Natural infection of Lymnaea glabra and Lymnaea truncatula by Fasciola hepatica and/or Paramphistomum daubneyi was studied at two periods of risk (June-July and September-October) in 11 French farms known for their high prevalences of F. hepatica infection in ruminants. A total of 1,778 L. truncatula and 2,396 L. glabra measuring 6 mm or more in height were collected to determine the prevalence of natural infection with F. hepatica and P. daubneyi. The role of four factors, i.e. season, snail co-infection (F. hepatica-P. daubneyi), ruminant host and the existence of single or mixed intermediate host communities, was investigated. There were no differences in prevalences between the two risk periods. Co-infections in L. glabra were more frequent than expected. The prevalences of infection with F. hepatica or P. daubneyi in L. glabra were higher in farms rearing sheep than in farms rearing cattle. A similar finding was also noted for L. truncatula infected with P. daubneyi only. L. glabra was a much better intermediate host for F. hepatica and P. daubneyi when it was the only available snail, possibly indicating an adaptation of parasites to their less usual host in local conditions. The two trematodes preferably developed in L. truncatula rather than in L. glabra when both host species lived in the same places.

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Changes in gastro-intestinal helminth species diversity in lambs under mixed grazing on irrigated pastures in the tropics (French West Indies).

The development of gastro-intestinal helminth diversity was monitored in lambs grazing alone or grazing with heifers in the ratio one heifer to four lambs. Five successive cohorts of lambs were studied from January 1994 to May 1996. Each cohort of lambs grazed irrigated pastures of Pangola grass for 4 months (from weaning to 6 months of age). A total of 50 lambs was necropsied and their worms counted and identified at the end of each grazing period. Four heifers were also necropsied on one occasion. Special attention was dedicated to the identification of the most pathogenic worm, i.e. Haemonchus spp. Malate dehydrogenase polymorphism in H. contortus was studied in order to evaluate changes between cohorts and between grazing managements. The species diversity was estimated by Shannon diversity indices (main species or all species). It was higher in the mixed grazing group than in the lambs that grazed alone. Diversity increased in successive cohorts. This was due in part to the acquisition of Cooperia spp. of cattle origin. The increase in diversity in the mixed grazing lambs corresponded to the lower faecal egg excretion and better weight gains recorded previously in that group. There seemed to be no cross-transmission of H. similis found in heifers and H. contortus harboured by lambs. The latter species was not morphologically or genetically different in the lambs grazed alone or with heifers, indicating that the presence of cattle did not modify qualitatively the transmission of H. contortus.

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[Receptivity of some Helicids frequent in Morocco to the infestation by the larvae of Protostongylids. Factors of variation (author's transl)].

Several species of Helicids common on pasture in the Rabat area were infected by a plurispecific mixture of larvae of Protostrongylids. The fecal or pulmonary origin of the larvae does not seem to influence their infective ability. The age of the larvae used for infection displays an important role on the future degree of infection of Molluscs: the young larvae are more infestive. The Helicids that were most receptive to infection are, arranged in a decreasing order: Otala lactea, Cochlicella conoidea, C. acuta and Euparypha pisana, Helicella gigaxii. O. lactea and E. pisana permitted the development of Muellerius capillaris, Cystocaulus nigrescens and Neostrongylus linearis. The former species of Helicid is a new intermediary host. The two species of Cochlicella were not suitable for M. capillaris. The Helicids ensure the quantiative and specific regulation of the infection of the Ovines.

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[Experimental infestation of Cochlicella ventricosa with L1 larvae of protostrongylids (author's transl)].

Young land-snails (Cochlicella ventricosa) were infested with a plurigeneric mixture of first-stage larvae of Protostrogylids. Cochlicella ventricosa is good host for Cystocaulus and Neostrongylus. Only one larva is able to ensure its complete evolution at a first infestation. A second larva follows the same process, at a second infestation. Such a regulation of the infestation recalls the limitation phenomenon. Hypothesis concerning this regulation process are discussed.20

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[Comparative strategy of natural infestation by Teladorsagia circumcincta and T. trifurcata in sheep].

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Animals↗

PubMedDate not supplied

[Motility and infestivity of first-stage Protostrongylid larvae. Factors of variation (author's transl)].

The infection of land-snails was realised in order to relate the motility of Protostrongylid first-stage larvae to their infectivity. Various factors such as the age of larvae, their density, the composition of the conservation liquid and the temperature were tried on the motility of larvae. A clear relation appeared between motility and infestivity of larvae. The age, density of larvae, and cold did influence negatively their motility. On the contrary increases in temperature and optimal concentrations of magnesium, calcium and sodium salts did influence positively the motility. Induced variations of motility did provoke related fluctuations of infestivity.

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Nematode genera diversity in cattle: similarity of between-sire progenies.

Breeding cattle for resistance to nematode infection is mostly based on egg excretion. This, however, does not allow for generic identification of the nematodes involved. Unless we know whether the selected resistance is directed against one or several particular genera, a strong bias could be introduced in the selection programs. In order to estimate the likelihood of this potential bias we investigated nematode genera diversity in the progeny of four sires in 1992 and seven sires in 1994. Three of the four Aberdeen Angus sires used in 1992 were related while the seven sires in 1994 were unrelated. Diversity was assessed using at least ten individual faecal cultures for each progeny group during each of the two sampling periods (beginning and end of grazing period, April and September). It was estimated by the relative proportion of each genera (Ostertagia, Cooperia, Haemonchus, Trichostrongylus and Oesophagostomum) or by either the Shannon (genera diversity) or Pielou (genera evenness) index. The Shannon index was repeatable when measured at 2-week intervals within the same progeny group on ten random faecal samples. No significant difference was recorded between sire genera diversity over the two sampling periods. This indicated that hosts have a limited effect on the nematode genera diversity as assessed by faecal cultures, and that the selection of resistant hosts could probably be achieved using faecal egg counts.

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