Origin and diversification of the human parasite Schistosoma mansoni.

Schistosoma mansoni is the most widespread of the human-infecting schistosomes, present in 54 countries, predominantly in Africa, but also in Madagascar, the Arabian Peninsula, and the Neotropics. Adult-stage parasites that infect humans are also occasionally recovered from baboons, rodents, and other mammals. Larval stages of the parasite are dependent upon certain species of freshwater snails in the genus Biomphalaria, which largely determine the parasite's geographical range. How S. mansoni genetic diversity is distributed geographically and among isolates using different hosts has never been examined with DNA sequence data. Here we describe the global phylogeography of S. mansoni using more than 2500 bp of mitochondrial DNA (mtDNA) from 143 parasites collected in 53 geographically widespread localities. Considerable within-species mtDNA diversity was found, with 85 unique haplotypes grouping into five distinct lineages. Geographical separation, and not host use, appears to be the most important factor in the diversification of the parasite. East African specimens showed a remarkable amount of variation, comprising three clades and basal members of a fourth, strongly suggesting an East African origin for the parasite 0.30-0.43 million years ago, a time frame that follows the arrival of its snail host. Less but still substantial variation was found in the rest of Africa. A recent colonization of the New World is supported by finding only seven closely related New World haplotypes which have West African affinities. All Brazilian isolates have nearly identical mtDNA haplotypes, suggesting a founder effect from the establishment and spread of the parasite in this large country.

A potential vector of Schistosoma mansoni in Uruguay

Susceptibily experiments were carried out with a Biomphalaria straminea-like planorbid snail (Biomphalaria aff. straminea, species inquirenda) from Expinillar, near Salto (Uruguay), in the area of the Salto Grande reservoir, exposed individually to 5 miracidia of Schistosoma mansoni (SJ2 and BH2 strains). Of 130 snails exposed to the SJ2 strain, originally infective to Biomphalaria tenagophila, 30 became infected (23%). The prepatent (precercaria) period ranged from 35 to 65 days. The cercarial output was irregular, following no definite pattern, varying from 138 to 76,075 per snail (daily average4.3 to 447.5 and ending up with death. Three specimens that died, without having shed cercarie, on days 69 (2) and 80 after exposure to miracidia, had developing secondary sporocysts in their tissues, justifying the prospect of a longer precercarial period in these cases. In a control group of 120 B. teangophila, exposed to the SJ2 strain, 40 became infected, showing an infection rate (33.3%) not significantly different from that of the Espinillar snail (X**2 = 3.26). No cercarie were produced by any ofd the espinilar snails exposed to miracidia of the BH2 strain, originally infective to Biomphalaria glabrata. Four specimens showed each a primary sporocyst in one entecle, which disappeared between 15 and 25 days post-exposure, and two others died with immature, very slender sporocysts in their tissues on days 36 and 54. In a control group of 100 B. glabrata exposed to BH2 miracidia, 94 shed cercariae (94%) and 6 remained negative. Calculation of Frandsen's (1979a, b) TCP/100 index shows that "Espinillar Biomphalaria-SJ2 S. mansoni" is a vector-parasite "compatible" combination. Seeing that tenagophila-borne schistosomiasis is prevalent in Rio de Janeiro and Säo Paulo states and has recently spread sothwards to Santa Catarina state, and the range of B. tenagophila overlaps taht of the Espinillar Biomphalaria, the possibility of schistosomiais establishing itself in Uruguay, although not imminent, is not to be disregarded

Self-fertilization in the freshwater snails Helisoma duryi and Helisoma trivolvis

Autofecundaçäo nos moluscos planorbídeos helisoma duryi e Helisoma trivolvis - Cinquenta espéciems de cinco cepas (10 de cada cepa) de helisoma duryi de Lima (Peru), St. Croix (Ilhas Virgens), Formosa (Brasil), Cartago (Costa Rica) e St. Vicent (Pequenas Antilhas), criados isoladamente durante cerca de 150 dias, depositaram 103 ovos.Os números de ovos postos pelos 10 espécimes de cada cepa foram respectivamente (ovos viáveis entre parênteses): 44(26), 1(1), 5(0), 15(7) e 38(0). A produçäo de ovos variou amplamente entre os indivíduos de cada cepa, havendo em todas elas, exceto na de St. Vicent, certo número de espécimes (3 a 9) que näo puseram nenhum ovo. Depois do período de observaçäo os espécimes isolados, inclusive os que näo puseram ovos, prontamente passaram a copular quando acasalados e produziram grande número de ovos. Os F1s gerados por autofecundaçäo foram perfeitamente interférteis, produzindo decendência normal por fecundaçäo cruzada. Dez espécimes de Helisoma trivolvis (cepa de Zempoala, México), também criados isoladamente durante cerca de 120, depositaram 646 ovos, dos quais 74 foram inviáveis. Nossos dados, somados aos de poucos estudados anteriores citados no texto, mostraram que no H. duryi a autofecundaçäo näo é um modo alternativo de reproduçäo täo eficiente quanto em muitos outros planorbídeos (no H. trivolvis é um pouco mais eficiente que no H. duryi). H. duryi, portanto, beneficia-se muito menos do hermafroditismo funcional que, além de outras vantagens, capacita um único indivíduo virgem a fundar uma nova populaçäo

Further experiments on susceptibility of Biomphalaria amazonica to Schistosoma mansoni

Uma amostra de Biomphalaria amazonica de Porto Velho, Estado de Rondônia, foi exposta a miracídios de Schistosoma mansoni (cepa SJ2) de Säo José dos Campos, Estado de Säo Paulo (cinco miracídios para cada molusco). Foi utilizada água recém-colhida do criadouro dos moluscos para verificar se sua qualidade era compatível com a eclosäo dos miracídios e a penetraçäo destes nos caramujos. O índice de infecçäo resultante foi de 3,5%, em comparaçäo com 45% nos controles (B. tenagophila). Em relaçäo à cepa de B. tenagophila, mostrou a B. amazonica, além de menor índice de infecçäo, um período prepatente mais longo e menor produçäo de cercárias. Estas características parecem indicar que a B. amazonica é má hospedeira do S. mansoni, como a B. straminea, mas deve-se levar em conta que, apesar disso, esta última é reconhecidamente boa vetora do parasito em áreas hiperendêmicas do nordeste do Brasil. Estes resultados indicam a possibilidade de introduçäo da xistosomose mansoni na Amazônia Ocidental, onde é comum a ocorrência da B. amazonica