed and some nodules were aseptically collected for cell culture. Numerous intestinal nodules, appearing from 55 up to 160 days after infection, were localized at the interface between external muscular layer and intestinal serosa, consisting of fibrovascular tissue forming a shell about central granuloma(s). Intranodular new vessels were derived from the vasculature of the external vascular layer and were positive for laminin, chondroitin-sulfate, smooth muscle alpha-actin and FVIII-RA. Fibroblastic cells and extracellular matrix components (collagens I, III and VI, fibronectin and tenascin) comprised the stroma. Intermixed with the fibroblasts and vessels there were variable number of eosinophils, macrophages and haemorrhagic foci. In conclusion, the nodules constitute an excellent and accessible model to study fibrogenesis and angiogenesis, dependent on S. mansoni eggs. The fibrogenic activity is fibroblastic and not myofibroblastic-dependent. The angiogenesis is so prominent that causes haemorrhagic ascites.

Biomphalaria tenagophila/Schistosoma mansoni interaction: premises for a new approach to biological control of schistosomiasis

Biomphalaria tenagophila is very important for schistosomiasis transmission in Brazil. However its mechanisms of interaction with Schistosoma mansoni are still scantly studied. Since this snail displays strains highly susceptible or completely resistant to the parasite infection, the knowledge of that would be a useful tool to understand the mechanism of snail resistance. Particularly, the Taim strain consistently shows absolute resistance against the trematode, and this resistance is a dominant character. A multidisciplinary research group was created aiming at studying B. tenagophila/S. mansoni interaction. The possibility for applying the knowledge acquired to obtain a biological model for the control of S. mansoni transmission in endemic areas is discussed.

Primary culture of the region of the amebocyte-producing organ of the snail Biomphalaria glabrata, the intermediate host of Schistosoma mansoni

Biomphalaria glabrata snails are major hosts for the digenetic trematoda Schistosoma mansoni, the causative agent of human schistosomiasis. The success or failure of the infection will be dependent on the mobilization of the molluskan internal defense system, where a major role will be played by circulating hemocytes produced by the APO (amebocyte-producing organ) of the snail. In this report, the primary culture of the APO region of B. glabrata was obtained for the first time, as well as a control culture of the ovotestis. Three different cell populations migrated easily from the explants in culture, with no need of any dispersion agent. The cells grew in suspension at an incubation temperature of 15ºC and the cultures were maintained viable for up to two weeks. Two of these cell populations obtained resembled cell types known to be present in the hemolymph of Biomphalaria. The availability of APO cells in culture may contribute to a better understanding of the internal defense in mollusks, in general, as well as the specific response of B. glabrata to S. mansoni infection.

Schistosomiasis risk mapping in the state of Minas Gerais, Brazil, using a decision tree approach, remote sensing data and sociological indicators

Schistosomiasis mansoni is not just a physical disease, but is related to social and behavioural factors as well. Snails of the Biomphalaria genus are an intermediate host for Schistosoma mansoni and infect humans through water. The objective of this study is to classify the risk of schistosomiasis in the state of Minas Gerais (MG). We focus on socioeconomic and demographic features, basic sanitation features, the presence of accumulated water bodies, dense vegetation in the summer and winter seasons and related terrain characteristics. We draw on the decision tree approach to infection risk modelling and mapping. The model robustness was properly verified. The main variables that were selected by the procedure included the terrain's water accumulation capacity, temperature extremes and the Human Development Index. In addition, the model was used to generate two maps, one that included risk classification for the entire of MG and another that included classification errors. The resulting map was 62.9% accurate.

Evolutionary histories of expanded peptidase families in Schistosoma mansoni

Schistosoma mansoni is one of the three main causative agents of human schistosomiasis, a major health problem with a vast socio-economic impact. Recent advances in the proteomic analysis of schistosomes have revealed that peptidases are the main virulence factors involved in the pathogenesis of this disease. In this context, evolutionary studies can be applied to identify peptidase families that have been expanded in genomes over time in response to different selection pressures. Using a phylogenomic approach, we searched for expanded endopeptidase families in the S. mansoni predicted proteome with the aim of contributing to the knowledge of such enzymes as potential therapeutic targets. We found three endopeptidase families that comprise leishmanolysins (metallopeptidase M8 family), cercarial elastases (serine peptidase S1 family) and cathepsin D proteins (aspartic peptidase A1 family). Our results suggest that the Schistosoma members of these families originated from successive gene duplication events in the parasite lineage after its diversification from other metazoans. Overall, critical residues are conserved among the duplicated genes/proteins. Furthermore, each protein family displays a distinct evolutionary history. Altogether, this work provides an evolutionary view of three S. mansoni peptidase families, which allows for a deeper understanding of the genomic complexity and lineage-specific adaptations potentially related to the parasitic lifestyle.

