Fasciola hepatica and Fasciola gigantica: comparative morphometric studies on the redial stage of both species.

Experimental infections of Galba truncatula with Fasciola gigantica or F. hepatica were carried out under laboratory conditions (20 degrees C) to determine the characteristics of rediae of both species via their morphometry and to find reliable measurements that might be efficiently used to discriminate between the rediae of both species of Fasciola. These results were compared to those of another snail: Radix natalensis, infected with either F. gigantica or F. hepatica under the same protocol. At day 28 post-exposure, abortive infections with F. hepatica were found in a group of R. natalensis. By contrast, live rediae were observed in the other three groups. The group of infected snails and the redial category significantly influenced the mean values of the seven measurements studied and those of three indices. Using the PSLD Fisher test, it was found that the index, distance from the anterior end of the body to the collar/length of the body, was an efficient means of distinguishing the rediae of F. hepatica from those of F. gigantica [second-appearing mother rediae (R1b) of the first generation, 0.14 instead of 0.22; daughter rediae (R2a) produced by the first mother rediae, 0.19 instead of 0.24]. Another index, distance from the anterior end of the body to the collar/diameter of the collar, could also be used to discriminate between rediae (R1b, 0.80 for F. hepatica instead of 1.09 for F. gigantica; R2a, 0.90 instead of 1.26, respectively). Compared to measurements recorded for the rediae of F. hepatica, rediae of F. gigantica can be characterized by the following measurements: the diameter of the pharyngeal lumen and the distance from the anterior end of the body to the collar for larvae developed in R. natalensis, and the length of the body and the distance from the posterior end of the body to lateral projections for those found in G. truncatula. The species of snail host and, consequently, its growth, as well as the species of Fasciola, had a significant influence on the morphometric characters of the redial stage.