Development Of Redial Generations Research Articles

Fasciola hepatica: the redial generations in juvenile Pseudosuccinea columella.

Juvenile Pseudosuccinea columella, measuring 1 or 2mm in height, were subjected to single-miracidium infections with Fasciola hepatica to determine the developmental pattern of redial generations and count free and live rediae according to their generation. Controls were constituted of juvenile Galba truncatula infected according to the same protocol. In the four groups, redial counts were performed in snails dissected every week from day 7 to day 49 post-exposure at 20°C. Most infected snails showed a normal development of redial generations, whatever the lymnaeid species. In P. columella, the total number of live rediae on day 49 was 24.6 and 34.6 per infected snail in the 1 and 2-mm groups, respectively (instead of 11.5 and 18.8 rediae in the corresponding groups of G. truncatula). A single mother redia (R1a) producing only daughter rediae of the second generation was noted in each snail of three groups, while the 2-mm P. columella showed the presence of a single (43 snails/71) or two (28/71) R1a redia(e) within their bodies. The mean number of other mother rediae and that of daughter rediae of the second generation were low in the 1 and 2-mm groups of both lymnaeids. Besides, there was a delay in redial development. The development of two live R1a rediae in several P. columella from the 2-mm group needs to verify if this process would be specific to P. columella or would occur in other lymnaeid species known for their good susceptibility to the digenean and their larger size to allow harbouring rediae.

Fasciola hepatica: development of redial generations in experimental infections of Pseudosuccinea columella

Experimental infections of Egyptian Pseudosuccinea columella with one or two miracidia of Fasciola hepatica per snail were carried out to determine the developmental pattern (normal or abnormal) of redial generations and specify the number of free rediae developing in snails according to their generation. Controls were constituted by a French population of Galba truncatula infected according to the same protocol. Most infected P. columella showed a normal development of redial generations (96.2-98.1 vs 75.5-85.7% for G. truncatula). In each redial category, free rediae were more numerous in P. columella than in G. truncatula, and their number were also greater in the two-miracidia groups than in single-miracidium infections for each lymnaeid considered separately. This increase in redial production was mainly due to the number of first mother (R1a) rediae producing daughter rediae only: 2 per P. columella (vs one redia in G. truncatula) in single-miracidium groups and 3.1 (vs 1.9) in the two-miracidia groups. In P. columella, the mean total number of free rediae developing in single-miracidium and bimiracidial infections was 77.2 and 117.6, respectively (instead of 33.5 and 52.1 rediae in G. truncatula). The number of F. hepatica rediae present in P. columella was related to the number of fully grown sporocysts and the quantity of R1a rediae which developed into the snail body.

Fasciola hepatica: the developmental patterns of redial generations in naturally infected Galba truncatula.

A retrospective study on 1,211 snails naturally infected with Fasciola hepatica in central France was carried out to determine the numbers of full-grown sporocysts from which infections derived, to specify the developmental patterns of redial generations (normal or abnormal) and to count live and free rediae. In the department of Haute Vienne (siliceous subsoils), most snails showed single-sporocyst infections, with normal (46.3%) or abnormal (33.9%) development of redial generations. Two-sporocyst infections were scarcer (a total of 10.6%), while snail co-infections with F. hepatica and Paramphistomum daubneyi (8.0%) were found since 1996. In the department of Indre (calcareous subsoils), single-sporocyst infections showing normal development of rediae were the most numerous (58.0%), while the frequency of single-sporocyst infections with abnormal development was strongly decreased (4.3%). Two-sporocyst infections (with normal development of generations) and co-infections with F. hepatica and P. daubneyi slightly increased in frequency. The redial burdens found in snails collected from the department of Indre were significantly higher than those noted in snails originating from the department of Haute Vienne, whatever the type of snail infection; and these increases in numbers especially concerned the rediae of the second and subsequent generations. The results might be explained by the lower calcium ion content (7-23 mg/l) present in waters from the department of Haute Vienne which would induce a slower growth of infected snails (the shell height of adults scarcely reached 8 mm) and, consequently, would create barely favourable conditions for the development of the first rediae of the first generation within snails. However, the quality of the diet provided as food for snails and its influence on the development of redial generations cannot be excluded.

Fasciola hepatica: the infection rate and the development of redial generations in Lymnaea truncatula exposed to miracidia after experimental desiccation and activation in water.

Adult Lymnaea truncatula were subjected to 10 days of experimental desiccation and then remained in water for 1 or 8 days before each was exposed to a single miracidium. The infection rate was lower in these snails than in infected controls that were not exposed to stress (52-54% vs 73%). The redial burden clearly decreased in stressed snails (18-25 rediae per snail) than in controls (43 rediae). This numerical decrease concerned essentially: i) live independent rediae of the first generation and the first cohort of the second generation, and ii) dependent rediae of subsequent generations. Mature rediae were more numerous in the first cohort of the second generation than in the other generations. Desiccation before exposure limited the size of the redial burden but placement in water for 8 days just after the stress attenuated the effects of this factor.