Diagnostic markers in schistosomiasis

In the present paper a brief overview will be given of the recent progress and trends in assaying diagnostic markers in schistosomiasis; only markers of the humoral immunological system and biochemical markers will be discussed, as markers for cellular immunological reactivity will be discussed by other authors. The following diagnostic markers will be reviewed: markers for infection, markers for immunity and markers for morbidity.

Factors conditioning the habitat and the density of Biomphalaria tenagophila (Orbigny, 1835) in an isolated schistosomiasis focus in Rio de Janeiro city

The present work was carried out in a watercress garden in Alto da Boa Vista, in the city of Rio de Janeiro, Brazil. The investigation was carried out in two phases. The first one (1985-86) involved the sampling of Biomphalaria tenegophila in two areas to determine its relative populational densities. The results showed that the populations presented similar densities and dynamics. The second phase (1988-89) involved the study of the influence of some environmental factors on the establishment of B. tenagophila in watercress garden. Two factors were identified as responsible for the establishment of B. tenagophila in the garden: (1) the quality of the water entering the irrigation system, to which domestic sewage is added, and (2) alterations in the nature of the substrate, due to inadequate fertilization techniques, which employ organic matter from adjacent pigsties. Aquatic plants and hydrological parameters of the irrigation system were subsidiary factors to the establishment of B. tenagophila in the garden.

Intestinal protein absorption in malnourished mice with acute schistosomiasis mansoni

Intestinal protein absorption was studied in undernourished albino Swiss mice with acute schistosomiasis mansoni. Undernutrition was induced by feeding mice with the Regional Basic Diet (RBD) ingested by human populations in Northeast Brazil, an experimental model previously developed in our laboratory. Weaning mice were infected with 40 cercariae and compared to undernourished non-infected mice and/or to infected mice fed a balanced control diet. Apparent and True Protein Absorption Coefficients were determined by nitrogen balance during five consecutive days ending at the 63rd day of the trial (acute phase of murine schistosomiasis). Fecal metabolic nitrogen (FMN) was determined after administration of a non-protein diet and was also calculated through linear regression. Our results showed a reduced protein absorption in non-infected RBD-fed mice as compared to mice fed a casein control diet. Infection with Schistosoma mansoni had apparently no effect on intestinal protein absorption in well-nourished mice. However, infection seemed to interfere with protein absorption in under-nourished animals, since the lowest absorption ratios have been detected among RBD-fed infected mice. A brief discussion is made on the advantages of using the method of linear regression for the determination of FMN.

Schistosomiasis mansoni in the region of the Triângulo Mineiro, State of Minas Gerais, Brazil

In order to reevaluate the possible presence of schistosomiasis mansoni in the Triângulo Mineiro, one of the areas of the State of Minas Gerais where this parasite is not commonly found, malacological survey and fecal examinations were undertaken in the region between October 1990 and June 1992. A sample of 7,032 1st grade school children from 29 counties had their feces examined using the Kato-Katz method. Amongst the children examined, two from Planura and one from each countie of Capinópolis, Conceição das Alagoas, Uberaba, Uberlândia, Prata and Gurinhatã were positive for Schistosoma mansoni. None of the children were identified as being autoctonous cases. In the malacological survey, 5,406 planorbid snails were examined. The specimens were identified morphologically and examined for S. mansoni by squashing between glass plates. The species were identified as Biomphalaria tenagophila in three counties, as B. straminea in ten and B. intermedia in 16. No snails were found in eight other counties studies. The snails were found to be negative for S. mansoni. The presence of intermediate hosts for S. mansoni, associated with parasitized individuals emphasizes the necessity of epidemiological surveillance for schistosomiasis in the region of Triângulo in the State of Minas Gerais.

Ultrasonography in Schistosomiasis in Africa

Approximately 50 publications have become available in the international literature on ultrasonography in schistosomiasis in Africa. Geographically these cover Congo, Egypt, Kenya, Mali, Mauritius, Niger, Senegal, Sudan, Tanzania and East African Islands as well as Zimbabwe. Further studies are ongoing in many countries, such as Burundi, Ghana, Madagaskar and Uganda. It was shown that ultrasonography is useful in the detection of morbidity induced by schistosomiasis on an individual basis and on the community level. There is indication for varying morbidity patterns in different African foci. Post-treatment monitoring has provided evidence for reversibility of pathological lesions induced by Schistosoma (S.) haematobium and S. mansoni, even though evidence for reversibility of periportal fibrosis in adults is not yet satisfactorily substantiated. A standardized set of criteria for ultrasonographical observations has been worked out and is presently in the process of being refined. It is thus hoped that standardization will contribute to render studies in different endemic settings comparable on a global basis.

