Biomphalaria glabrata no Estado do Piauí

É registrado o primeiro encontro do molusco planorbideo Biomphalaria glabrata, hospedeiro intermediário do Schistosoma mansoni, no Estado do Piauí, coletado em vários criadouros na cidade de Parnaíba. O exame de 694 exemplares revelou a presença de formas evolutivas de algumas espécies de trematodeos, mas não de Schistosomatidea. Nenhum caso autoctone de xistosomose foi até agora identificado na população humana da cidade. A presença da B. glabrata em Parnaíba amplia em 20 km para leste a área de sua distribuição na Região Litoral Norte da Grande Região Nordeste do Brasil onde era conhecida até em Avaioses no extremo leste da parte maranhense da referida Região. Outros moluscos também coletados nos mesmos criadouros foram Biomphalaria straminea, Drepanotrema lucidum. D. cimex, D. depressissimum, Physidae e Ampullarriidae.

Orientation to light of juvenile and adult forms of melanic and albino populations of Biomphalaria glabrata (Say, 1818)

The process of light orientation by the snail Biomphalaria glabrata was studied using the selection technique in a Y-shaped aquarium under vertical or horizontal lighting schemes. Snail behavior was measured on the basis of distance (cm) covered per hour, direction of locomotion, and localization of the animal in the aquarium. A comparison was made of the action of the light stimulus on young and adult animals of albino populations from Santa Luzia (State of Minas Gerais, Brazil) and of a melanic population from Touros (State of Rio Grande do Norte) studied in groups and separately. All groups studied were attracted to light. Analysis of the data suggests the exitence of two orientation mechanisms with respect to light in these animals, i.e. high photo-orthokinesia and positive phototaxis, which influence their motion in the environment. This evidence permitted us to discuss features of the distribution dynamics of these mollusks in the environment and their relationship with the larval phases of Schistosoma mansoni, for which they act as intermediated hosts.

Biomphalaria straminea and other planorbids in the Dominican Republic

In addition to previous records of Biomphalaria glabrata in the Dominican Republic, the southern central communities of Haina Arriba and Boca Chica, in the National District, are reported as new localities for that species; other species collected were Biomphalaria obstructa, B. helophila, Drepanotrema lucidum and Lymnaea viatrix. Biomphalaria straminea, a potential vector of Schistosoma mansoni, was found for the first time in the country, in the River Iguamo, just outside of the community of San Pedro de Macorís.

GP38, P28-I and P28-II: candidates for a vaccine against Schistosomiasis

Three antigens protective against Schistosoma mansoni have been extensively characterized. The schistosomulum surface antigen GP38 possesses an immunodominant carbohydrate epitope of which the structure has been defined. Protection can be achieved via the transfer of monoclonal antibodies recognizing the epitope or by immunization with anti-idiotype monoclonal antibodies. The glycan epitope is shared with the intermediate host, Biomphalaria glabrata as well as being present on other molluscs, including the Keyhole Limpet. A group of molecules at 28 kDa were initially characterized in adult worms and shown to protect rats and mice against a challenge infection. One of these molecules, P28-I, was cloned and expressed in E. coli, yeast and vaccinia virus. The recombinant antigen significantly protected rats, hamsters and baboons against a challenge infection. P28-I is a glutathione-S-transferase and the recombinant antigen produced in yeast exhibits the enzyme activity and has been purified to homogeneity by affinity chromatography. A second P28 antigen, P28-II, has also been cloned, fully sequenced and expressed. This recombinant antigen also protects against S. mansoni infection.

Prospects for a nonliving vaccine against Schistosomiasis based on cell-mediated immune resistance mechanisms

We have designed a vaccine model based on induction of cell-mediated immunity and shown that it protects mice against Schistosoma mansoni infection. Mice are immunized by intradermal injection with schistosome antigens plus BCG. Resistance is dependent on the route of antigen presentation and the adjuvant chosen. The pattern of resistance correlates with sensitization of T lymphocytes for production of gamma interferon, a macrophage activating lymphokine that stimulates the cellular effector mechanism of protection. Purified schistosome paramyosin, a muscle cell component present in soluble parasite antigenic preparations, is immunogenic for T lymphocytes and induces resistance when given intradermally with BCG. It is likely that this protein, and possibly other soluble molecules that are released by the parasites of a challenge infection, induce a cellular inflammatory response resulting in larval trapping and/or killing by activated macrophages. These results verify the feasibility of a vaccine against schistosomiasis based on induction of cell-mediated immune resistance mechanisms.