Evolution of schistosomiasis in an hyperendemic area of the Minas Gerais state: two cross-sectional studies

Two cross-sectional studies on schistosomiasis mansoni were done in Comercinho, Minas Gerais (Brazil), at an interval of 7 years. In 1974 and 1981 feces examinations (KATO-KATZ method) were done in 89 and 90% of the population (about 1,500 inhabitants) and clinical examinations were done in 78 and 92% of the patients who excreted Schistosoma mansoni eggs in the feces, respectively. The rate of infection by S. mansoni did not change (69.9% in 1974 and 70.4% in 1981), but the geometrical mean of eggs per gram of feces (431 ± 4 and 334 ± 4, respectively) and the rate of splenomegaly (11 and 7%, respectively) decreased significantly in 1981, when compared to 1974. This reduction was observed only in the central zones of the town (zones 1-2) where the rate of dwellings with piped water increased from 17 to 44%. In the surroundings (zones 3-4), where the proportion of houses with piped water did not change significantly between 1974 (10%) and 1981 (7%), the geometrical mean of S. mansoni eggs and the rate of splenomegaly did not change either.

Serological studies on shistosomiasis mansoni in the Northeast Brasil

Sera from the patients (N = 10) with schistosomiasis mansoni of the hospital of Federal University of Pernambuco, the Schistosoma mansoni egg-positive (N = 51) and -negative (N = 452) inhabitants in Cabo City area, out-patients (N = 37) of the IMIP hospital and Japanese immigrants (N = 127) in Petrolina City area of northeast Brazil as well as Japanese healthy subjects (N = 30) were examined by serological tests including an enzyme-linked immunosorbent assay with antigens prepared from eggs (ELISA-egg) and adult worms (ELISA-adult). The ELISA with egg or adult antigen correctly identified 100% of the uninfected individuals lived in non-endemic area of schistosomiasis. Moreover, when examined cross-reactivity of our ELISA with sera isolated from 78 subjects infected with various intestinal parasitic infections, only one of these sera reacted with the egg and adult antigens. On the examination of 51 sera from the egg-positive subjects, the ELISA-egg revealed the highest sensitivity (98.0%), whereas a large number of false negative reactions of ELISA-adult, Ouchterlony method using adult antigen, circumoval precipitation and immediate intradermal skin test were observed. A low sensitivity of these serologic tests except for ELISA-egg appears to be primarily due to their inability to detect antibody in the sera from egg-positive infantiles. There was no positive correlation between the absorbance values of these two types of ELISA among the sera isolated from ELISA-positive subjects. Rather, by the reactivity of these sera to egg or adult antigen, they could be divided into two subgroups; one reacted more positively with egg antigen and the other with adult antigen. Moreover, it was confirmed that the sera from young subjects (under 20 years old) appear to be highly reactive to the egg antigen than did aged ones. These data suggest that the ELISA with egg antigen, but not with the adult antigen, appears to be useful for the serological survey of schistosomiasis mansoni in the endemic area of northeast Brazil.

Reinfection after treatment of schistosomiasis: environment or "predisposition"?

Although very efficient for the control of morbidity due to S. mansoni in individual patients, chemotherapy has not proven successful in the management of transmission within hyperendemic areas when used alone, even if repeated at short intervals. Consequently, a great deal of effort has been expended toward immunologic investigation and development of a specific vaccine. Based upon a study of a group of children (5-14 years) from the state of Alagoas, the author demonstrates that the outcome one year after chemotherapy depends essentially on the "risk rating" of the area of domicile. A regression analysis did not reveal significant correlation to neither age, sex or initial egg counts. Although the study was not designed to reveal individual variations in the immune status, it is postulated that putative differences in genetic make-up are irrelevant in terms of large-scale intervention. Since morbidity due to S. mansoni has substantially declined during the last two or three decades, a control policy based on vaccination can only be justified if high levels of protective immunity can be attained. At any rate, such a vaccine will have to be administered in early childhood (preferably below the age of three). It can also be demonstrated that immunization in adolescence or adulthood serves no purpose whatsoever. The author is convinced that environmental intervention, usually dismissed as unrealistic in terms of the developing countries, is not only feasible, if done on a selective basis, but prioritary.

