Differences in the number of hemocytes in the snail host Biomphalaria tenagophila, resistant and susceptible to Schistosoma mansoni infection.

The relationships between schistosomiasis and its intermediate host, mollusks of the genus Biomphalaria, have been a concern for decades. It is known that the vector mollusk shows different susceptibility against parasite infection, whose occurrence depends on the interaction between the forms of trematode larvae and the host defense cells. These cells are called amebocytes or hemocytes and are responsible for the recognition of foreign bodies and for phagocytosis and cytotoxic reactions. The defense cells mediate the modulation of the resistant and susceptible phenotypes of the mollusk. Two main types of hemocytes are found in the Biomphalaria hemolymph: the granulocytes and the hyalinocytes. We studied the variation in the number (kinetics) of hemocytes for 24 h after exposing the parasite to genetically selected and non-selected strains of Biomphalaria tenagophila, susceptible or not to infection by Schistosoma mansoni. The differences were analyzed referred to the variations in the number of hemocytes in mollusks susceptible or not to infection by S. mansoni. The hemolymph of the selected and non-selected snails was collected, and hemocytes were counted using a Neubauer chamber at six designated periods: 0 h (control, non-exposed individuals), 2 h, 6 h, 12 h, 18 h and, 24 h after parasite exposure. Samples of hemolymph of five selected mollusks and five non-selected mollusks were separately used at each counting time. There was a significant variation in the number of hemocytes between the strains, which indicates that defense cells have different behaviors in resistant and susceptible mollusks.

Genetic differences between strains of Biomphalaria glabrata (Planorbidae) that are susceptible and unsusceptible to schistosomiasis.

Despite the implementation control programs, schistosomiasis continues to spread throughout the world. Among modern control strategies, vector control is currently being emphasized. Within this context, analysis of the genetic variability of intermediate host snails (Biomphalaria spp) is important because it allows identification of specific sequences of the genome of this mollusk related to susceptibility/resistance to Schistosoma mansoni infection. We investigated Brazilian albino (non-pigmented) and pigmented (wild type) strains of Biomphalaria glabrata; these strains differ in their susceptibility to S. mansoni infection. Genetic variability was studied by RAPD-PCR using different random primers. The electrophoretic patterns resulting from amplification showed specific polymorphic markers for the albino and pigmented strains of B. glabrata. This information will help in the identification and isolation of genes specifically related to susceptibility, demonstrating that RAPD-PCR is an appropriate and efficient methodological approach for analysis of the genetic variability of schistosomiasis vectors.

Schistosome/mollusk: genetic compatibility.

Schistosomiasis remains one of the most prevalent parasitic infections and has significant economic and public health consequences in many developing countries. Economic development and improvement in standard of living in these countries are dependent on the elimination of this odious disease. For the control of Schistosomiasis, understanding the host/parasite association is important, since the host parasite relationship is often complex and since questions remain concerning the susceptibility of snails to infection by respective trematodes and their specificity and suitability as hosts for continued parasite development. Thus, the long term aim of this research is to learn more about the genetic basis of the snail/parasite relationship with the hope of finding novel ways to disrupt the transmission of this disease. In the current research, genetic variability among susceptible and resistant strains within and between Biomphalaria glabrata and B. tenagophila was investigated using RAPD-PCR. The results indicate great genetic variations within the two snail species using three different primers (intrapopulational variations), while specimens from the same snail species showed few individual differences between the susceptible and resistant strains (interpopulational variation).

Susceptibility of Biomphalaria glabrata submitted to concomitant infection with Angiostrongylus costaricensis and Schistosoma mansoni.