Drug resistance in Schistosomiasis: a review

Drug resistance associated with the treatment of human schistosomiasis appears to be an emerging problem requiring more attention from the scientific community than the subject currently receives. Drug-resistant strains of Schistosoma mansoni have been isolated by various investigators as a result of laboratory experimentation or from a combination of field and laboratory studies. Review of this data appears to indicate that the lack of susceptibility observed for some of the isolated strains cannot be ascribed solely to previous administration of antischistosome drugs and thus further studies are required to elucidate this phenomena. Strains of S. mansoni have now been identified from Brazil which are resistant to oxamniquine, hycanthone and niridazole; from Puerto Rico which are resistant to hycanthone and oxamniquine; and from Kenya which are resistant to niridazole and probably oxamniquine. Strains derived by in vitro selection and resistant to oxamniquine and possibly to oltipraz are also available. All of these strains are currently maintained in the laboratory in snails and mice, thus providing for the first time an opportunity for indepth comparative studies. Preliminary data indicates that S. haematobium strains resistant to metrifonate may be occurring in Kenya. This problem could poise great difficulty in the eventual development of antischistosomal agents. Biomphalaria glabrata from Puerto Rico and Brazil were found to be susceptible to drug-resistant S. mansoni from each country.

Anti-schistosomal drugs: observations on the mechanism of drug resistance to hycanthone, and on the involvement of host antibodies in the mode of action of praziquantel

This paper reports recent observations from our laboratory dealing with the anti-schistosome drugs hycanthone (HC) and praziquantel (PZQ). In particular, we discuss a laboratory model of drug resistance to HC in Schistosoma mansoni and show that drug sensitive and resistant lines of the parasite can be differentiated on the basis of restriction fragment length polymorphisms using homologous ribosomal gene probes. In addition, we summarize data demonstrating that effective chemotherapy of S. mansoni infection with PZQ in mice requires the presence of host anti-parasite antibodies. These antibodies bind to PZQ treated worms and may be involved in an antibody-dependent cellular cytotoxicity reactions which result in the clearance of worms from the vasculature.

Decay accelerating factor (DAF) as the host antigen with protective activity to complement killing of schistosomula

The acquisition of host antigens by Schistosoma mansoni was studied by evaluating the resistance of schistosomula to the complement attack mediated by lethal antibody. Schistosomula cultured for 24 hours with intact human erythrocytes (N-HuE) or ghosts of any type of ABO or Rh blood group, showed a marked resistance to complement damage. Sheep red blood cells, pronase-treated N-HuE or erythrocytes from patients with paroxysmal nocturnal hemoglobinuria, which are complement-sensitive cells, were unable to protect schistosomula. Schistosomula protected by N-HuE became again susceptible to complement killing after incubation with a monoclonal antibody anti-DAF. These results indicate that, in vitro, host DAF from N-HuE can be acquired by schistosomula surface in a biological active form that protects the parasite from the complement lesion.

Influence of experimental illumination and seasonal variation on crossbreending mating in the snail Biomphalaria Glabrata

The crossbreeding activities of the Schistosoma mansoni vector snail Biomphalaria glabrata were counted in a laboratory aquarium throughout the year under two regimes of 12h light: 12h dark from 7 A., M. to 10 P. M. Mating increased significantly in Authmn and Winter and just missed a significant inverse correlation with temperature and a direct one with locomotion. Other similar experiments were carried out to compare mating under various ilumination conditions in complete daily cycle measurements. Mating counts decreased under the regimes which submited snail to a total exposure of 12h light and 12 dark during a daily cycle in the following sequence: 12h light: 12h dark alternating hourly with light gradient, 12h light: 12h dark, 1h light: 1h dark and 12h dark: 12h light. Under two constant illuminations, the mating scored less than under the previous conditions, except under 12h light. Under darkeness the mating count was lower than light conditions. There was no way to differentiate the night and day rhythms of mating on different days in each regime, except for mating under 12h light: 12 dark alternating with light gradient, constant dark and 12h dark: 12h light conditions. Mating increased in certain light and temperature conditions, in wich the intensities, should have an optimum value.

Study of a population of Biomphalaria tenagophila (Orbigny, 1835) and of schistosomiasis transmission in "Alto da Boa Vista", Rio de Janeiro

The present study was performed using data from a Biomphalaria tenagophila population located in a water cress garden in the Alto da Boa Vista region representing an isolated focal point of schistosomiasis in the city of Rio de Janeiro. The density and age structure of this B. tenagophila population and its rate of intection by Schistosoma mansoni were studied for a period of 15 months. The snail population showed seasonal variation in density, with a decrease in number of individual at the begining of the rainy season. At the end of this season, the population consisted mainly of adults (92.8% in May 1985 and 82.8% in April 1986). The population growth curve was logistic and of sigmoidal configuration. Shiscotoma mansoni cercariae were eliminated over a short period of time (March, April and May 1986). The release of cercariae of S. mansoni and of birds seems to depend on environmental temperature, which during certain months would show a daily variation of up to 13ºC, with the lower thermal limit approaching the limit value for sporocyte development.

