Environmental epidemiology of intestinal schistosomiasis in Uganda: population dynamics of biomphalaria (gastropoda: planorbidae) in Lake Albert and Lake Victoria with observations on natural infections with digenetic trematodes.

This study documented the population dynamics of Biomphalaria and associated natural infections with digenetic trematodes, along the shores of Lake Albert and Lake Victoria, recording local physicochemical factors. Over a two-and-a-half-year study period with monthly sampling, physicochemical factors were measured at 12 survey sites and all freshwater snails were collected. Retained Biomphalaria were subsequently monitored in laboratory aquaria for shedding trematode cercariae, which were classified as either human infective (Schistosoma mansoni) or nonhuman infective. The population dynamics of Biomphalaria differed by location and by lake and had positive relationship with pH (P < 0.001) in both lakes and negative relationship with conductivity (P = 0.04) in Lake Albert. Of the Biomphalaria collected in Lake Albert (N = 6,183), 8.9% were infected with digenetic trematodes of which 15.8% were shedding S. mansoni cercariae and 84.2% with nonhuman infective cercariae. In Lake Victoria, 2.1% of collected Biomphalaria (N = 13,172) were infected with digenetic trematodes with 13.9% shedding S. mansoni cercariae, 85.7% shedding nonhuman infective cercariae, and 0.4% of infected snails shedding both types of cercariae. Upon morphological identification, species of Biomphalaria infected included B. sudanica, B. pfeifferi, and B. stanleyi in Lake Albert and B. sudanica, B. pfeifferi, and B. choanomphala in Lake Victoria. The study found the physicochemical factors that influenced Biomphalaria population and infections. The number and extent of snails shedding S. mansoni cercariae illustrate the high risk of transmission within these lake settings. For better control of this disease, greater effort should be placed on reducing environmental contamination by improvement of local water sanitation and hygiene.

Molluscicidal and ovicidal activities ofplant extracts of the Piperaceae onBiomphalaria glabrata (Say, 1818)

Schistosomiasis is a tropical disease caused by Schistosoma and occurs in 54countries, mainly in South America, the Caribbean region, Africa and the easternMediterranean. Currently, 5 to 6 million Brazilian people are infected and 30,000are under infection risk. Typical of poor regions, this disease is associated withthe lack of basic sanitation and very frequently to the use of contaminated water in agriculture, housework and leisure. One of the most efficient methods of controlling the disease is application of molluscicides to eliminate or to reduce the population of the intermediate host snail Biomphalaria glabrata. Studies on molluscicidal activity of plant extracts have been stimulated by issues such as environmental preservation, high cost and recurrent resistance of snails tosynthetic molluscicides. The aim of this study was to determine the molluscicideaction of extracts from Piperaceae species on adult and embryonic stages ofB. glabrata. Fifteen extracts from 13 Piperaceae species were obtained from stems, leaves and roots. Toxicity of extracts was evaluated against snails at two different concentrations (500 and 100ppm) and those causing 100% mortality at 100ppm concentration were selected to obtain the LC90 (lethal concentration of 90% mortality). Piper aduncum, P. crassinervium, P. cuyabanum, P. diospyrifolium and P. hostmannianum gave 100% mortality of adult snails at concentrations ranging from 10 to 60 ppm. These extracts were also assayed on embryonic stages of B. glabrata and those from P. cuyabanum and P. hostmannianum showed 100%ovicidal action at 20ppm.

Distribuição e diversidade de espécies do gênero Biomphalaria em microrregiões localizadas no Médio Paranapanema, São Paulo, SP, Brasil / Diversity and distribution of the Biomphalaria species in the middle reaches of the Paranapanema River, São Paulo, SP, Brazil

The predominant landscape in the studied region, composed by the Paranapanema and Pardo rivers, has been significantly affected by human interference in order to create extensive artificial irrigation ditches for agriculture. These environments are subject to drastic variations in water supply whereby draughts are created what bears a drastic populational fluctuation. The composition of schistosomiasis-associated planorbid fauna in Ourinhos and Ipauçu herein presented corroborate previous malacological surveys, which incriminates Biomphalaria. glabrata (Say, 1818) as the predominant species mainly at the Ourinhos micro-regions. At this site the snail distribution might be linked to the composition of deposited sediments in the hydrographic basin. Data from Ipauçu, a collection site that is only 30 km from Ourinhos, indicates absence of B. glabrata, and predominance of B. tenagophila (Orbigny, 1835). Despite closeness, the micro-regions show important differences in values of diversity index, indicating a heterogeneous distribution of Biomphalaria species.