Determination and control of schistosomiasis

The subject of this conference reflects the scientific community's interest in seeking to understand the complex causal web whose various social, economic, and biological components interact in the production and reproduction of schistosomiasis and its control in relation to community participation. From the onset, the author stresses the impossibility of dealing separately with community participation, as if social components were just one more "weapon" in the arsenal for schistosomiasis control. This study begins with a brief historical review of the 71 years of control activities with this endemic disease, stressing the enormous efforts and huge expenditures in this field vis-à-vis the limited results, despite the extraordinary technological development of specific, classical control inputs such as new treatment drugs and molluscicides. The article then discusses the various strategies used in control programs, emphasizing ideological consistencies and contradictions. Interactions at the macro and micro levels are discussed, as are the determinants and risk factors involved in producing the disease's endemicity. Unequal occupation of space leaves the segregated portion of the population exposed to extremely favorable conditions for transmission of the disease. This raises the issue of how to control an endemic disease which is so closely linked to the way of life imposed on the population. The study challenges the classical control model and suggests an alternative model now undergoing medium-term investigation in the States of Espirito Santo, and Pernambuco, Brazil. The author concludes that we do not need new strategies, but a new control model, contrary to the prevailing classical model in both concept and practice. From the conceptual point of view, the new model mentioned above is different from others in that schistosomiasis control is seen from a social perspective stressing the population's accumulated knowledge in addition to the building of shared knowledge. The model's praxis has the following characteristics: (1) it is integrated with and financed by research agencies and health services; (2) it operates at the local health services level; (3) use of molluscicides has been eliminated; (4) emphasis is given to individual medical treatment and improvement of sanitary conditions.

Treatment of schistosomiasis: gathering stones together

In this paper the treatment of schistosomiasis is examined under the following headings: cercarial dermatitis, Katayama fever, schistosomiasis in the immunosuppressed host and treatment of therapeutic failures.

Molluscicide control of snail vectors of schistosomiasis

A review of the methodology recommended by the World Health Organization for the use of molluscicides for the control of snail vectors of schistosomiasis is presented. Discussion of the principle molluscicides used, their advantages and disadvantages, the techniques and equipment required for their application and evaluation of effect as well as the biological control of snails is included.

Extramedullary hematopoiesis in murine schistosomiasis mansoni

During Schistosoma mansoni infection, there is morphological evidence of involvement of various hematopoietic growth factors, which cause eosinophil, neutrophil, megakaryocytic and erythroid extramedullary foci in the liver, lymph nodes and omental and mesenteric milky spots. While the eosinophil metaplasia in the periphery of hepatic granulomas roughly reproduced the intensity of the medullary eosinopoiesis, the neutrophil metaplasia, on the contrary, was more intense during the period of neutrophil depression in the bone marrow. This fact suggests that extramedullary hematopoietic foci are locally regulated, and amplify and/or compensate the systemic hematopoietic response during the infection.

The snail hosts of schistosomiasis: some evolutionary and ecological perspectives in relation to control

Despite opportunities for radiation provided by spatio-temporal isolation, the basic morphological plan of pulmonate snails has remained conservative. In consequence of the resulting dearth of morphological characters and their plasticity, there is a case for using biochemical characters such as exogenous chemicals released by the snails (e.g. amino acids) and their chemoreception niche as taxonomic aids to classify snails of medical importance. As these same chemicals are used by snails to distinguish conspecifics they could also be used as "environmental antibodies" in controlled release formulations (CRF's) designed to remove target snails in a specific, cost-effective and ecologically acceptable manner. The snails, surface-living bacteria, algae and macrophytic plants are considered as co-evolved, interactive modular systems with strong mutualistic elements. Recently, anthropogenic perturbations such as deforestation, and damming of flowing waters, have benefited these modules whereas others such as river canalization, acid deposition, accumulation of pesticide residues and eutrophication have harmed them. Research is needed to elucidate the factors which limit the growth of snails in primitive habitats, uninfluenced by man, as well as in those subject to harmful anthropogenic factors. The understanding thus gained could be applied to develop cost-effective primary health care strategies to reduce or prevent transmission of schistosomiasis and other water related diseases.

Opportunities and constraints in schistosomiasis vaccine development: infection characteristics and industry realities

The notes provided in this article relate to two components of the development of vaccines against schistosomiasis: (1) The characteristics of schistosome infections (eg. features of the schistosome life cycle), and the parasite itself, that have implications for vaccination strategies; (2) The characteristics of the biopharmaceutical industry that have implications for product development. As will be seen, these two topic areas are not vastly disparate.

