Characterization ofFasciola hepaticaredial generations by morphometry and chaetotaxy under experimental conditions

Abstract

Morphometric and chaetotactic studies were carried out on the body and cephalic regions of the rediae of Fasciola hepatica (Trematoda: Fasciolidae) in order to precisely identify the different redial generations of this trematode in Lymnaea truncatula under experimental infection. At day 49 post-exposure at 20°C, the length of the redia was significantly higher in the first group of the first generation (R1a) compared with successive generations, R1b, R2a and R2b/R3a. The width of the body was similar in the R1a, R1b, and R2a rediae, but was significantly lower in the R2b/R3a groups. The intrapharyngeal cavity of R1a rediae was significantly wider compared with the R1b, R2a, and R2b/R3a groups, whereas the pharyngeal wall was significantly thicker in the R2b/R3a rediae compared with the R1b and R2a groups. Four other measurements, namely the maximum length and width of the pharynx, diameter of the mouth, and width of intestine, also showed significant variations in relation to pharyngeal morphology and age of infection. Discriminant analysis based on these measurements demonstrated that 98% of the rediae were readily categorized into the four groups identified. The number of perioral sensillae ranged from 126 to 160 but a significant difference was only noted between the mean values of the first generation and those of the group R2b/R3a. From these parameters, the maximum width of the pharyngeal lumen was found to be the best characteristic in the identification of the redial generations.

Fasciola hepatica : the effect of food quality on the development of redial generations in Galba truncatula infected with allopatric miracidia

“…Indeed, the developmental pattern of redial generations was dependent on the behaviour of the R1a redia after its exit from the sporocyst. If this R1a redia remained alive throughout snail infection, the usual development of redial generations occurred (Augot et al 1998). In contrast, if this mother redia died during week 2 or week 3 of snail infection, the development of generations was unusual and resulted in a lower redial burden (Augot et al 1999).…”

Fasciola hepatica and Paramphistomum daubneyi: changes in prevalences of natural infections in cattle and in Lymnaea truncatula from central France over the past 12 years

“…The most differentiated larval forms of F. hepatica and/or P. daubneyi found in most infected snails were cercaria-containing rediae and free cercariae; in the other snails, immature rediae were noted. Cercariaecontaining rediae of F. hepatica possess a well-developed pharynx, collar rings and pairs of appendages in the third posterior part of their bodies [5]. In contrast, the rediae of P. daubneyi are shorter with a small pharynx, and their bodies lacked a collar and appendages [2].…”

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).…”

“…In the case of F. hepatica, morphometric studies on the body and cephalic region of rediae were carried out by Augot et al (1998Augot et al ( , 1999 to identify their different generations. However, the values given for the rediae of both Fasciola in the previous reports are difficult to compare, as each study was performed under different experimental conditions (temperature, miracidial dose, or shell height of snails at exposure, for example).…”