Foram estudadas a diversidade e a abundância de espécies do gênero Biomphalaria em córregos próximos aos Rios Paranapanema e Pardo (São Paulo, SP, Brasil), em locais antigamente associados à transmissão do Schistosoma mansoni, sujeitos ainda a drásticas variações na disponibilidade de água. Os dados confirmam a predominância de Biomphalaria glabrata (Say, 1818) em córregos do município de Ourinhos, localizados nas margens do Rio Pardo e do Rio Paranapanema. Em Ipauçu, distante 30 km de Ourinhos, a predominância de Biomphalaria tenagophila (Orbigny, 1835) é acompanhada da ausência de B. glabrata. Foram estimados os índices de Diversidade e Dominância de Simpson, que evidenciam uma distribuição variada, provavelmente associada com o substrato aquático onde vivem os caramujos.

Trade-offs in the evolution of virulence in an indirectly transmitted macroparasite.

The adaptive trade-off theory for the evolution and maintenance of parasite virulence requires that virulence be genetically correlated with other fitness characteristics of the parasite. Many theoretical models rely on a positive correlation between virulence and transmissibility. They assume that high parasite replication rates are associated with a high probability of transmission (and, hence, increased parasite fitness), but also with high levels of damage to the host (high virulence). Schistosomes are macroparasites with an indirect life cycle involving a mammalian and a molluscan host. Here we demonstrate, through the development of five substrains, a genetic basis for schistosome virulence. We used these substrains further in order to investigate the presence of parasite fitness traits that were genetically correlated with virulence. High virulence in the (mouse) definitive host was, as predicted, positively correlated with parasite replication. In contrast, in the (snail) intermediate host high virulence was associated with low parasite replication rates. Variation in infectivity to and parasite replication in the definitive host was suggested as a compensating mechanism for the maintenance of virulence in the snail host. This is the first report of a trade-off in parasite reproductive success across hosts in an indirectly transmitted macroparasite.

Suscetibilidade de Biomphalaria tenagophila de Bragança Paulista à cepa de Schistosoma mansoni / Suscetibility of Biomphalaria tenagophila of Bragança Paulista town to infection with Schistosoma mansoni

Estudou-se a suscetibilidade de Biomphalaria tenagophila da regiao de Bragança Paulista (SP) à infecçao progressiva pelo Schistosoma mansoni, cepa SJ. Os resultados pelo Schistosoma mansoni, cepa SJ. Os resultados mostram-se positivos para a infecçao com 100 miracídios. Apenas 50 por cento dos moluscos foram positivos durante 21 dias. Com esses resultados pode-se afirmar que na regiao de Bragança Paulista, com o possível aumento de migraçao de indivíduos da zona endêmica, estamos sujeitos ao aparecimento de casos positivos de esquistossomose adquiridos na regiao.

Aspectos da Biologia da Reprodução e Espermatogênese de Biomphalaria Tenagophila / Aspects of reprodutive biology and spermatogenesis on Biomphalaria Tenagophila

Os moluscos do gênero Bimomphalaria são hermafroditas simultâneos podendo se reproduzir por fecundação cruzada ou por autofecundação. No entanto, segundo observações de Paraense (1955), em Australorbis glabratus (=Biomphalaria glabrata), o modo de reprodução preferencial nesta espécie seria a fecundação cuzada, que garantiria a manutenção da variabilidade de genética. Em contraposição, a autofecundação seria uma estratégia reprodutiva menos freqüente utilizada apenas na colonização de novos habitats. No entanto não se conhece, até agora, qualquer mecanismo que impeça a prática da autofecundação. A partir destas informações elaboramos dois experimentos a fim de comparar os dois modos de reprodução em Biomphalaria tenagophila, baseados na hipotese de que o rendimento reprodutivo da espécie seria superior em fecundação cruzada, refletindo uma vantagem adaptativa condizente com sua maior freqüência de ocorrência. No primeiro experimento analisamos o tamanho e idade na maturação sexual, fecundidade e fertilidade dos ovos em gerações sucessivas de autofecundação, submetidas portanto a endocuzamento prolongado. No segundo experimento as mesmas variáveis foram observadas em animais acasalados. Os resultados mostram que o rendimento reprodutivo em fecundação cruzada não é superior ao de autofecundação, no entanto, progênie dos albinos acasalados à pigmentados resultou predominantemente de fecundação cruzada. Sugerimos que a autofecundação, embora facultativa, ocora com maior freqüência na natureza do que até agora suposto. No estudo da espermatogênese de Biomphalaria tenagophila foi confirmado que o número haplóide básico da espécie é n=18, e, dada a boa qualidade técnica das preparações cromossômicas pudemos caracterizar um mior número de fases espermatogenéticasdo que até agora descritas na literatura. Observamos também, em animais dessecados um desaceleramento gradativo do processo meiótico em função do tempo de dessecação à que foram submetidos aos animais.