Lymnaea palustris and Lymnaea fuscus are potential but uncommon intermediate hosts of Fasciola hepatica in Sweden

Abstract

BackgroundLymnaea palustris and L. fuscus are members of the European stagnicolines (Gastropoda: Lymnaeidae). The role of stagnicolines in transmission of Fasciola hepatica has been often proposed. To assess the possible relationship between these two stagnicolines and F. hepatica in Sweden, field monitoring in parallel with experimental infections of L. palustris and L. fuscus were conducted.MethodsStagnicoline snails were collected and identified on pastures grazed by either sheep or cattle on four farms suffering from fasciolosis in Sweden during 2011–2012. Field-collected L. palustris and L. fuscus were examined for F. hepatica DNA by PCR. In the laboratory, different age groups of L. palustris, L. fuscus and G. truncatula were each exposed to two F. hepatica miracidia and main infection characteristics were obtained.ResultsOne field-collected L. palustris (out of n = 668) contained F. hepatica as determined by PCR. On the other hand, stagnicolines artificially exposed to F. hepatica miracidia resulted in successful infection with fully differentiated cercariae, but only in juvenile snails (size, 1–2 mm at exposure) and with a prevalence of 51% and 13% in L. palustris and L. fuscus, respectively. In contrast, 90% of juvenile (size, 1–2 mm) and 92% of preadult G. truncatula (size, ≥ 2-4 mm), respectively, were successfully infected. Delayed, reduced and/or no spontaneous cercarial shedding was observed in the two stagnicolines when compared to G. truncatula. However, at snail dissection most cercariae from L. fuscus and L. palustris were able to encyst similarly to those from G. truncatula.ConclusionBoth L. fuscus and L. palustris can sustain larval development of F. hepatica but with an apparent level of age resistance. The finding of a single F. hepatica positive specimen of L. palustris, together with infection characteristics from the experimental infection, suggest that L. palustris is a more suitable snail vector of F. hepatica than L. fuscus. The reduced growth observed in both stagnicolines was contrary to the ‘parasitic gigantism’ theory. Overall, it seems that the epidemiological role of L. palustris in transmission of F. hepatica in Sweden is likely to be much lower than for G. truncatula.

Transmission patterns of Fasciola hepatica to ruminants in Sweden

“…Whenever F. hepatica-positive pooled samples were 155 identified, all individual samples were re-tested using the same PCR protocol. The specificity and the 156 sensitivity of the PCR method have already been tested in previous study (Novobilský et al, 2013). 157…”

Freshwater population of Ulva flexuosa (Ulvaceae, Chlorophyta) as a food source for great pond snail: Lymnaea stagnalis (Mollusca, Lymnaeidae)

“…It is crucial to note that L. stagnalis is a very important intermediate host of parasites, especially of the liver fluke ( Fasciola hepatica L.) (Novobilský et al . ), which should be kept in mind when using freshwater U. flexuosa as an alternative food source for humans.…”

Longitudinal study on the temporal and micro-spatial distribution of Galba truncatula in four farms in Belgium as a base for small-scale risk mapping of Fasciola hepatica

“…On the other hand, in Zoersel we found other snail species such as Succinea sp. in a higher relative proportion, and other snail species naturally infected with F. hepatica have been recently documented [4,5,34,35]. It has been suggested these species may play an important role in transmission when G. truncatula is not abundant [36].…”

“…Although several aquatic snail species have been reported as intermediate hosts for F. hepatica in Western Europe [3][4][5], Galba truncatula is considered to be by far the most important.…”