DIFFERENTIAL SUITABILITY OF SIX SPECIES OF LYMNAEID SNAILS EXPOSED TO FASCIOLA HEPATICA LINNAEUS, 1758

The competence of lymnaeids as intermediate hosts of Fasciola hepatica has not been studied in southern Louisiana and furthermore the taxonomic status of these snails is still controversial among malacologists. There are different opinions as to whether Fossaria (Bakerilymnaea) cubensis or Lymnaea (Pseudosuccinea) columella acts as the main intermediate host in enzootic areas of Louisiana. In the present study, the suitability of those two snails as hosts for F. hepatica from a single source in Louisiana was compared with four other species of lymnaeids from different geographic areas and the study was undertaken with evaluation of "vector competence". Groups of young snails were exposed to three different densities of miracidia, 1,5, and 10, in 0.7ml of spring water in a Beem('(REGTM)) capsule during 3 hrs at room temperature. They were checked for infection at day 14 postexposure; then they were dissected or fixed at different times. Percentages, locations of intramolluscan stages and intensity of infection were recorded, as well as the variations in length of the incubation period. Histopathological studies were also done. The results show that L. (P.) columella from Louisiana is a more suitable host (48.6% became infected) than F. (B.) cubensis (19.2% became infected). The percentages of the positive controls becoming infected were: 68.9% for L. (P.) columella from Michigan, and 32.2% for L. gedrosiana from Iran. The study of histological sections did not show any significant differences in the pathological manifestations in the infected snails. The negative controls were: L. natalensis from Senegal, Stagnicola elodes from Michigan, and Stagnicola attenuata from Hidalgo, Mexico, an enzootic area of fascioliasis. The latter species was studied for the first time and its internal anatomy was compared with S. elodes. Although the results show that F. (B.) cubensis and L. (P.) columella have some degree of competence as intermediate hosts of F. hepatica under laboratory conditions, field observations on the habitat of these snails in southern Louisiana and the characteristic management of cattle, indicate that the former snail is more important as an intermediate host in this enzootic area than is the latter.