The easy adaptation of Angiostrongylus costaricensis, nematode responsible for abdominal angiostrongyliasis to several species of terrestrial and freshwater molluscs and the differences observed in the interactions of trematodes with their intermediate hosts have induced us to study the concomitant infection of Biomphalaria glabrata with Schistosoma mansoni and A. costaricensis. Prior exposure of B. glabrata to A. costaricensis (with an interval of 48 hours), favored the development of S. mansoni, observing higher infection rate, increased release of cercariae and increased survival of molluscs, when compared to molluscs exposed only to S. mansoni. Prior exposure of B. glabrata to A. costaricensis and then to S. mansoni also enabled the development of A. costaricensis since in the ninth week of infection, higher amount of A. costaricensis L3 larvae was recovered (12 larvae / mollusc) while for molluscs exposed only to A. costaricensis, the number of larvae recovered was lower (8 larvae / mollusc). However, pre-exposure of B. glabrata to S. mansoni (with an interval of 24 hours), and subsequently exposure to A. costaricensis proved to be very harmful to B. glabrata, causing extensive mortality of molluscs, reduced pre-patent period to release cercariae and greater recovery of L3 A. costaricensis larvae.

Host-parasite relationship between Biomphalaria amazonica (Paraense, 1966) and Schistosoma mansoni (Sambon, 1907).

Biomphalaria amazonica is a planorbid species considered a potential host of Schistosoma mansoni. It is widely distributed in the Neotropical zone, particularly in the North and Centre-West of Brazil and in the North of Bolivia. The aim of the present study was to determine the host-parasite relationship between B. amazonica and S. mansoni (BH and SJ strains). Specimens of B. amazonica and their snail-conditioned water were examined in terms of their ability to attract miracidia. The infectivity of the mollusks was determined by exposing them to 20 miracidia of both strains. Sporocyst development and amebocyte reactions were studied after each mollusk specimen was exposed to 100 miracidia. Although no cercariae were eliminated, specimens of B. amazonica proved capable of attracting 77% of the miracidia they were exposed to. Viable sporocysts with no amebocyte reaction were found 96 hours after the exposure to miracidia. These results indicate the susceptibility of B. amazonica to the BH and SJ strains of S. mansoni, and therefore demonstrate the importance of this planorbid species as a potential vector of the trematode in the areas where it occurs.

Assessment of the impact of changes in temperature in Biomphalaria glabrata (Say, 1818) melanic and albino variants infected with Schistosoma mansoni (Sambon, 1907).

Fluctuations in population density of planorbid hosts of S. mansoni are influenced by climatic factors. The knowledge about interference from changes in water temperature in these populations is an important aspect of the epidemiology of schistosomiasis. In this experiment, it is explored the influence of different temperatures on the development of Schistosoma mansoni in Biomphalaria glabrata melanic and albino variants. The results indicated an intrinsic relationship between temperature and development of the parasite in the intramollusc phase, independent of the pigmentation of the mantle of the molluscs. The higher the temperature, the shorter the period necessary for the development of the parasite was while the higher the mortality of infected mollusks. It is concluded that, in the presence of climate change, the increasement of temperature in cold and flooded regions may encourage the establishment of new foci of transmission of schistosomiasis by changing the geographic extent and extending the epidemiological transmission potential. In warm climates, higher temperatures, however, could compromise the transmission of the disease because of biological stress suffered by parasite and host. Under these conditions, it can result in the death of the parasite or a change in their ability to infect new host species of molluscs in new areas. Mantle pigmentation patterns in molluscs have not shown significant interference in the development of the parasite.

Behavior of Angiostrongylus costaricensis in planorbids.

Some terrestrial mollusks are natural hosts of Angiostrongylus costaricensis. In the laboratory, this nematode can be maintained in certain planorbids, which are aquatic mollusks and intermediate hosts of Schistosoma mansoni. Mollusks can be infected with Angiostrongylus costaricensis by ingestion of or active penetration by the first-stage larvae. In this work we assessed the ability of Biomphalaria glabrata to attract first-stage larvae of A. costaricensis. Movement of the nematode larvae towards the mollusks was observed after 15 min, 30 min and 1 h. B. glabrata did not attract the first-stage larvae of A. costaricensis in any of the three intervals. The susceptibility of two populations of Biomphalaria tenagophila to infection by A. costaricensis was also determined. One population was genetically selected for the susceptibility to S. mansoni while the other was not. Third-stage larvae were recovered from the snails 30 days after exposure of the two populations to 120 first-stage larvae. All the mollusks were infected. However, a significantly higher number of third-stage larvae were recovered in mollusks not genetically selected.

