Aim: Exotic species may serve as vectors for the introduction of parasites from their native range and may also become infected by parasites already present in invaded areas, but the total number of parasites infecting such exotic species in their invaded areas is typically less than that in their native range. We tested whether the diversity of parasites associated with exotic species in the native and invaded areas is related to the epizootic impact these parasites cause. Location: Global. Methods: We examined the diversity and epizootic impact of 384 parasite taxa associated with 22 exotic freshwater invertebrate species. The epizootic impact of each parasite was rated based on whether it had been documented to cause a major pathological impact on a large proportion of an infected host population (other than the invader under consideration). Results: The total number of parasites associated with an exotic host in its native range was about twice that of all parasites associated with it in its entire invaded range. This was mainly because of the loss in the invaded areas of low impact parasites, whereas the average number of high impact parasites per host in these areas did not differ statistically from that in the native range. Main conclusions: Our study suggests similar levels of adverse impact of parasites of exotic species in both their native and invaded areas. In addition to the introduction of highly pathogenic exotic parasites, other mechanisms that may be involved include (1) acquisition by the invaders of new high impact parasites in the invaded ranges, (2) high abundance of the invaders in their new ranges and (3) susceptibility of novel hosts to exotic parasites because of the ‘naive host syndrome’.
Diversity and Distributions (2010) 16: 798–803

This study provides field evidence in support of the “parasite spillback hypothesis” that predicts a positive numerical response of native parasites to the presence of an exotic host that is competing for these parasites with native hosts.We examined the role that the exotic mollusc Dreissena polymorpha (zebra mussel) plays as the second intermediate host of the echinostomatid trematode Echinoparyphium recurvatum in Lake Naroch, Belarus. We found that due likely to the disproportionately high abundance of its novel exotic host, the metacercarial stage of this parasite has become substantially more abundant than that of other echinostomatid trematodes recorded in native molluscs. This finding suggests an increased load (the “spillback”) of E. recurvatum on native waterfowl that serve as its final hosts. The risk of aquatic birds becoming infected with this trematode via feeding on D. polymorpha was found to vary both spatially and seasonally. This risk was particularly high in the autumn at a depth of 2 m and at sites of bird gatherings.
Parasitology Research (2010) 106: 667–675