Susceptibility and compatibility experiments were carried out with 700 Biomphalaria tenagophila from the Paraná River basin exposed to infection with Schistosoma mansoni. Individual infection was performed with 10 miracidia of SJ2 strain from the Paraiba valley (Brazil) originally infective to B. tenagophila. These snails were laboratory-breed progeny of B. tenagophila collected from six localities of Argentina and one from Paraguay. From Argentina: Rincón de Vences (7%) and Posadas (11%) became infected with S. mansoni and the calculation of Frandsen's index (TCP/100) shows that they were Class II poorly compatible. Those snails from Goya (22%), Maloyas (5%), and Berón de Astrada (3%) were Class III compatible to the S. mansoni. None of the 100 snails exposed from Caá-Catí became infected (Class 0 incompatible). Tested samples from Paraguay (Encarnación) were infected (20%) and compatible (Class III). It was also studied the persistence of the infection in 244 snails of the first generation (F1) of those that were susceptible from three places. It was demonstrated an increment of the susceptibility in the F1 from Maloyas (chi2 = 27.22; p = 0.0001) and Posadas (chi2 = 4.24; p = 0.04). The results point out the possibility that schistosomiasis might be able to spread into the Paraná River basin where B. tenagophila exists.

Corrientes province is located in the humid subtropical region of Argentina northeast on the left riverbank of Paraná River in the border with the South of Brazil. This is a region without schistosomiasis but planorbid and rodents that would serve as host of the life cycle of Schistosoma mansoni inhabit here. The objective of this work is to know the role of rodent as definitive host of schistosomiasis. Biomphalaria tenagophila (4 to 8 mm Ø) from Maloyas, exposed each to 10 miracidia of SJ2 strain of S. mansoni natives from Brazil were susceptible (5%). The degree of compatibility was Class II of Frandsen. Five wild rodents captured in the same ecological niche were exposed transcutaneously to infection with 40 cercariae for animal: two Olygoryzomys flavescens, two Holochilus braziliensis, and one Scapteromys tuncidus. Only one H. braziliensis eliminated eggs in feces. Prepatent period was of 83 days. With these feces, two of six (33.3%) B. tenagophila from Maloyas were infected with miracidium. It was demonstrated, in an area free of schistosomiasis, that life cycle S. mansoni is closed with planorbid and rodents that live in the same ecological niche.

To study the possibility that schistosomiasis might be able to spread into the basins of the Paraná and Uruguay rivers, 1 711 snails were experimentally exposed to infection with Schistosoma mansoni. These snails were laboratory-bred progeny of Biomphalaria tenagophila collected from 15 populations in the geographic area under consideration. Three strains of S. mansoni were used: BH2, adapted to B. glabrata, and SJ and SJ2, adapted to B. tenagophila. None of the 543 snails exposed to the BH2 strain became infected, nor did any of the 668 exposed to SJ. However, of the 500 exposed the SJ2, 4 of 163 snails (2%) from Ayolas, a locality in the Paraná basin, were susceptible, as were 8 of 45 (18%) from Fuente Salto, in the Uruguay basin. These findings are similar to those of studies done in other geographic areas, where some populations of B. tenagophila do not become infected with S. mansoni while others are susceptible. The results of this study signal the possibility of the expansion of schistosomiasis into a broad region of South America in which B. tenagophila is found.

Con el fin de estudiar la posibilidad de extensión de la esquistosomiasis a las cuencas de los ríos Paraná y Uruguay se expusieron experimentalmente a infección por Schistosoma mansoni 1 711 caracoles criados en laboratorio a partir de ejemplares de Biomphalaria tenagophila recolectados en 15 poblaciones de dicha zona geográfica. Se utilizaron tres cepas de S. mansoni: la BH2, adaptada a B. glabrata, y las cepas SJ y SJ2, adaptadas a B. tenagophila. No se produjo infección de ninguno de los 543 caracoles expuestos a la cepa BH2 ni de los 668 expuestos a la SJ. En cambio, de los 500 expuestos a la cepa SJ2, fueron susceptibles a la infestación 4 de 163 caracoles (2%) procedentes de Ayolas, una localidad de la cuenca del Paraná, y 8 de 45 (18%) de los procedentes de Fuente Salto, en la cuenca del Uruguay. Estos hallazgos son similares a los de otras áreas geográficas en las que se han encontrado poblaciones de B. tenagophila que no se infectan y otras que sí son susceptibles a S. mansoni. Los resultados de este trabajo señalan la posibilidad de expansión de la esquistosomiasis a una amplia región de Sudamérica en la que se halla B. tenagophila.