Fascioliasis humana y animal en sudaméricacaracterización molecular de los lymnaeidos vectores y sus implicaciones en transmisión y epidemiología

Resumen

Fascioliasis is a parasitic disease of humans and livestock caused by fluke species of the genus Fasciola. In South America, this disease is caused by Fasciola hepatica and gives rise to a serious public health problem, including many human endemic areas where children and females are the most affected and animal endemic areas almost throughout. This disease is transmitted by specific freshwater snails of the family Lymnaeidae, within a frame of transmission and epidemiology pronouncedly influenced by climate factors and environmental conditions. The present work includes the genetic characterisation of the Iymnaeid species found in selected endemic areas of nine countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, Brazil, Uruguay and Argentina. Molecular markers used were the 18S gene, the ITS-2 and the ITS-1 spacers of the nuclear ribosomal DNA and the 16S ribosomal gene and the codifying cox1 gene of the mitochondrial DNA. Molecular results show that there are nine valid species: Lymnaea cubensis, L. cousini, L. meridensis, L. schirazensis, L. viator, L. neotropica, Galba truncatula, Pectinidens diaphana and Pseudosuccinea columella. This scenario pronouncedly differs from what was sustained by specialists so far. The phylogenetic analysis allows us to conclude that there are three well defined species groups, including a numerous one of seven species which may be ascribed to the conflictive Galba/Fossaria group plus two monospecific groups of the genera Pectinidens and Pseudosuccinea. The species Galba truncatula appears to be the main cause of human fascioliasis, independently of the transmission and epidemiology patterns, as this species is present in all human endemic areas studied in the aforementioned countries. The relationships of the Iymnaeids with the transmission and epidemiological patterns of the disease are analysed and a new pattern called "flatland at low altitude" is proposed. A study of mathematical modelling, remote sensing and geographic information system is applied to the "valley" fascioliasis pattern for the first time. The Wb-bs index proves to be more useful than the Mt index. The NDVI index gives rise to a statistically significant correlation between its results and fascioliasis prevalences, thus showing its usefulness. A new method is developed and applied to allow for the calculation of all the indices for each km2. The El Niño/La Niña-South Oscillation (ENSO) phenomenon proves to have a fascioliasis risk impact which is not uniform but depends on place and seasons. The difficulties in evaluating the climatic impact in cases of coexistence of two or more Iymnaeid vector species in an endemic area is highlighted.