Fascioliasis is widespread in livestock in Argentina. Among activities included in
a long-term initiative to ascertain which are the fascioliasis areas of most concern,
studies were performed in a recreational farm, including liver fluke infection in
different domestic animal species, classification of the lymnaeid vector and verification
of natural transmission of fascioliasis by identification of the intramolluscan trematode
larval stages found in naturally infected snails. The high prevalences in the domestic
animals appeared related to only one lymnaeid species present. Lymnaeid and trematode
classification was verified by means of nuclear ribosomal DNA and mitochondrial DNA
marker sequencing. Complete sequences of 18S rRNA gene and rDNA ITS-2 and ITS-1, and
a fragment of the mtDNA cox1 gene demonstrate that the Argentinian lymnaeid belongs
to the species Lymnaea neotropica. Redial larval stages found in a L. neotropica specimen
were ascribed to Fasciola hepatica after analysis of the complete ITS-1 sequence.
The finding of L. neotropica is the first of this lymnaeid species not only in Argentina
but also in Southern Cone countries. The total absence of nucleotide differences between
the sequences of specimens from Argentina and the specimens from the Peruvian type
locality at the levels of rDNA 18S, ITS-2 and ITS-1, and the only one mutation at
the mtDNA cox1 gene suggest a very recent spread. The ecological characteristics of
this lymnaeid, living in small, superficial water collections frequented by livestock,
suggest that it may be carried from one place to another by remaining in dried mud
stuck to the feet of transported animals. The presence of L. neotropica adds pronounced
complexity to the transmission and epidemiology of fascioliasis in Argentina, due
to the great difficulties in distinguishing, by traditional malacological methods,
between the three similar lymnaeid species of the controversial Galba/Fossaria group
present in this country: L. viatrix, Galba truncatula and L. neotropica. It also poses
a problem with regard to the use, for lymnaeid vector species discrimination, of several
molecular techniques which do not show sufficient accuracy, as those relying on the
18S rRNA gene or parts of it, because both L. neotropica and L. viatrix present identical
18S sequence.