Dispersão de Biomphalaria straminea no estado de Sergipe: um estudo comparativo com dezenove anos de intervalo

No presente trabalho, realizado no Estado de Sergipe, procurou-se determinar a distribuição geográfica e as interrelações entre populações naturais de duas espécies do gênero Biomphalaria, os caramujos vetores do Schistosoma mansoni no nordeste do Brasil. Dados coletados em 1969 mostraram que B. straminea, com uma única exceção, estava limitada à região semi-árida, enquanto B. glabrata habitava a região litoral/mata, ambas no Estado de Sergipe. Esta distribuição espacial parecia indicar que as espécies acima denominavam territórios exclusivos. Coletas de caramujos feitas em 1988, nas mesmas 37 localidades pesquisadas anteriormente (1969), evidenciaram que B. straminea havia invadido territórios previamente ocupados por B. glabrata. Estes resultados sugerem que as duas espécies estão interagindo em processo de deslocamento competitivo. Foram ainda determinadas as taxas de infecção natural dos caramujos, assim como foram registrados alguns aspectos ecológicos de seus criadouros.

The immune-dependence of chemotherapy in experimental schistosomiasis

Experimental evidence indicates that immune effector mechanisms can enhance the activity of schistosomicidal drugs. Praziquantel, oxamniquine, hycanthone and antimony were less effective against Schistosoma mansoni infections in mice immunosuppressed by T cell-deprivation, than against comparable infection in normal mice. The schistosomicidal activities of praziquantel, oxamniquine and antimony have been experimentally enhanced by the synergistic action of immune sera. In passive serum transfer experiments a s. mansoni antigen of Mr 27 kD with non-specific esterase activity was identified as a potentially sensitive target for the antibodies that interact with praziquantel. Indirect immunofluorescence indicated that this antigen was exposed on the worm surface as a result of praziquantel treatment.

Biological control of Biomphalaria tenagophila (Mollusca, Planorbidae), a schistosomiasis vector, using the fish Geophagus brasiliensis (Pisces, Cichlidae) in the laboratory or in a seminatural environment

In order to investigate a possible method of biological control of schistosomiasis, we used the fish Geophagus brasiliensis (Quoy & Gaimard, 1824) which is widely distributed throughout Brazil, to interrupt the life cycle of the snail Biomphalaria tenagophila (Orbigny, 1835), an intermediate host of Schistosoma mansoni. In the laboratory, predation eliminated 97.6% of the smaller snails (3-8 mm shell diameter) and 9.2% of the larger ones (12-14 mm shell diameter). Very promising results were also obtained in a seminatural environment. Studies of this fish in natural snail habitats should be further encouraged.

Action of colchicine on hepatic schistosomal granuloma

Amorphous material and altered collagen fragments within dilated secretory vesicles and cisternae of fibroblast cytoplasm were the main ultrastructural changes seen in hepatic periovular granulomas formed in mice infected with Schistosoma mansoni and treated with colchicine. Despite promoting ultrastructural changes in the fibroblasts found in hepatic periovular granulomas, colchicine administration to infected mice did not significantly change the light microscopic appearance of the hepatic schistosomal lesions, did not diminish the amount of total hepatic collagen, and did not change the collagen isotypes in the granulomas, as observed after a comparative study with non-colchicine treated infected control mice. When administered to mice two weeks after curative treatment of schistosomiasis with praziquantel, colchicine did not seem to increase extracellular collagen degradation or to induce a more rapid resorption of hepatic periovular granulomas, although still promoting ultrastructura alterations in fibroblasts.

Potential schistosome-vector snails and associated trematodes in ricefields of Corrients province, Argentina: preliminary results

Considering the possibility of introduction of schistosomiasis mansoni into Argentina as a consequence of dam construction on the Rio De La Plata basin, preliminary studies have been carried out on agrosystems such as ricefields in Corrientes province with the following purposes: 1) to survey and estimate the relative abundance of planorbids and identify potential vector species; 2) to identify environmental factors capable of influencing Biomphalaria population dynamics; and 3) to find out snail-parasite associations and estimate snail infection rates in order to detect possible competitive interactions between larval stages of native trematodes that could be used in biological control of Schistosoma mansoni. Three potential schistosome vectors were detected in ricefields, namely Biomphalaria straminea, B. tenagophila and B. peregrina, although B. orbignyi, a species refractory to infection with S. mansoni, proved the most frequent and abundant. Positive correlations (P<0.05) were found between Biomphalaria abundance and some environmental parameters: conductivity, hardness, calcium, nitrites plus nitrates, ammonium and bicarbonates. Water temperature correlation was negative (P<0.05). No correlation (P>0.05) was found in total iron, phosphates (SRP), pH and soil granulometry. Echinocercariae developed from rediae and belonging to Petasiger sp., Paryphostomum sp., and other undetermined species were found.