Kinectics of the pulmonary phase of Schistosoma mansoni in mice treated with dexamethasone

In the experimental schistosomiasis mansoni glucocorticoids cause a reduction in the worm burden when administered in the week of infection or, the longest, at the next week. In order to determinate the probable(s) site(s) of reduction of the worm burden, mice were infected with cercariae of LE strain of S. mansoni and dexamethasone was administered daily (50 mg/kg, subcutaneously) starting 1 hour before infection until the eighth day. Mice were sacrificed daily starting on the third day after infection until the ninth day, and schistosomula from lungs were collected. Six weeks after infection, the remaining mice were sacrificed and perfused for adult worm recovery. Analysis of the results showed that the non-treated mice presented larger numbers of lung larvae than the treated ones, and this difference was also found later in the worm burden in the portal system. This difference may reflect the early death of larvae in treated animals, before or after reaching the lungs.

Immunoelectrophoretic study on common antigens of São Lourenço da Mata and Belo Horizonte strains of Schistosoma mansoni adult worms and Biomphalaria snails

Immunoelectrophoretic studies on common antigens were carried out by using rabbits sera immunized against São Lourenço da Mata and Belo Horizonte strains of Schistosoma mansoni adult worms and antigens of Biomphalaria glabrata pigmented (Jaboatão - PE); B. glabrata albino (Belo Horizonte - MG) and B. straminea (São Lourenço da Mata, PE). Furthermore, the reverse approach was proceeded, namely, sera anti Biomphalaria snails produced in rabbits were tested against both strains of Schistosoma adult worm antigens. The analysis of the common antigens between the SLM strains of S. mansoni adult worm and B. glabrata pigmented showed 8 to 9 precipitin bands, 3 bands with B. glabrata albino and only 1 band with B. straminea crude extracts. On the other hand, the BH strain of S. mansoni adult worm antisera produced 6 to 7 bands with B. glabrata pigmented, 5 bands with B. glabrata albino and 1 band with B. straminea antigenic extract. Biomphalaria snails crude extracts were fractionated by Sephadex G-100 column and three fractions were collected from each snail strain. The fractions were tested with anti SLM and BH strains of S. mansoni adult worm sera by immunoelectrophoresis. The common antigens fractionated from Biomphalaria snails crude extracts and those found for both strains of S. mansoni adult worm mostly existed in the first fraction and they were estimated to have molecular weight over 158,000 daltons. In our laboratory, it was found a relationship between the antigenic similarities and experimental infection rates of S. mansoni towards Biomphalaria snails so that more bands were seen with increasing infection rates of S. mansoni.

Biological and morphological characteristics of Schistosoma mansoni from Ribeira Valley, State of São Paulo, Brazil: I - susceptibility of Biomphalaria tenagophila snail to sympatric S. mansoni strain

In the São Paulo State, Brazil, where the Biomphalaria tenagophila is the intermediate host, the Ribeira Valley is an important endemic schistosomiasis mansoni area. During last eleven years there has been intense control measures focusing on schistosomiasis. The efforts have been concentrated in the municipalities of Pedro de Toledo and Itariri. We determined the susceptibility of B. tenagophila to sympatric strain of S. mansoni, both recently isolated from Itariri field. In 1988, this strain was isolated and maintained in the experimental model: Swiss mice - sympatric B. tenagophila. The second generation of the worm was evaluated. The snail were divided in the three groups of 60 snails each. One group was exposed to 1 miracidium and other to 10. The third group was the control. The mortality and the shedding of cercariae were checked during 78 days. After that, the positive snails were observed until they ceased to shed cercariae. The exposed molluscs showed mortality rates of 23% and 31% and infection indexes were of 8% and 60% to 1 and 10 miracidia respectively. The mortality was of 22% in the control group. The periods of shedding cercariae in the two groups were 82 and 104 days. We can conclude that B. tenagophila is an effective intermediate host to the sympatric strain of S. mansoni sympatric strain

Epidemiology of Schistosoma mansoni infection in a low-endemic area in Brazil: clinical and nutritional characteristics

A cross-sectional case-control study designed to evaluate the role of malnutrition in the association between the intensity of Schistosoma mansoni infection and clinical schistosomiasis, was conducted in an area with both low frequency of infection and low morbidity of schistosomiasis in Brazil. Cases (256) were patients with a positive stool examination for S. mansoni; their geometrical mean number of eggs/gram of feces was 90. Controls (256) were a random sample of the negative participants paired to the cases by age, sex and length of residence in the area. The clinical signs and symptoms found to be associated with S. mansoni infection, comparing cases and controls, were blood in stools and presence of a palpable liver. A linear trend in the relative odds of these signs and symptoms with increasing levels of infection was detected. Adjusting by the level of egg excretion, the existence of an interaction between palpable liver and ethnic group (white) was suggested. No differences in the nutritional status of infected and non-infected participants were found.