Influence of saccharose on the development of cercariae from Schistosoma mansoni strains BH and SJ.

The development of cercariae from Schistosoma mansoni strains BH and SJ in Biomphalaria glabrata and Biomphalaria tenagophila treated with saccharose was studied. The molluscs were maintained in dechlorinated tap water containing 0.01% saccharose. After one week of treatment with saccharose, B. glabrata and B. tenagophila were exposed to ten S. mansoni miracidia, from BH and SJ strains respectively. Control snails of both species were maintained in dechlorinated tap water without saccharose and exposed to the same number of miracidia. There was no significant difference between the infection rates of snails treated or not with saccharose. However, the two groups of B. glabrata had significantly greater infection rates than the corresponding B. tenagophila groups. Molluscs treated with saccharose had a lower survival rate, with the greatest mortality occurring immediately before and at the beginning of cercariae release. Treatment with saccharose did not result in the release of more cercariae, but larvae from molluscs so treated showed a greater capacity to penetrate mouse skin, which was attributed to the greater energy supply during larval development in the mollusc.

[Cases of american cutaneous leishmaniasis caused by Leishmania (Viannia) braziliensis in the towns of Cosmópolis and Indaiatuba-region of Campinas, in São Paulo, Brazil]. / Casos de leishmaniose tegumentar americana por Leishmania (Viannia) braziliensis nos Municípios de Cosmópolis e Indaiatuba-região de Campinas, Estado de São Paulo, Brasil.

A study was carried out to identify Leishmania species involved in skin lesions of patients from Cosmópolis and Indaiatuba, State of São Paulo, Brazil. The epidemiological data of cutaneous leishmaniasis in two cities suggested a epidemic situation in 1994. The lesions were clinically characteristic of cutaneous leishmaniasis and five out six patients responded positively to Montenegro's intradermal test. The histopathology of skin lesions were characterized by two patterns: exudative-cellular reaction and exudative granulomatous reaction. The clinical and histopathological parameters suggested Leishmania (Viannia) braziliensis as the possible etiologic agent. In agreement, it was difficult to isolate and maintain the parasite in the laboratory. Characterization by in situ hybridization with kDNA amastigotes from lesions fragments confirmed that Leishmania (Viannia) braziliensis was the parasite responsible for the studied cutaneous lesions.

Biomphalaria tenagophila: genetic variability within intermediate snail hosts susceptible and resistant to Schistosoma mansoni infection.

DNA analysis by molecular techniques has significantly expanded the perspectives of the study and understanding of genetic variability in molluscs that are vectors of schistosomiasis. In the present study, the genetic variability of susceptible and resistant B. lenagophila strains to S. mansoni infection was investigated using amplification of their genomic DNA by RAPD-PCR. The products were analyzed by PAGE and stained with silver. The results showed polymorphism between tested strains with four different primers. We found two bands of 1,900 and 3,420 bp that were characteristic of the susceptible strains with primer 2. The primers 9 and 10 identified a single polymorphic band that was also characteristic of (3,136 and 5,041 bp, respectively) susceptible snails. Two polymorphic bands were detected by primer 15: one with 1,800 bp was characteristic of the resistant strain and the other with approximately equal to 1,700 bp in the susceptible one. These results provide additional evidence showing that the RAPD-PCR technique is adequate for the study of polymorphisms in intermediate hosts snails of S. mansoni. The obtained results are expected to expand the knowledge about the genetic variability of the snails and to permit the future identification of genomic sequences specifically related to the resistance/susceptibility of Biomphalaria to the larval forms of S. mansoni.

[Miracidial attraction by Biomphalaria tenagophila genetically selected for susceptibility]. / Atração miraxonal exercida por Biomphalaria tenagophila selecionada geneticamente para o caráter susceptibilidade.

