Daniel Rondelaud

Oviposition of Lymnaea truncatula infected by Fasciola hepatica under experimental conditions

Abstract Experimental infections of Lymnaea truncatula by Fasciola hepatica (one, two, or three miracidia per snail) were carried out under laboratory conditions to analyze the oviposition of infected snails and determine the characteristics of their egg masses. In the infected snails from the three groups, egg-laying steadily decreased until week 4 postexposure and stopped afterward until the end of the experiment, except for the cercaria-shedding snails from the one-miracidium group, for which low numbers of egg masses were noted between weeks 9 and 12. In uninfected snails the number of egg masses decreased until week 4 and remained low during subsequent weeks. At weeks 11 and 12 postexposure the natality rate was 98.9% in controls, 56% in the cercaria-shedding snails from the one-miracidium group, and 59.2–68.5% in uninfected snails. In the cercaria-shedding snails from the one-miracidium group the restoration of reproduction activity after week 8 may be explained by a lower parasite burden in these snails than in those from the two- and three-miracidium groups.

Fasciola hepatica: the infectivity of cattle-origin miracidia had increased over the past years in central France.

A retrospective study on experimental infections of Galba truncatula, originating from four populations, was carried out to determine the infectivity of Fasciola hepatica miracidia in snails either subjected to single-miracidium or bimiracidial exposures in 2006 and to compare it with results found before 1990 in other experiments using the same protocol. In single-miracidium infections, the prevalence of snail infection was significantly greater in 2006 than in experiments performed before 1980, while snail survival at day 30 postexposure showed insignificant differences. In bimiracidial infections, snail survival in two snail groups was significantly lower in 2006 than in experiments performed from 1981 to 1990, while insignificant differences were found for the other two populations of G. truncatula. Compared to results found between 1981 and 1990, the prevalence of snail infection did not significantly differ in 2006. In each population considered alone, the mean number of cercariae shed by infected snails did not significantly vary, whatever the date of experiment and the number of miracidia used for each exposure. The greater infectivity of F. hepatica miracidia towards snails might be the consequence of specific molecules such as triclabendazole used since 1990 to treat fasciolosis in cattle from central France.

Initial studies on infection ofLymnaea truncatula Müller byMuellerius capillaris müller andNeostrongylus linearis marotel (Nematoda, Protostrongylidae)

Protostrongylids have a two-host life cycle in which a mollusc serves as the intermediate host. A large number of snail species are susceptible to infection either as juveniles or as adults (Urban 1980; Cabaret 1984). However, only a few species of Lymnaea have been tested, including L. peregra (Urban 1980), L. stagnalis (Zdzitowiecki 1976), and L. truncatula (Soltys 1964). In all cases except the infection of L. peregra with Muellerius capillaris, the Lymnaea spp. were not suitable as intermediate hosts. The aim of the present study was to assess the susceptibility of L. truncatula to infection with two protostrongylid nematodes, M. capillaris and Neostrongylus linearis. Snails originated from a population living in a road ditch at Chezeau-Chrdtien near Mign6 (Indre) and were assumed to be free of natural infection with protostrongylid larvae since snails collected in this habitat had regularly proved to be negative on histological examination. The shells of animals were 1 or 4 mm high and formed part of the first annual generation. Snails were transported to the laboratory under isothermal conditions. Prior to infection, they were maintained for 48 h in standard breeding containers. First-stage larvae (L1) were extracted from faeces o} an experimentally infected goat (M. capillaris) or naturally infected sheep (N. linearis). Three groups each containing 75 snails with shells measuring I mm in height were formed: the first was used as a control; each of the other groups was exposed to either M. capillaris or N. linearis. Three other groups were similarly established using 4-ram-high snails. Snails were infected according to the method described by Cabaret and Dakkak (1979); each group was exposed to 100 L1 larvae for 4 h at 20 ~ After exposure, the snails were maintained in covered, closed-circuit aquaria for a maximum of 35 days using 10 individuals/din 3 water. The sediment, which was 10 cm thick, consisted of gravel lying under an oxygenated water sheet. The aquaria were kept at a constant

Consequences of invasion by Pseudosuccinea columella on the dynamics of native lymnaeids living on the acid soils of central France

ABSTRACT Eight road ditches located on granite and colonised by the native lymnaeids Galba truncatula or Omphiscola glabra were studied for 2 years to follow the distribution and density of these species in their habitats when the invasive lymnaeid Pseudosuccinea columella was introduced. Six other ditches populated only by a native lymnaeid or by P. columella were used as controls. The same experiment was also carried out for 3 years in seven water tanks placed in semi-natural conditions. The colonisation of P. columella was more rapid in habitats with G. truncatula than in those with O. glabra. Similarly, this colonisation led to a progressive decrease in the number of native lymnaeids in these ditches and this decrease was also faster for G. truncatula than for O. glabra. A similar decrease of G. truncatula and O. glabra was also noted when P. columella was introduced into water tanks placed in semi-natural conditions. The habitats of G. truncatula or O. glabra on the acid soils of central France can be successfully colonised by P. columella, and the establishment of this invasive species may lead to a decrease of the two native lymnaeids or even the local extinction of one of these (G. truncatula).