Schistosomiasis vaccine development: approaches and prospects

Mounting evidence for acquired immunity to schistosomiasis in humans supports the case for immunological intervention. On the other hand, rapid reinfection poses a threat to younger age groups due to the slow maturation of natural resistance. However, rational approaches, based on advances in immunology and molecular biology, have substantially increased the odds of producing an effective vaccine. Since the parasite cannot replicate in the human host and serious morbidity generally occurs only after a relatively long period of heavy worm burden, complete protection against infection is not essential. The chances of success would increase if more than one of the various host/parasite interphases were targeted, for example reducing morbidity through decreased worm loads as well as through suppression of egg production. Several promising schistosome antigens have now reached an advanced phase of development and are currently undergoing independent confirmatory testing according to a standardized protocol. A few molecules are being contemplated for scaled-up production but, so far, only one has reached the stage of industrial manufacture and safety testing. Since schistosomiasis cannot realistically be controlled by a single approach, vaccination is envisaged to be implemented in conjunction with other means of control, notably chemotherapy.

Health education, public information, and communication in schistosomiasis control in Brazil: a brief retrospective and perspectives

In recent years, the strategy for the control of schistosomiasis has placed increased emphasis on the role of health education, public information, and communication. This should, not only bring about specific changes in behavior aiming at disease prevention, but also stimulate participation of the community in health programs. Beyond this, it is desirable that both community members and researchers should seek better life conditions through a transformative social action. The present paper addresses these concerns; first, by critically reviewing some health education programs that were developed in Brazil, and, secondly, by analyzing and suggesting ways to improve this area.

Development of a vaccine strategy against human and bovine schistosomiasis: background and update

Schistosomiasis is a chronic and debilitating parasitic disease that affects over 200 million people throughout the world and causes about 500,000 deaths annually. Two specific characteristics of schistosome infection are of primordial importance to the development of a vaccine: schistosomes do not multiply within the tissues of their definitive hosts (unlike protozoan parasites) and a partial non-sterilizing immunity can have a marked effect on the incidence of pathology and on disease transmission. Since viable eggs are the cause of disease pathology, a reduction in worm fecundity whether or not accompanied by a reduction in parasite burden is a sufficient goal for vaccine induced immunity. We originally showed that IgE antibodies played in experimental models a pivotal role for the development of protective immunity. These laboratory findings have been now confirmed in human populations. Following the molecular cloning and expression of a protein 28 kDa protein of Schistosoma mansoni and its identification as a glutathion S-transferase, immunization experiments have been undertaken in several animal species (rats, mice, baboons). Together with a significant reduction in parasite burden, vaccination with Sm28 GST was recently shown to reduce significantly parasite fecundity and egg viability leading to a decrease in liver pathology. Whereas IgE antibodies were shown to be correlated with protection against infection, IgA antibodies have been identified as one of the factors affecting egg laying and viability. In human populations, a close association was found between IgA antibody production to Sm28 GST and the decrease of egg output. The use of appropriate monoclonal antibody probes has allowed the demonstration that the inhibition of parasite fecundity following immunization was related to the inhibition of enzymatic activity of the molecule. Epitope mapping of Sm28 GST has indicated the prominent role of the N and C terminal domains. Immunization with the corresponding synthetic peptides was followed by a decrease of 70% of parasite fecundity and egg viability. As a preliminary step towards phase I human trials, vaccination experiments have been performed in cattle, a natural model for Schistosoma bovis. Vaccination of calves with the S. bovis GST has led to a reduction of ever 80% of egg output and tissue egg count. Significant levels of protection were also observed in goats after immunization with the recombinant S. bovis GST. Increasing evidence of the participation of IgA antibodies in protective immunity has prompted us toward the development of mucosal immunization. Preliminary results indicate that significant levels of protection can be achieved following oral immunization with live attenuated vectors or liposomes. These studies seem to represent a promising approach towards the future development of a vaccine strategy against one of major human parasitic diseases.

Vaccination against schistosomiasis and fascioliasis with the new recombinant antigen Sm14: potential basis of a multi-valent anti-helminth vaccine?

Molecular cloning of components of protective antigenic preparations have suggested that related parasite fatty acid binding proteins could form the basis of the well documented protective, immune cross reactivity between the parasitic trematode worms Fasciola hepatica and Schistosoma mansoni. We have now confirmed the cross protective potential of parasite fatty acid binding proteins and suggest that it may be possible to produce a single vaccine that would be effective against at least two parasites, F. hepatica and S. mansoni of veterinary and human importance respectively.