The attraction of Schistosoma mansoni miracidea by snails genetically selected for susceptibility to infection is considered. Miracidea were exposed to snails or to snail conditioned water in a specially devised three-chamber glass apparatus. Ten miracidea were used for each test and were deposited in the middle chamber (a passage); after 15 minutes, them in each of the number of the three chambers were recorded. In one of the chambers, chosen randomly at each trial, either snails or SCW were used. The snails and the SCW were chosen from either selected snails (highly susceptible) or unselected. The miracidea were of two groups: they came either from susceptible snails in previous generation or were of unselected traits. The results show that only snail generation has importance for the attraction: selected molluscs of susceptible traits do attract the miracidea more.

[Relationship between the pathogenicity of Schistosoma mansoni in mice and the susceptibility of the vector mollusc. I. Cercariae infectivity and worm burden]. / Relação entre a patogenicidade de Schistosoma mansoni em camundongos e a susceptibilidade do molusco vetor. I. Infecciosidade das cercárias e carga de vermes.

The possible influence of the immune mechanisms of the molluscs on the development of the sporocysts and the resultant behavior of the adult worm in the vertebrate host were studied. Two strains of Schistosoma mansoni (BH and SJ) were used. These were genetically selected for their susceptibility and maintained, respectively, in Biomphalaria glabrata and Biomphalaria tenagophila, the natural invertebrate hosts. Experimental groups of mice infected with cercariae proceeding from the two species of molluscs, belonging to generations P, F1, F2, F3 and F4, were formed. The infection rates of the snails, the number of the penetrant cercariae and the worm burden in mice were evaluated. It was concluded that the higher susceptibility of Biomphalaria tenagophila results in a greater ability on the part of the cercarial to develop into adult worms. The higher susceptibility of B. glabrata results in greater power of penetration into mice tegument on the part of the cercariae.

[Relationship between the pathogenicity of Schistosoma mansoni in mice and the susceptibility of the vector mollusk. III. Mortality, body and viscera weight]. / Relacao entre a patogenicidade do Schistosoma manoni em camundongos e a susceptibilidade do molusco vetor. III. Mortalidade, pesos corporal e das visceras.

The relationship between the development of hepatomegaly, splenomegaly, body weight and mortality rate and the degree of susceptibility of Biomphalaria glabrata and B. tenagophila at which infective cercariae developed was studied. The study utilized Swiss mice, SPF, as definitive hosts and populations of snails genetically selected for character susceptibility as intermediate hosts. Low body weight and smaller viscera were observed in infected mice with cercariae originating from snails that showed a high degree of susceptibility. The higher susceptibility of molluscs infected with S. mansoni corresponded to a lower survival of the infected mice. These results lead to the conclusion that the higher degree of adaptation of the parasite to its intermediate hosts, evidenced by the high indexes of susceptibility, leads to different behaviour on the part of this parasite in its definitive host.

Observations on the miraxonal attraction exercised by sexually immature or adult Biomphalaria glabrata infected or not by Schistosoma mansoni.

OBJECTIVE: The influence of age and the presence of secondary sporocysts in the miraxonal attraction exercised by Biomphalaria glabrata on miracidia of Schistosoma mansoni of the BH strain were studied. MATERIAL AND METHOD: A glass apparatus containing two compartments joined by a tube and previously tested in other experiments, was used. Specimens of B. glabrata or its snail conditioned water (SCW) selected before the first oviposition (sexually immature), after the first oviposition (adult), with or without secondary sporocysts, were used to attract the miracidia. RESULTS: It was noted that snails or their SCW containing secondary sporocysts lost the ability to attract miracidia. The sexual maturity of the snail did not influence miraxonal attraction.

[Relationship between pathogenicity of Schistosoma mansoni in mice and the susceptibility of the vector mollusk. IV--Infectiousness of miracidia]. / Relação entre patogenicidade do Schistosoma mansoni em camundongos e susceptibilidade do molusco vector. IV--Infecciosidade dos miracidios.

