Each coin has 2 sides: a positive role of alien Potamopyrgus antipodarum (Grey, 1843) snails in reducing the infection of native lymnaeids with trematodes.

The change in the distribution of organisms in freshwater ecosystems due to natural or manmade processes raises the question of the impact of alien species on local communities. Although most studies indicate a negative effect, the positive one is more difficult to discern, especially in multispecies systems, including hosts and parasites. The purpose of the study was to check whether the presence of an alien host, Potamopyrgus antipodarum, reduces the intensity of Echinoparyphium aconiatum metacercariae in a native host, Radix spp. We additionally tested the impact of water temperature and the biomass of the alien host on the dilution effect. We experimentally studied (1) the lifespan of echinostome cercariae in different temperatures, (2) the infectivity of cercariae toward the alien host and native host, and (3) the impact of different biomass of the alien host on the intensity of metacercariae in the native host. We found that cercarial survival and infectivity were temperature dependent. However, cercarial survival decreased with increasing temperature, contrary to cercarial infectivity. Echinostome cercariae entered the renal cavity of both the native host and alien host, and successfully transformed into metacercariae. The number of metacercariae in the native host decreased with the increasing biomass of the alien host. Our results indicate that lymnaeids may benefit from the co-occurrence with P. antipodarum, as the presence of additional hosts of different origins may reduce the prevalence of parasites in native communities. However, the scale of the dilution effect depends not only on the increased spectrum of susceptible hosts but also on the other variables of the environment, including water temperature and host density.

Thinking "outside the box": The effect of nontarget snails in the aquatic community on mollusc-borne diseases.

There is a great need to understand the impact of complex communities on the free-living parasite stages that are part of them. This task becomes more complex as nonnative species emerge, changing existing relationships and shaping new interactions in the community. A relevant question would be: Can the coexistence of nontarget snails with the target hosts contribute to trematodasis control? We used field and experimental approaches to investigate nonnative competitor-induced parasite dilution. During a three-year field study, we investigated digenean infection in Lymnaea stagnalis from eight Polish lakes inhabited or uninhabited by Potamopyrgus antipodarum. Additionally, we verified the presence of digenean infections in the populations of P. antipodarum. Moreover, we conducted an experimental infection of L. stagnalis with miracidia of Trichobilharzia szidati under increasing densities of P. antipodarum and aimed to infect P. antipodarum with them separately. The prevalence of avian schistosomes in lymnaeid snails was significantly higher in uninhabited lakes than in lakes inhabited by P. antipodarum. Our study indicates that waters with a higher density of invaders have a lower prevalence of avian schistosomes in lymnaeid hosts. The results of experimental studies confirmed that the presence of high densities of P. antipodarum reduces the probability of target host infection. Both field and experimental studies rule out the role of P. antipodarum as a source of avian schistosome cercariae. Here, a nonnative species was tested as a diluter, which in practice may be harmful to the local environment. This work is not a call for the introduction of nonnative species; it is intended to be a stimulus for researchers to continue searching for natural enemies of parasites because, as our results show, they exist. Finding natural enemies to the most dangerous species of human and animal parasites that will pose no threat to the local environment could be groundbreaking.

Life history strategies of Cotylurus spp. Szidat, 1928 (Trematoda, Strigeidae) in the molecular era - Evolutionary consequences and implications for taxonomy.

