-A retrospective study was carried out over a 10-to 12-year period to analyse the changes in prevalences of natural fasciolosis and paramphistomosis among cattle and snails in central France, and to determine the causes which had induced these changes. The prevalences of natural fasciolosis in cattle increased from 1990 to 1993 (13.6% to 25.2%) and diminished afterwards up to 1999 (at 12.6%). Those of natural paramphistomosis showed a progressive increase between 1990 and 1999 (from 5.2 to 44.7%). The prevalences of natural infections and the numbers of free rediae counted in the snails (Lymnaea truncatula) infected with F. hepatica did not show any significant variations over time. By contrast, the prevalences of natural paramphistomosis in snails significantly increased from 1989 to 1996 and remained afterwards in the same range of values (3.7-5.3%), while the number of free rediae significantly increased up to 2000 (from a mean of 6.5 to 13.8 rediae per infected snail, respectively). Three hypotheses may explain the increase of paramphistomosis in cattle and snails: a better quality of diagnosis for the detection of P. daubneyi eggs in veterinary analysis laboratories, the use of specific molecules in the treatment of cattle fasciolosis since 1993, and the lack of an effective treatment up to now against cattle paramphistomosis. Since the objective of most farmers in central France is to obtain the highest antiparasitic efficiency with a single treatment of cattle per year, it is reasonable to assume that the prevalence of bovine paramphistomosis will continue to increase in the future. Résumé -Fasciola hepatica et Paramphistomum daubneyi : changements dans les prévalences des infestations naturelles chez les bovins et chez Lymnaea truncatula dans le centre de la France au cours des 12 dernières années. Une étude rétrospective a été réalisée sur une période de 10 à 12 années pour analyser les modifications qui se sont produites dans les prévalences de la fasciolose et de la paramphistomose naturelles chez les bovins et les limnées du centre de la France, et pour déterminer les causes qui ont provoqué ces changements. Chez les bovins, la prévalence de la fasciolose naturelle s'est accrue entre 1990 et 1993 (de 13,6 à 25,2 %) avant de diminuer par la suite jusqu'en 1999 (à 12,6 %). Celle de la paramphistomose naturelle a augmenté de manière progressive entre 1990 et 1999 (de 5,2 à 44,7 %). La prévalence de l'infestation naturelle avec F. hepatica et le nombre de rédies libres chez Lymnaea truncatula n'ont pas montré de variations significatives dans le temps. Par contre, la prévalence de l'infestation naturelle avec Paramphistomum daubneyi chez les limnées a présenté une augmentation significative entre 1989 et 1996 avant de rester ensuite dans la même gamme de valeurs (3,7-5,3 %), tandis que le nombre de rédies libres a augmenté jusqu'en 2000 (de 6,5 à 13,8 rédies en moyenne par mollusque infesté). Trois hypothèses peuvent expliquer cet accroissement de la paramphistomose chez les bovins et les mollus...
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.
Natural infections of three freshwater snails withFasciola hepaticaand/orParamphistomum daubneyiwere studied during two periods in 1996 and 1997 (June–July and September–October) on 18 farms located in the departments of Vienne and Haute Vienne (central France), and known for low prevalences ofF. hepaticainfections in ruminants. A total of 1573Lymnaea glabraand 1421L. truncatula6 mm high or more were collected in the meadows of 13 farms and dissected under laboratory conditions. Snails with single or concurrent infections ofF. hepaticaand/orP. daubneyiwere found for eachLymnaeaspecies. InL. truncatula, global prevalences of natural infections withF. hepatica(3.8% in June–July, and 3.6% in September–October) were significantly greater than those recorded forP. daubneyi(1.1% and 0.8%, respectively). InL. glabra, global prevalences ofF. hepaticainfections (0.4% in each investigation period) were significantly lower than those found inL. truncatula, whereas there were no significant differences between prevalences ofP. daubneyiinfections. A total of 2721Planorbis leucostomameasuring at least 4 mm in diameter were collected in the meadows of the other five farms on whichL. truncatulawas absent. In these planorbids, global prevalences of natural infections withF. hepaticawere 0.4% in each period of investigation. Contrary to fasciolosis, snail infections withP. daubneyiwere not noted on all farms of the Vienne and Haute-Vienne departments. Natural single or concurrent infections withF. hepaticaand/orP. daubneyiinL. glabraand a natural infection ofP. leucostomawithF. hepaticawere found in swampy meadows on acid soil.
