Anatomical studies of sibling species within neotropical lymnaeids, snail intermediate hosts of fascioliasis (original) (raw)
Related papers
Acta Tropica, 2002
The delimitation of cryptic species within the genus Lymnaea , which are the main vectors of fascioliasis, remains a topic of controversy. An analysis of genetic variability based on 12 enzyme loci revealed different fixed alleles at 9 loci between two sympatric samples of Lymnaea viatrix at the type locality in Lima, Peru. The absence of heterozygotes within this locality indicates the presence of isolated populations or cryptic species within L. viatrix . Significant genetic differences were also found between these two L. viatrix samples from Lima and other populations of L. viatrix in South America and in addition to species such as L. truncatula , L. cubensis and L. columella . Moreover, the lack of variability within each Lymnaea samples studied indicates the existence of a high selfing rate in each species. #
PLoS ONE, 2011
Background: Lymnaeid snails transmit medical and veterinary important trematodiases, mainly fascioliasis. Vector specificity of fasciolid parasites defines disease distribution and characteristics. Different lymnaeid species appear linked to different transmission and epidemiological patterns. Pronounced susceptibility differences to absolute resistance have been described among lymnaeid populations. When assessing disease characteristics in different endemic areas, unexpected results were obtained in studies on lymnaeid susceptibility to Fasciola. We undertook studies to understand this disease transmission heterogeneity. Methodology/Principal Findings: A ten-year study in Iran, Egypt, Spain, the Dominican Republic, Mexico, Venezuela, Ecuador and Peru, demonstrated that such heterogeneity is not due to susceptibility differences, but to a hitherto overlooked cryptic species, Lymnaea schirazensis, confused with the main vector Galba truncatula and/or other Galba/ Fossaria vectors. Nuclear rDNA and mtDNA sequences and phylogenetic reconstruction highlighted an old evolutionary divergence from other Galba/Fossaria species, and a low intraspecific variability suggesting a recent spread from one geographical source. Morphometry, anatomy and egg cluster analyses allowed for phenotypic differentiation. Selfing, egg laying, and habitat characteristics indicated a migration capacity by passive transport. Studies showed that it is not a vector species (n = 8572 field collected, 20 populations): snail finding and penetration by F. hepatica miracidium occur but never lead to cercarial production (n = 338 experimentally infected). Conclusions/Significance: This species has been distorting fasciolid specificity/susceptibility and fascioliasis geographical distribution data. Hence, a large body of literature on G. truncatula should be revised. Its existence has henceforth to be considered in research. Genetic data on livestock, archeology and history along the 10,000-year post-domestication period explain its wide spread from the Neolithic Fertile Crescent. It is an efficient biomarker for the follow-up of livestock movements, a crucial aspect in fascioliasis emergence. It offers an outstanding laboratory model for genetic studies on susceptibility/resistance in F. hepatica/lymnaeid interaction, a field of applied research with disease control perspectives.
Parasites & Vectors, 2014
Background: High prevalence of Fasciola hepatica infection (>70%) was noted during several outbreaks before the 2000s in several French farms where Galba truncatula is lacking. Other lymnaeids such as Lymnaea fuscus, L. glabra and/or Radix balthica are living in meadows around these farms but only juvenile snails can sustain complete larval development of F. hepatica while older snails were resistant. The low prevalence of infection (<20%) and limited cercarial production (<50 cercariae per infected snail) noted with these juveniles could not explain the high values noted in these cattle herds. As paramphistomosis due to Calicophoron daubneyi was not still noted in these farms, the existence of another mode of infection was hypothesized. Experimental infection of several successive generations of L. glabra, originating from eggs laid by their parents already infected with this parasite resulted in a progressive increase in prevalence of snail infection and the number of shed cercariae. The aim of this paper was to determine if this mode of snail infection was specific to L. glabra, or it might occur in other lymnaeid species such as L. fuscus and R. balthica. Methods: Five successive generations of L. fuscus and R. balthica were subjected to individual bimiracidial infections in the laboratory. Resulting rediae and cercariae in the first four generations were counted after snail dissection at day 50 p.e. (20°C), while the dynamics of cercarial shedding was followed in the F5 generation. Results: In the first experiment, prevalence and intensity of F. hepatica infection in snails progressively increased from the F1 (R. balthica) or F2 (L. fuscus) generation. In the second experiment, the prevalence of F. hepatica infection and the number of shed cercariae were significantly lower in L. fuscus and R. balthica (without significant differences between both lymnaeids) than in G. truncatula. Conclusion: The F. hepatica infection of several successive snail generations, coming from parents infected with this parasite, resulted in a progressive increase in prevalence and intensity of snail infection. This may explain high prevalence of fasciolosis noted in several cattle-breeding farms when the common snail host of this digenean, G. truncatula, is lacking.
Morphological studies of Lymnaeidae snails from human fascioliasis endemic zone of Bolivia
The taxonomic position of the Lymnaeidae from the Bolivian Altiplano has been unclear. On the basis of conchological characters, some authors reported two species from this area, Lymnaea viatrix and L. cubensis while others, considering also anatomical characters, considered L. viatrix as a synonym of L. cubensis. More recent studies demonstrated genetic identity between the Bolivian lymnaeids and L. truncatula from the Iberian Peninsula. Populations recognized as L. cubensis correspond to a distinct genetic group, but genetic information was not available for L. viatrix. In the light of these genetic results, a morphometric study of both the shell (using Raupian parameters) and male reproductive system was carried out of L. cubensis from Cuba (type locality), Dominican Republic, Guadeloupe and Venezuela, and of L. truncatula from Bolivia, France, Portugal, Spain and Morocco. Syntypes of L. viatrix from Argentina (var. A. ventricosa) and specimens of L. viatrix (var. B. elongata) from the type locality, Peru, were also studied (conchological characters only). The conchological study showed the presence of a large amount of variability between populations. This variability was not congruent with genetic results. A large amount of variability was also found using anatomical characters of the male reproductive system and all of them clearly separate L. cubensis from L. truncatula independently from geographical origin. Thus anatomical characters, unlike conchological parameters, do differentiate taxonomic species inferred from genetic studies.
Morphological studies of lymnaeid snails from the human fascioliasis endemic zone of Bolivia
2000
The taxonomic position of the Lymnaeidae from the Bolivian Altiplano has been unclear. On the basis of conchological characters, some authors reported two species from this area, Lymnaea viatrix and L. cubensis while others, considering also anatomical characters, considered L. viatrix as a synonym of L. cubensis. More recent studies demonstrated genetic identity between the Bolivian lymnaeids and L. truncatula from the Iberian Peninsula. Populations recognized as L. cubensis correspond to a distinct genetic group, but genetic information was not available for L. viatrix. In the light of these genetic results, a morphometric study of both the shell (using Raupian parameters) and male reproductive system was carried out of L. cubensis from Cuba (type locality), Dominican Republic, Guadeloupe and Venezuela, and of L. truncatula from Bolivia, France, Portugal, Spain and Morocco. Syntypes of L. viatrix from Argentina (var. A. ventricosa) and specimens of L. viatrix (var. B. elongata) from the type locality, Peru, were also studied (conchological characters only). The conchological study showed the presence of a large amount of variability between populations. This variability was not congruent with genetic results. A large amount of variability was also found using anatomical characters of the male reproductive system and all of them clearly separate L. cubensis from L. truncatula independently from geographical origin. Thus anatomical characters, unlike conchological parameters, do differentiate taxonomic species inferred from genetic studies.