The impact of introduced hosts on parasite transmission: opisthorchiid infections in American mink (Neovison vison)

An invasive ant increases deformed wing virus loads in honey bees

The majority of invasive species are best known for their effects as predators. However, many introduced predators may also be substantial reservoirs for pathogens. Honey bee-associated viruses are found in various arthropod species including invasive ants. We examined how the globally invasive Argentine ant (Linepithema humile), which can reach high densities and infest beehives, is associated with pathogen dynamics in honey bees. Viral loads of deformed wing virus (DWV), which has been linked to millions of beehive deaths around the globe, and black queen cell virus significantly increased in bees when invasive ants were present. Microsporidian and trypanosomatid infections, which are more bee-specific, were not affected by ant invasion. The bee virome in autumn revealed that DWV was the predominant virus with the highest infection levels and that no ant-associated viruses were infecting bees. Viral spillback from ants could increase infections in bees. In addition, ant attacks could pose a significant stressor to bee colonies that may affect virus susceptibility. These viral dynamics are a hidden effect of ant pests, which could have a significant impact on disease emergence in this economically important pollinator. Our study highlights a perhaps overlooked effect of species invasions: changes in pathogen dynamics.

Invading parasites: spillover of an alien nematode reduces survival in a native species

It is widely assumed that spillover of alien parasites to native host species severely impacts naïve populations, ultimately conferring a competitive advantage to invading hosts that introduced them. Despite such host-switching events occurring in biological invasions, studies demonstrating the impact of alien macroparasites on native animal hosts are surprisingly few. In Europe, native red squirrels (Sciurus vulgaris) are replaced by introduced North American grey squirrels (S. carolinensis) mainly through resource competition, and, only in the United Kingdom and Ireland, by competition mediated by a viral disease. In Italy such disease is absent, but spillover of an introduced North American nematode (Strongyloides robustus) from grey to red squirrels is known to occur. Here, we used long-term (9 years) capture-mark-recapture and parasitological data of red squirrels in areas co-inhabited by grey squirrels in Northern Italy to investigate the impact of this alien helminth on naïve native squirrels’ body mass, local survival, and reproduction of females. We found no negative effect of the alien parasite on body mass or reproductive success, but intensity of infection by S. robustus reduced survival of both male and female squirrels. Significantly, survival of squirrels co-infected by their native nematode, Trypanoxyuris sciuri, was less affected by S. robustus, suggesting a protective effect of the native helminth against the new infection. Hence, we demonstrate that alien S. robustus spillover adds to the detrimental effects of resource competition and stress induced by grey squirrels, further reducing the fitness of the native species in the presence of the invasive competitor.

Helminths of Mustelids with Overlapping Ecological Niches: Eurasian Otter Lutra Lutra (Linnaeus, 1758), American Mink Neovison Vison Schreber, 1777, and European Polecat Mustela Putorius Linnaeus, 1758

This study presents the helminthological data on three mustelid species with overlapping ecological niches in Lithuania. In general, 14 helminth species or higher taxa were reported from all mustelids: Isthmiophora melis, Strigea strigis metacercariae, Pseudamphistomum truncatum, Alaria alata mesocercariae, Phyllodistomum folium, Opisthorchis felineus, Metametorchis skrjabini, Mesocestoides sp., Taenia martis, Aonchotheca putorii, Crenosoma schachmatovae, Eucoleus aerophilus, Molineus patens, and Nematoda g. sp. The largest number of helminths was detected in M. putorius (11) and N. vison (10) from wetlands; 7 helminths were detected in M. putorius from forests, and 8 in N. vison and 4 in L. lutra from water bodies. Habitat-related differences were found in the abundance and prevalence of E. aerophilus in M. putorius. M. putorius has higher indices of infection by I. melis, S. strigis metacercariae, and E. aerophilus compared to N. vison in wetlands. Differences in the abundance and prevalence of P. truncatum among N. vison and L. lutra in water bodies have been observed. Helminths detected in N. vison in the present study are native European parasites.

The American mink (Neovison vison) is a competent host for native European parasites

The American mink (Neovison vison) is a mustelid native to North America that was introduced in Europe and the former USSR for fur farming. Throughout the last century, accidental or deliberate escapes of mink from farms caused the establishment of stable feral populations. In fact, the American mink is considered an invasive alien species in 28 European countries. The present study evaluates the gastrointestinal and cardiopulmonary helminth fauna of the American mink in Galicia (NW Spain) to understand its role as a potential reservoir for parasites affecting other autochthonous mustelids. In the period 2008-2014, fifty American mink (35 males and 15 females) of different ages (22 immature and 28 adults) from the provinces of Lugo, Ourense and Pontevedra were captured and sacrificed. Eight parasite species were found (6 nematodes and 2 trematodes) with the following prevalences: Molineus patens (68%), Aonchotheca putorii (54%), Crenosoma melesi (10%), Aonchotheca annulosa (8%), Angiostrongylus daskalovi (6%), Aelurostrongylus spp. (2%), Troglotrema acutum (2%) and an unidentified trematode (2%). Eighty-two per cent of the mink harboured helminths, including 15 animals (30%) infected by only one parasite species, 19 (38%) by two species, 5 (10%) by three species and 2 mink (4%) by four species. All helminth species identified are native to European mustelids. Statistical models were used to evaluate if animal characteristics (age, sex and weight), date and capture area influenced the prevalence, intensity or parasite richness. Statistical differences were detected only in models for intensity of M. patens, A. putorii and C. melesi. This is the first report of Angiostrongylus daskalovi, a cardiopulmonary nematode, and A. annulosa, a gastrointestinal nematode specific of rodents, in American mink. Moreover, although the fluke T. acutum has already been cited in American mink, to our knowledge, the present study represents the first report of this trematode in the lung.