OBJECTIVE: The infection ability of miracidia of BH and SJ strains of S. mansoni, obtained from mice infected with cercariae taken from Biomphalaria glabrata and Biomphalaria tenagophila, genetically selected for susceptibility is compared with the infection ability of miracidia obtained from mice infected with larvae from non-selected mollusks. MATERIAL AND METHOD: Progeny of S. mansoni resulting from successive infections of selected mollusk sproduced various generations of selected miracidia. Selection of B. glabrata and B. tengophila was carried out by autofertilization of mollusks susceptible to the BH and SJ strains of S. mansoni. Five generations of mollusks (from parental down to F4), were used in the experiment. Tests for the infectiousness of the miracidia used 10 larvae: susceptibility was checked starting on day 30 after infection, for 90 days, through observation for the presence of cercariae. RESULTS: The results showed that susceptibility of the selected mollusks in the face of the respective sympatric strains was not altered by the selection process of S. mansoni. However F4 miracidia of the BH strain were more infectant for non-selected B. glabrate than parental miracidia of the same strain. Miracidia of BH and SJ strains, parental generation, and BH strain, F3 generation, showed the same infectiousness in selected B. glabrata. Nevertheless, these mollusks had distinct infection rates from allopatric selected miracidia (SJ strain, F4 generation). The generation of successive infections of S. mansoni SJ in selected B. tenagophila resulted in the adaptation of the worm strain to the species of mollusk. B. tenagophila was never susceptible to the BH strain, even when selected mollusks and trematodes were employed. The susceptibility/infectiousness of the pair B. tenagophila-SJ S. mansoni strain was only changed by the selection process of the mollusks. CONCLUSION: As non-selected B. glabrata were more intensively infected by selected BH miracidia than by non-selected BH miracidia, one is led to surmise that the greater pathogenicity of S. mansoni from susceptible mollusks implies the greater infection ability of these miracidia.

[Relationship between the pathogenicity of Schistosoma mansoni in mice and the susceptibility of the mollusk vector. II. Number of eggs in feces and number and size of granuloma in visceras]. / Relação entre a patogenicidade do Schistoma mansoni em camundongos e a susceptibilidade do molusco vetor. II. Número de ovos nas fezes e número e tamanho dos granulomas nas vísceras.

The influence of the susceptibility of the vector snails of S. mansoni on the development of the pathogenicity of the worm to the host was studied. Off-spring of snails Biomphalaria glabrata and Biomphalaria tenagophila were used, selected with regard to the susceptibility to S. mansoni of the strains BH and SJ trait, respectively. Parenteral, F1, F2, F3 and F4 generation cercariae were used for the infection of Swiss mice, which were killed eight weeks after infection. The number of eggs in the feces and the number of granulomas in the liver, spleen and intestines were counted. The size of the granulomatous reactions was evaluated. The results led to the conclusion that greater susceptibility of B. tenagophila was associated with a larger egg production in the feces and a higher density of granulomas in the liver. There is a clear inverse relationship between the area of hepatic, splenic and intestinal granulomas and the rate of infection of the snails which served as intermediate hosts for the S. mansoni.

[Miracidial attraction by Biomphalaria straminea, Lymnaea columella and Physa sp on miracidia of Schistosoma mansoni BH strain]. / Atração miraxonal exercida por Biomphalaria straminea, Lymnaea columella e Physa sp, sobre miracídios de Schistosoma mansoni da linhagem BH.

The attraction exercised over Schistosoma mansoni miracidia by Biomphalaria straminea, Lymnaea columella and Physa sp using a specially designed apparatus consisting of two circular glass chambers joined by an open channel were studied. The molluscs or their snail-conditioned water (SCW) was placed in one of the chambers (randomly chosen). In the channel ten miracidia was deposited and the count of miracidia in each of the three compartments (the two chambers and the channel) was recorded during fifteen minutes. Ten replications of each experiment with different specimens of molluscs and miracidia were made. Statistical and ad-hoc exploratory data analysis showed that: a) the three species of molluscs and their SCW attract the miracidia; b) Physa sp attract more miracidia then L. columella. There was an isolated single B. straminea specimen that had a repulsive effect to the miracidia.

