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

Abstract

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.

Paramphistomum daubneyi: the number of sporocysts developing in experimentally and naturally infected Galba truncatula

“…Even if the high production of eggs by adult worms in the feces of ruminants allowed these multiple-miracidium infections, their occurrence in the snail would not be favorable for larval development of P. daubneyi, and this poses the question of their utility. Indeed, in the case of F. hepatica, which infected the same populations of snails, greater than two-sporocyst infections were scarce: only 0.7% in the case of snails collected from Haute Vienne and 2.7% in those from Indre (Rondelaud et al 2004). In the case of P. daubneyi, the most valid explanation was to interpret these multiple-miracidium infections as a consequence of an epizootic zoonosis, and further studies will be necessary to determine their outcome in snails over time.…”

“…As natural infections deriving from the development of one, two, or more sporocysts were found in the case of F. hepatica (Rondelaud et al 2004), this last finding poses the question of whether the redial burden noted in G. truncatula naturally infected with P. daubneyi would not originate from single-, bi-, or multiple-miracidium infections. To answer this question single-, bi-, or multiple-miracidium infections of G. truncatula with P. daubneyi were carried out in the lab to determine the number of fully grown sporocysts via the count of first-and second-generation rediae.…”

Natural prevalence in Cuban populations of the lymnaeid snail Galba cubensis infected with the liver fluke Fasciola hepatica: small values do matter

“…The variable number of rediae found inside each G. cubensis individual would depend on several factors, linked to the biology of parasite, of the host and the interaction between them. Mean numbers of rediae observed in naturally infected G. truncatula from France range between 15.8 and 25.7 when coming from one or two sporocysts, respectively (Rondelaud et al 2004a). In the current study, some individuals have attained more than 40 rediae with an observed maxima of 76 rediae.…”

Fasciola hepatica: an unusual case of adaptation to a Moroccan population of Galba truncatula

“…but without development, and by the important IDR production by all R1b rediae. Further studies are still necessary to determine the frequency of this new developmental pattern for redial generations by studying miracidial isolates of F. hepatica, originating from different countries, as it has never been found in naturally or experimentally infected snails from central France (Vignoles et al 2002;Rondelaud et al 2004a).…”

“…As the mother redia, which first emerges from the sporocyst (R1a redia), produces most of the second-generation daughter rediae, its life throughout snail infection or its early death influences the total burden of free rediae within the snail (31.7 rediae at day 49 post-exposure at 20°C if the R1a redia remains alive, instead of only 23.2 if this is not the case) (Rondelaud et al 2004a). By contrast, in less susceptible snails, larval development is slow, with a few rediae mainly belonging to the first generation, and cercarial production is low (Boray 1969;Vignoles et al 2002).…”