Redial generations of Fasciola gigantica in the pulmonate snail Lymnaea truncatula

Abstract

Lymnaea truncatula, 4 mm in height, were subjected to infection by a single miracidium of Fasciola gigantica, then raised at 23°C until day 60 of the experiment. Histological study of these snails demonstrated a mean redial burden of 34 parasites at day 60, of which one third were degenerating forms. The mean number of living independent rediae did not exceed 5 for the first and second generations. Conversely, in subsequent generations there were as many as 18 rediae per snail at day 60. The first living redia of the first generation in particular gave rise to daughter rediae. Mature rediae appeared at day 35 and especially concerned the first and second generations at day 60. The authors conclude that development of the first and second redial generations occurs during the same period, and that the forms of the first cohort of the second generation are produced from the first redia of the first generation which originated from the sporocyst.

Fasciola gigantica: the growth and larval productivity of redial generations in the snail Lymnaea truncatula

“…in this experiment was lower than that noted by Dinnik and Dinnik (1956) in single-miracidium infections of Lymnaea natalensis (161 rediae/snail at day 47 p.e.) and by Rakotondravao et al (1992) in another French population of L. truncatula subjected to bimiracidial infections (24 rediae/snail). To explain this difference, the most valid hypothesis would be to admit that the Madagascan isolate of miracidia was not yet adapted to the French population of L. truncatula and that there was a certain degree of disparity between parasite and snail host.…”

“…The criteria utilized to recognize the redial generations and cohorts of F. gigantica were based on the combination of three important factors: the age of infection, the development of intraredial developmental stages (Dinnik and Dinnik 1956), and the general form of the pharynx (Rakotondravao et al 1992). The firstappearing mother redia from the sporocyst (R1a redia) has a large, spherical, thick-walled pharynx.…”

“…However, these results must be reconsidered, as each redial generation of F. gigantica was composed of two cohorts which each had a different development within the snail body (Rakotondravao et al 1992). In view of this, the two following questions arose: what is the growth of each redial cohort in the intermediate host; and, consequently, what is its larval productivity?…”

“…1). Using serial sections of L. truncatula infected with F. gigantica, Rakotondravao et al (1992) reported that three redial generations could be differentiated from each other by the shape of the pharynx and the intrapharyngeal lumen. A morphometric study of the redial pharynx (Augot et al 1995) demonstrated that the width of the lumen decreased from the first to the third generation and was therefore the more efficient parameter for identifying the redial generations of F. gigantica.…”

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

“…Because of the frequent movements of live rediae, the dimensions were only determined when the larvae were completely relaxed. Three categories of rediae for each species of Fasciola were considered in the present study according to the criteria used by Dinnik and Dinnik (1956), or by Rakotondravao et al (1992) to identify the rediae of F. gigantica, and by Augot et al (1998Augot et al ( , 1999 for those of F. hepatica. These categories are: (1) mother rediae appearing from the sporocyst first (R1a), (2) mother rediae appearing from the sporocyst second (R1b), and (3) daughter rediae from R1a (R2a).…”