Susceptibility of Biomphalaria glabrata submitted to concomitant infection with Angiostrongylus costaricensis and Schistosoma mansoni / Suscetibilidade de Biomphalaria glabrata submetida à infecção concomitante com Angiostrongylus costaricensis e Schistosoma mansoni

Abstract The easy adaptation of Angiostrongylus costaricensis, nematode responsible for abdominal angiostrongyliasis to several species of terrestrial and freshwater molluscs and the differences observed in the interactions of trematodes with their intermediate hosts have induced us to study the concomitant infection of Biomphalaria glabrata with Schistosoma mansoni and A. costaricensis. Prior exposure of B. glabrata to A. costaricensis (with an interval of 48 hours), favored the development of S. mansoni, observing higher infection rate, increased release of cercariae and increased survival of molluscs, when compared to molluscs exposed only to S. mansoni. Prior exposure of B. glabrata to A. costaricensis and then to S. mansoni also enabled the development of A. costaricensis since in the ninth week of infection, higher amount of A. costaricensis L3 larvae was recovered (12 larvae / mollusc) while for molluscs exposed only to A. costaricensis, the number of larvae recovered was lower (8 larvae / mollusc). However, pre-exposure of B. glabrata to S. mansoni (with an interval of 24 hours), and subsequently exposure to A. costaricensis proved to be very harmful to B. glabrata, causing extensive mortality of molluscs, reduced pre-patent period to release cercariae and greater recovery of L3 A. costaricensis larvae.

Resumo A facilidade de adaptação do Angiostrongylus costaricensis, nematódeo responsável pela angiostrongiliase abdominal, a diversas espécies de moluscos terrestres e dulciaquícolas e as divergências observadas nas interações dos trematódeos com seus hospedeiros intermediários nos induziu a estudar a infecção concomitante de Biomphalaria glabrata com Schistosoma mansoni e A. costaricensis. A exposição prévia de B. glabrata ao A. costaricensis (com intervalo de 48 horas), favoreceu o desenvolvimento do S. mansoni observando-se elevação da taxa de infecção, maior liberação de cercárias e maior sobrevivência dos moluscos, quando comparado com os moluscos expostos somente ao S. mansoni. A exposição de B. glabrata previamente ao A. costaricensis e posteriormente ao S. mansoni também facilitou o desenvolvimento do A. costaricensis uma vez que na nona semana de infecção foi recuperada maior quantidade de larvas L3 de A. costaricensis, enquanto nos moluscos expostos somente ao A. costaricensis, o número de larvas recuperadas foi menor . Entretanto a pré-exposição de B. glabrata ao S. mansoni (com intervalo de 24 horas), e posteriormente a exposição ao A. costaricensis mostrou-se muito prejudicial à B. glabrata provocando grande mortalidade dos moluscos, redução do período pré-patente para liberação de cercárias e maior recuperação de larvas L3 de A. costaricensis.

Assessment of the impact of changes in temperature in Biomphalaria glabrata (Say, 1818) melanic and albino variants infected with Schistosoma mansoni (Sambon, 1907) / Avaliação de impacto de alterações na temperatura em Biomphalaria glabrata variantes melânica e albina infectadas com Schistosoma mansoni

Abstract Fluctuations in population density of planorbid hosts of S. mansoni are influenced by climatic factors. The knowledge about interference from changes in water temperature in these populations is an important aspect of the epidemiology of schistosomiasis. In this experiment, it is explored the influence of different temperatures on the development of Schistosoma mansoni in Biomphalaria glabrata melanic and albino variants. The results indicated an intrinsic relationship between temperature and development of the parasite in the intramollusc phase, independent of the pigmentation of the mantle of the molluscs. The higher the temperature, the shorter the period necessary for the development of the parasite was while the higher the mortality of infected mollusks. It is concluded that, in the presence of climate change, the increasement of temperature in cold and flooded regions may encourage the establishment of new foci of transmission of schistosomiasis by changing the geographic extent and extending the epidemiological transmission potential. In warm climates, higher temperatures, however, could compromise the transmission of the disease because of biological stress suffered by parasite and host. Under these conditions, it can result in the death of the parasite or a change in their ability to infect new host species of molluscs in new areas. Mantle pigmentation patterns in molluscs have not shown significant interference in the development of the parasite.