Species of Cotylurus Szidat, 1928 (Diplostomoidea: Strigeidae) are highly specialized digeneans that parasitize the gastrointestinal tract and bursa of Fabricius of water and wading birds. They have a three-host life cycle; the role of first intermediate host is played by pulmonate snails, while a wide range of water snails (both pulmonate and prosobranch) and leeches are reported as second intermediate hosts. Unfortunately, species richness, molecular diversity and phylogeny of metacercariae of Cotylurus spp. (tetracotyle) occurring in snails remain poorly understood. Thus, we have performed the parasitological and taxonomical examination of tetracotyles form freshwater snails from Poland, supplemented with adult Strigeidae specimens sampled from water birds. In this study we report our use of recently obtained sequences of two molecular markers (28S nuclear large ribosomal subunit gene (28S rDNA) and the cytochrome c oxidase subunit 1 (CO1) fragment), supplemented by results of a method of species delimitation (GMYC) and haplotype analysis to analyse some aspects of the ecology, taxonomy, and phylogeny of members of the genus Cotylurus. The provided phylogenetic reconstructions discovered unexpectedly high molecular diversity within Cotylurus occurring in snails, with clearly expressed evidence of cryptic diversity and the existence of several novel-species lineages. The obtained results revealed the polyphyletic character of C. syrius Dubois, 1934 (with three separate molecular species-level lineages) and C. cornutus (Rudolphi, 1809) Szidat, 1928 (with four separate molecular species-level lineages). Moreover, we demonstrated the existence of two divergent phylogenetical and ecological lineages within Cotylurus (one using leeches and other snails as second intermediate hosts), differing significantly in their life history strategies.

Ketogenic diet impairs neurological development of neonatal rats and affects biochemical composition of maternal brains: evidence of functional recovery in pups.

The ketogenic diet (KD) is a type of diet in which the intake of fats significantly increases at the cost of carbohydrates while maintaining an adequate amount of proteins. This kind of diet has been successfully used in clinical therapies of drug-resistant epilepsy, but there is still insufficient evidence on its safety when used in pregnancy. To assess KD effects on the course of gestation and fetal development, pregnant females were fed with: (i) KD during pregnancy and lactation periods (KD group), (ii) KD during pregnancy replaced with ND from the day 2 postpartum (KDND group) and (iii) normal diet alone (ND group). The body mass, ketone and glucose blood levels, and food intake were monitored. In brains of KD-fed females, FTIR biochemical analyses revealed increased concentrations of lipids and ketone groups containing molecules. In offspring of these females, significant reduction of the body mass and delays in neurological development were detected. However, replacement of KD with ND in these females at the beginning of lactation period led to regainment of the body mass in their pups as early as on the postnatal day 14. Moreover, the vast majority of our neurological tests detected functional recovery up to the normal level. It could be concluded that the ketogenic diet undoubtedly affects the brain of pregnant females and impairs the somatic and neurological development of their offspring. However, early postnatal withdrawal of this diet may initiate compensatory processes and considerable functional restitution of the nervous system based on still unrecognized mechanisms.

Invaders as Diluents of the Cercarial Dermatitis Etiological Agent.

Research on alien and invasive species focuses on the direct effects of invasion on native ecosystems, and the possible positive effects of their presence are most often overlooked. Our aim was to check the suitability of selected alien species (the snail Physa acuta, the bivalve Dreissena polymorpha, and the gammarid Dikerogammarus villosus) as diluents for infectious bird schistosome cercariae-the etiological factor of swimmer's itch. It has been hypothesized that alien species with different feeding habits (scrapers, filterers and predators) that cohabit the aquatic environment with intermediate hosts of the schistosomatid trematodes are capable of feeding on their free-swimming stages-cercariae. In the laboratory conditions used, all experimental animals diluted the cercariae of bird schistosome. The most effective diluents were P. acuta and D. villosus. However, a wide discrepancy in the dilution of the cercariae between replicates was found for gammarids. The obtained results confirm the hypothesis that increased biodiversity, even when alien species are involved, creates the dilution effect of the free-living stages of parasites. Determining the best diluent for bird schistosome cercariae could greatly assist in the development of current bathing areas protection measures against swimmer's itch.

The chemotactic swimming behavior of bird schistosome miracidia in the presence of compatible and incompatible snail 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.

Cepaea spp. as a source of Brachylaima mesostoma (Digenea: Brachylaimidae) and Brachylecithum sp. (Digenea: Dicrocoeliidae) larvae in Poland.

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 (Chelmza, 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.

Agents of swimmer's itch-dangerous minority in the Digenea invasion of Lymnaeidae in water bodies and the first report of Trichobilharzia regenti in Poland.

