Histopatología y relaciones Fasciola Hepatica- Lymnaea Truncatula y L. Palustris en infestación experimental

Abstract

After a revisión of histopathological features of «trematode / mo­llusc host» relationships and of methods of maintaining mollusc in laboratory conditions the author has studied the receptivity of local strains of Lympaea truncatula, L. palustris, L. stagnalis and L. auricu­laria strains to Fasciola hepatica: snails being maintained in the la­boratory on Oscillatoria spp. cultures. The first two species were ade­quate while the othors did not get invaded by miracidia.
The histopathological study, which light microscope, of  Fasciola hepatica/ Lymnae truncatula and L. palustris systems, makes evident that invasion by miracidia occurs before the elimination of its ciliary coating and that takes place through any soft area of the mollusc foot offering the greatest difficulties. In L. truncatula lesions are very mild and their quick healing is characterized by a cellular stratification after loss of cilia of the external coating of the mollusc. In L. palustris destruction is more severe and restoration more complex.
Sporocystes develop in situ. Those located in areas rich in fibrous tissue tend to degenerate being surrounded with a conjunctive capsule containing a great number of fibroblastes, amebocytes, and in L. pa­lustris, with polynuclear cells similar to foreing body cells in mammals. Those brought into the loose connective tissue appear surrounded by a clear area and they incline to continue their development.
After the 8th - 9th day some rediae are formed. These rediae migrate towards the cavity of the body, leaving some areas occupied by cellular detritus. Their presence in that cavity is well tolerated and their pathogenic effect when produced, seems to be simply due to com­pression. When they get into the hepatopancreas, they lodge in the inter­tubular tissue provoking a compression in the tubules and cellular de­mage consisting in the appearance of big vacuoles, rich in pigmentary substances and in a basophilic precipitate at the apical pole level. L. pa­lustris tubular epithelium presents a metaplasia in a stratified plan.
At the emergency of cercarias there is destruction of cells in the tubules; this destruction is more evident in L. palustris than in L. trun­catula. The undamaged tubules present a vicarious hypertrophy and the gland adopts a vesiculous aspect.

The comparison of results obtained in both molluscs confirms the role of L. truncatula as best host. However, as the cycle was sa­tisfactory completed in L. palustris it is very probable that it also in­tervenes actively as a vector of F. hepatica under normal conditions; this should be searched.