Resumo Flutuações na densidade populacional de planorbídeos hospedeiros do S. mansoni são influenciadas por fatores climáticos. O conhecimento sobre a interferência de alterações na temperatura da água nestas populações é um aspecto importante da epidemiologia da esquistossomose. Neste experimento avaliou-se a influência de diferentes temperaturas no desenvolvimento de Schistosoma mansoni em Biomphalaria glabrata variantes melânica e albina. Os resultados indicaram uma relação intrínseca entre temperatura e desenvolvimento do parasito na fase intramolusco, independente da pigmentação do manto dos moluscos. Quanto mais elevada a temperatura, menor o período necessário para desenvolvimento do parasito e maior mortalidade dos moluscos infectados. Conclui-se que, na presença de alterações climáticas, o aumento da temperatura em regiões frias e alagadas poderá favorecer o estabelecimento de novos focos de transmissão da esquistossomose alterando a extensão geográfica e ampliando o potencial epidemiológico da transmissão. Em regiões de clima quente, o aumento da temperatura, por sua vez, poderá comprometer a transmissão da doença em virtude do estresse biológico sofrido por parasito e hospedeiro. Nestas condições, poderá ocorrer a morte do parasito ou uma alteração na sua habilidade de infectar novas espécies de moluscos hospedeiros em novas áreas. Padrões de pigmentação do manto nos moluscos não demonstraram interferência significativa no desenvolvimento do parasita.

Host-parasite relationship between Biomphalaria amazonica (Paraense, 1966) and Schistosoma mansoni (Sambon, 1907) / Relação parasito-hospedeiro entre Biomphalaria amazonica e Schistosoma mansoni

Abstract Biomphalaria amazonica is a planorbid species considered a potential host of Schistosoma mansoni. It is widely distributed in the Neotropical zone, particularly in the North and Centre-West of Brazil and in the North of Bolivia. The aim of the present study was to determine the host-parasite relationship between B. amazonica and S. mansoni (BH and SJ strains). Specimens of B. amazonica and their snail-conditioned water were examined in terms of their ability to attract miracidia. The infectivity of the mollusks was determined by exposing them to 20 miracidia of both strains. Sporocyst development and amebocyte reactions were studied after each mollusk specimen was exposed to 100 miracidia. Although no cercariae were eliminated, specimens of B. amazonica proved capable of attracting 77% of the miracidia they were exposed to. Viable sporocysts with no amebocyte reaction were found 96 hours after the exposure to miracidia. These results indicate the susceptibility of B. amazonica to the BH and SJ strains of S. mansoni, and therefore demonstrate the importance of this planorbid species as a potential vector of the trematode in the areas where it occurs.

Resumo Biomphalaria amazonica é uma espécie de planorbídeo considerada vetora potencial do Schistosoma mansoni. É amplamente distribuída na zona neotropical, especialmente no Norte e Centro-Oeste do Brasil e Norte da Bolívia. O presente trabalho teve por objetivo estudar a relação parasito-hospedeiro entre B. amazonica e S. mansoni (linhagens BH e SJ). Espécimes de B. amazonica e sua água de condicionamento foram examinados em relação à sua capacidade de atração miraxonal. A infectividade dos moluscos foi testada expondo-os a 20 miracídios de ambas as linhagens. A viabilidade dos esporocistos e o desenvolvimento de reações amebocitárias foram estudados após cada molusco ser exposto a 100 miracídios. Apesar de não eliminarem cercárias, B. amazonica provou ser capaz de atrair 77% dos miracídios a que foram expostos. Esporocistos viáveis sem reação amebócitaria foram encontrados 96 horas após a exposição aos miracídios. Esses resultados indicam a suscetibilidade de B. amazonica às linhagens BH e SJ de S. mansoni e, portanto, demonstram a importância desta espécie de planorbídeo como um vetor potencial do trematodeo na área onde ele ocorre.