After numerous reports the local press about the “stinging water” in created on the Dzierżęcinka River—Water Valley reservoir and recognizing in bathers the symptoms of swimmers’ itch, environmental study on the presence of bird schistosome larvae in snail hosts was conducted. Snails belonging to Lymnaeidae and Planorbidae were collected at two sites: (i) part of anthropogenic reservoir (192 individuals) and (ii) the river part (37 individuals). Higher prevalence of Digenea was observed in snail populations living in Water Valley (29.8 %) compared to Dzierżęcinka River (21.3 %). The larvae of bird schistosomes were recorded in both localities in 1.8 % of collected snails. The prevalence of bird schistosomes reached 2.9 % in Planorbarius corneus, 2.8 % in Radix auricularia, and 5.9 % in Radix balthica/labiata. Laboratory tests have shown that at 19 °C the number of bird schistosome cercariae released from snail hosts significantly exceeded the number of cercariae of other identified Digenea species. It is worth underlining that despite the low prevalence of bird schistosomes, the high number of released cercariae was sufficient to create a real threat of swimmers’ itch in bathers. As indicated by the example presented, anthropogenic reservoirs create excellent conditions for Digenea species including bird schistosomes. In view of the real risk of people using the waters, tests on presence of the parasites in snail hosts should be included to the standard procedure of security control in bathing places.

Swimmer’s itch is a re-emerging human disease caused by bird schistosome cercariae, which can infect bathing or working people in water bodies. Even if cercariae fail after penetrating the human skin, they can cause dangerous symptoms in atypical mammal hosts. One of the natural methods to reduce the presence of cercariae in the environment could lie in the introduction of non–host snail species to the ecosystem, which is known as the “dilution” or “decoy” effect. The caenogastropod Potamopyrgus antipodarum—an alien in Europe—could be a good candidate against swimmer’s itch because of its apparent resistance to invasion by European bird schistosome species and its high population density. As a pilot study on this topic, we have carried out a laboratory experiment on how P. antipodarum influences the infestation of the intermediate host Radix balthica (a native lymnaeid) by the bird schistosome Trichobilharzia regenti. We found that the co–exposure of 200 P. antipodarum individuals per one R. balthica to the T. regenti miracidia under experimental conditions makes the infestation ineffective. Our results show that a non–host snail population has the potential to interfere with the transmission of a trematode via suitable snail hosts.

Biological invasions are commonly observed in both the natural habitats and those which are altered by human activities. An understanding of the mechanisms involved in the successful introduction, establishment and invasion of exotic taxa is essential in

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Parasite diagnostics were carried out on 11 Polish populations of Cepaea spp. In three of them, coming from the roadside ditches of a village (Rytel, northern Poland), very high (up to 60%) prevalence of Brachylaima mesostoma was observed. This study provides the first molecular evidence of the presence of B. mesostoma inside Cepaea spp. in Europe. In a few snails from a population found in a private garden in a small town (Chełmża, northern Poland), larvae of Brachylecithum sp. were present. Cercariae and/or metacercariae of B. mesostoma were observed in both species of Cepaea: C. hortensis and C. nemoralis, whereas larvae of Brachylecithum sp. were found only in C. nemoralis. Both species of parasites inhabited snail hepatopancreas whose structure was significantly damaged by larvae. There was no significant connection between parasite invasion and snail host morphotype. The research did not allow the reasons for the high prevalence of B. mesostoma in Cepaea spp. to be explained, and also did not explicitly indicate how the parasite invaded Cepaea spp. individuals making them, at the same time a second intermediate host. However, it poses important questions about the life cycle of the parasite that may threaten extensively kept small-size farms of poultry.

The aim of this work was to determine the diversity and the prevalence of trematodes from subclasses Digenea and Aspidogastrea in native unionid clams (Unionidae) and in dreissenid mussels (Dreissenidae) residing on the surface of their shells. 914 individuals of unionids and 4,029 individuals of Dreissena polymorpha were collected in 2014 from 11 lakes of the Polish Lowland. The total percentage of infected Unionidae and Dreissenidae was 2.5% and 2.6%, respectively. In unionids, we found three species of trematodes: Rhipidocotyle campanula (Digenea: Bucephalidae), Phyllodistomum sp. (Digenea: Gorgoderidae) and Aspigdogaster conchicola (Aspidogastrea: Aspidogastridae). Their proportion in the pool of the infected unionids was 60.9%, 4.4% and 13.0%, respectively. We also found pre-patent invasions (sporocysts and undeveloped cercariae, 13.0%) and echinostome metacercariae (8.7%) (Digenea: Echinostomatidae). The majority of infected Dreissena polymorpha was invaded by echinostome metacercariae (98.1%) and only in a few cases we observed pre-patent invasions (bucephalid sporocysts, 1.9%). The results indicate that in most cases unionids played the role of the first intermediate hosts for digenetic trematodes or final hosts for aspidogastrean trematodes, while dreissenids were mainly the second intermediate hosts.

No effective method has yet been developed to prevent the threat posed by the emerging disease—cercarial dermatitis (swimmer’s itch), caused by infective cercariae of bird schistosomes (Digenea: Schistosomatidae). In our previous studies, the New Zealand mud snail—Potamopyrgus antipodarum (Gray, 1853; Gastropoda, Tateidae)—was used as a barrier between the miracidia of Trichobilharzia regenti and the target snails Radix balthica. Since the presence of non-indigenous snails reduced the parasite prevalence under laboratory conditions, we posed three new research questions: (1) Do bird schistosomes show totally perfect efficacy for chemotactic swimming behavior? (2) Do the larvae respond to substances emitted by incompatible snail species? (3) Do the excretory-secretory products of incompatible snail species interfere with the search for a compatible snail host? The experiments were carried out in choice-chambers for the miracidia of T. regenti and T. szidati. The arms of the chambers, depending on the variant, were filled with water conditioned by P. antipodarum, water conditioned by lymnaeid hosts, and dechlorinated tap water. Miracidia of both bird schistosome species chose more frequently the water conditioned by snails—including the water conditioned by the incompatible lymnaeid host and the alien species, P. antipodarum. However, species-specific differences were noticed in the behavior of miracidia. T. regenti remained more often inside the base arm rather than in the arm filled with water conditioned by P. antipodarum or the control arm. T. szidati, however, usually left the base arm and moved to the arm filled with water conditioned by P. antipodarum. In conclusion, the non-host snail excretory-secretory products may interfere with the snail host-finding behavior of bird schistosome miracidia and therefore they may reduce the risk of swimmer’s itch.