Two experiments using seven populations of Galba truncatula were carried out to analyse the effect of food quality (cos lettuce only, or cos lettuce+Tetraphyll) on the characteristics of infections: (1) in a single population of G. truncatula infected by one of three digenea (first experiment), and (2) in seven populations of G. truncatula differing in their susceptibility to Fasciola hepatica miracidia (second experiment). In most groups, food quality did not have a significant effect on the survival of snails. The prevalence of infection in five populations was significantly higher in snails raised on lettuce+Tetraphyll (first and second experiments), whereas it was close to those noted in lettuce only-reared groups in the last two populations (second experiment). Despite the higher growth of cercariae-shedding snails when raised on the mixed diet, no significant differences were noted. Significant effects of parasite species (first experiment) and of snail population (second experiment) on the life-spans of cercariae-shedding snails were noted, whereas food quality did not influence this parameter. Except for a single snail population, cercarial production in groups raised on lettuce+Tetraphyll was significantly higher than that in groups on lettuce. The variability noted in the prevalence of snail infections and in the intensity of cercarial shedding might be explained by differences in the susceptibility of snail populations to F. hepatica infections, and/or by the fact that Tetraphyll would not have the same appetency for all populations of G. truncatula.
The development of redial burden and cercarial shedding were studied in two groups of Lymnaea truncatula subjected to successive cross-exposures to one miracidium of Paramphistomum daubneyi and one of Fasciola hepatica per snail, or vice versa. The results were compared with those obtained in controls subjected to two unimiracidial exposures to the same trematode species. The infection rate was 61% in the group cross-exposed to P. daubneyi/F. hepatica and 37% in that cross-exposed to F. hepatica/P. daubneyi; it was 37% in the control group exposed to F. hepatica and 21% in that exposed to P. doubneyi. Snails harboring larval forms of both trematodes were few in number in cross-exposed groups and the redial burden was low, with one trematode dominating over the other. Free cercariae of F. hepatica and those of P. daubneyi were significantly more numerous at day 35 in the group cross-exposed to P. daubneyi/F. hepatica than in the controls or the other cross-exposed group. Mixed cercarial sheddings were obtained from 40% of snails with emission in the group cross-exposed to P. daubneyi/F. hepatica and from 21% of those in the F. hepatica/P. daubneyi group. The numbers of P. daubneyi metacercariae were significantly greater in the group cross-exposed to P. daubneyi/F. hepatica than in the other cross-exposed group, whereas no significant difference in mean numbers was noted for the F. hepatica cysts. Repartition of metacercariae over the patent period was clearly more irregular for P. daubneyi than for the other trematode.
-Experimental infections of Lymnaea truncatula with a digenean species (Fasciola gigantica, F. hepatica, or Paramphistomum daubneyi) were performed under laboratory conditions to study the effect of four sources of food (microalgae, romaine lettuce, wheat germs, or modified Boray diet) on cercarial production. The mean number of F. hepatica, F. gigantica, or P. daubneyi cercariae was significantly greater when snail food was microalgae or Boray diet. The lowest cost prices for 100 metacercariae of F. hepatica (9.7-10.1 euros) were noted when algae of Boray diet were used as food for snails. In contrast, the highest prices (18.0-18.5 euros) were found in lettuce-reared snails. The choice of a source of food for breeding the intermediate hosts of F. hepatica and collecting metacercariae must take into account the importance of the commercial demand for metacercariae and will depend on the strategy the producer wishes to develop.breeding method / Fasciola hepatica / food / Lymnaea truncatula / Paramphistomum daubneyi Résumé -Influence de différentes sources de nourriture sur la production cercarienne chez des Lymnaea truncatula infestées expérimentalement par des Digènes. Des infestations expérimenta-les de Lymnaea truncatula avec un Digène (Fasciola gigantica, F. hepatica, or Paramphistomum daubneyi) ont été réalisées dans les conditions du laboratoire afin d'étudier l'impact de quatre types de nourriture (algues, laitue romaine, germes de blé, aliment modifié de Boray) sur la croissance des mollusques et la production cercarienne. La production cercarienne de F. hepatica, de F. gigantica ou de P. daubneyi était significativement plus élevée lorsque le mollusque était nourri avec des algues ou avec l'aliment modifié de Boray. Les prix de revient les plus faibles pour 100 métacercaires de F. hepatica (9,7-10,1 euros) ont été obtenus avec l'emploi d'algues ou de l'aliment modifié de Boray. Les 95 Vet. Res. 33 (2002) 95-100
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