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.

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.

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.

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.

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.

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.

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.

Attraction of Schistosoma mansoni Sambon, 1907 miracidia to Biomphalaria glabrata (Say, 1818) in the presence of Angiostrongylus costaricensis Morera and Céspedes, 1971 infection.

The attraction exerted by Biomphalaria glabrata infected with Angiostrongylus costaricensis on Schistosoma mansoni miracidia of the BH strain was tested, using a glass apparatus composed by two circular chambers connected to a channel. One mollusk or a sample of a snail conditioning water (SCW) was placed in one of the chambers, randomly selected, and the remaining of the apparatus was filled with chlorine-free water. Ten miracidia were placed in the centre of the channel and their behaviour was observed for 15 minutes. Ten replicates were made for each treatment (snail or SCW), using different specimens of mollusks or different samples of SCW. Mollusks infected with A. costaricensis attracted significantly less S. mansoni miracidia than non-infected B. glabrata. In addition, miracidia were also significantly more attracted to SCW from mollusks infected with A. costaricensis.

Behaviour of albino and melanic variants of Biomphalaria glabrata Say, 1818 (Mollusca: Planorbidae) following infection by Schistosoma mansoni Sambon, 1907.

The behaviour of the albino and melanic variants of Biomphalaria glabrata of Belo Horizonte (MG. Brazil) was studied comparatively, in terms of their respective susceptibilities to infection by Schistosoma mansoni of the same origin, through observation of the elimination of cercariae for a three-month period and the calculation of mortality and infection rates, in control and in infected snails. The number of amoebocytes, granulocytes and hyalinocytes in the circulating hemolymph during different periods of infection was analyzed. The evolution of the infection in the tissues was observed by means of histological cross-sections. The melanic variant showed greater susceptibility to infection and a higher mortality rate. The albino variant showed a higher number of circulating amoebocytes, both granulocytes and hyalinocytes. A higher number of degenerated sporocysts were seen in the histological cross-sections of the albino variant. The results suggest that the melanic variant of B. glabrata was more susceptible to infection by S. mansoni than was the albino variant.