Trichobilharzia spp. have been identified as a causative agent of swimmers' itch, a skin disease provoked by contact with these digenean trematodes in water. These parasites have developed a number of strategies to invade vertebrates. Since we have little understanding of the behavior of these parasites inside the human body, the monitoring of their invasion in snail host populations is highly recommended. In our research, lymnaeid snails were collected from several Polish lakes for two vegetation seasons. The prevalence of bird schistosomes in snail host populations was significantly lower than that of other digenean species. We were the first to detect the presence of the snails emitted Trichobilharzia regenti (potentially the most dangerous nasal schistosome) in Poland. In addition, by sequencing partial rDNA genes, we confirmed the presence of the snails positive with Trichobilharzia szidati in Polish water bodies, showing that swimmer's itch is more frequent during summer months and that large snails are more often infected with bird schistosomes than small ones.

Potamopyrgus antipodarum as a potential defender against swimmer's itch in European recreational water bodies-experimental study.

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.

Infection of Potamopyrgus antipodarum (Gray, 1843) (Gastropoda: Tateidae) by trematodes in Poland, including the first record of aspidogastrid acquisition.

The prosobranch gastropod Potamopyrgus antipodarum (Gray, 1843) is poorly understood as a parasite host outside its native New Zealand, including in Europe. Our aim was to ascertain whether non-native P. antipodarum could acquire aspidogastrids or digeneans in habitats where these parasites are found in native hosts. We examined 2400 P. antipodarum individuals from Sosno Lake (Poland). The majority of snails were adult females. No males were found. We found five P. antipodarum individuals with Aspidogaster conchicola and 39 snails with metacercariae of Echinoparyphium aconiatum Dietz 1909 or E. recurvatum (Linstow, 1873). Snails with metacercariae and unparasitized snails, but not snails with A. conchicola, produced embryos. Ours is the first record of an Aspidogastrea - P. antipodarum association.

A morphological study of Diplodiscus subclavatus (Pallas, 1760) (Trematoda: Diplodiscidae) adults from the accidental host, Viviparus contectus (Millet, 1813) (Caenogastropoda: Viviparidae).

A phenomenon of switching of the parasite in the food chain to an accidental host is commonly observed in nature. However, there is little available data concerning the morphological descriptions of parasites that passively get into the atypical hosts and are capable, at least to some degree, of somatic growth and development of reproductive structures. A morphological survey of Diplodiscus subclavatus (Pallas, 1760) adults isolated from a digestive tract of an accidental host, Viviparus contectus (Millet, 1813), was carried out. Diplodiscus subclavatus individuals identified in prosobranch snails were morphologically similar to adult forms of the parasite described from amphibians, typical final hosts in the life cycle of this paramphistomid. The observed forms of D. subclavatus had a fully developed reproductive system, sperm in the seminal vesicle and oocytes in the ovary. The number of eggs in the uterus ranged from 3 to 17. Our research indicates that D. subclavatus individuals reach the sexual maturity in the accidental, invertebrate hosts.

The real threat of swimmers' itch in anthropogenic recreational water body of the Polish Lowland.

After numerous reports the local press about the "stinging water" in created on the Dzierzecinka 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 Dzierzecinka 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.

Symptoms of behavioural anapyrexia--reverse fever as a defence response of snails to fluke invasion.

The subject of the research was the thermal preferences of Planorbarius corneus individuals infected by larvae of digenetic trematodes. Snails were obtained over two consecutive years, 2009 and 2010, from 10 water bodies located in central Poland. The relationship between the seasons and the occurrence of patent invasions in hosts found in the shore-zone of lakes was observed. Behavioural experiments conducted on P. corneus individuals placed in a thermal gradient demonstrated that parasite infection had an impact on the thermal preferences of the snails. Individuals that shed cercariae of Bilharziella polonica, Cotylurus sp., Notocotylus ephemera, Rubenstrema exasperatum/Neoglyphe locellus, Rubenstrema opisthovitellinum, or Tylodelphys excavata displayed symptoms of behavioural anapyrexia, similarly to experimentally injured snails. This response increased the survival of infected individuals while simultaneously prolonging the period of shedding of dispersive forms of parasites. This point of view was upheld by the observation that infected snails bred at 19°C lived longer than at 26°C and the shedding rate of cercariae at a lower temperature was lower than at a higher one.