Elżbieta Żbikowska

Infection of snails with bird schistosomes and the threat of swimmer's itch in selected Polish lakes.

Studies of selected species of Lymnaeidae and Planorbidae showed that infection with bird schistosomes occurred in 14 of the 26 Polish lakes studied. In Planorbarius corneus larvae of Bilharziella polonica were found, and in Lymnaea stagnalis and Radix auricularia larvae of Trichobilharzia ocellata. In spite of their comparatively low prevalence, cercariae, potentially pathogenic to humans, may have caused dermatitis in patients registered in one of the regions under study. The low prevalence of infection among the host snails may have been compensated for by the enormous number of cercariae released by them, which, moreover, showed a long-lasting viability, particularly at low ambient temperature.

One hundred years of research on the natural infection of freshwater snails by trematode larvae in Europe

Research on the infection of snails by trematodes has been conducted in Europe for over a hundred years. The initial poor knowledge of the intra-molluscan stages of these parasites together with the difficulty of classifying them constituted a serious obstacle to the undertaking of integrated parasitological and malacological efforts to gain a better understanding of the phenomenon. The compilation of morphological and anatomical results of research on trematode larvae resulted in the publication of keys to designate species of parasites, but was not sufficient to encourage malacologists to collaborate with parasitologists. This paper undertakes to collect data published over the last hundred years on the natural infection of European populations of freshwater snails by trematode larvae. The aim of this undertaking is to make researchers of malacofauna and, above all, experts on freshwater snails aware of the scale of the problem of molluscs being exploited as intermediate hosts of trematodes and, consequently, to encourage parasitologists and malacologists to collaborate on this phenomenon that is crucial for both parasites and hosts.

One snail – three Digenea species, different strategies in host-parasite interaction

The mostly lab-based studies on snail-trematode interactions should be complemented by research on naturally invaded hosts. In this mini-review, three different ways of snail exploitation by Digenea larvae are presented. Morphological, physiological and behavioral changes caused by three parasites in the same naturally infected host – Lymnaea stagnalis – differ in species-dependent fashion. The impact of a snail-trematode interaction depends on parasite virulence (i.e. parasite induced lost of fitness of the host). The pathogenicity varies with the survival strategy of the invader. Sporocyst-born Plagiorchis elegans, which uses the same Lymnaea stagnalis individual as a first but also as a second intermediate host, does not disturb host processes as strongly as redia-born Echinoparyphium aconiatum. The third parasite species – Diplostomum pseudospathaceum, also sporocyst-born – is more virulent than P. elegans, but it can modify and relax host exploitation to overwinter in the snail. The data presented demonstrate that successful use of first intermediate host can be arranged in different ways.

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.

Is Nuphar lutea (L.) Sm. a structuring factor for macrozoobenthos and selected abiotic parameters of water and bottom sediments throughout the year

Studies on the role of nymphaeids in water bodies are uncommon, despite the fact that they often dominate in eutrophic lakes. Therefore, we decided to evaluate the effect of a nymphaeid Nuphar lutea on its environment. We hypothesised that its presence can increase the diversity and abundance of zoobenthos, as well as modify selected abiotic parameters, both during the growing season (in the presence of leaves) and outside it (with underground structures only). Three pairs of stations (within and outside Nuphar stands) were established in two shallow, eutrophic lakes and sampled monthly during an entire year. Zoobenthos taxon richness, biodiversity and total density were higher among nymphaeids throughout the year. On the other hand, total zoobenthos biomass was not affected by the presence of plants. Most macroinvertebrates reached higher densities within Nuphar stands, the most abundant being Polypedilum nubeculosum, Potamothrix bavaricus, Ephemeroptera and Ceratopogonidae. In turn, Potamothrix hammoniensis, Chaoborus sp. and Tanypus sp. were more abundant outside the stands. Other taxa, including the dominants (Chironomus sp., Procladius spp., Einfeldiadissidens, Valvatapiscinalis), were not affected by the presence of Nuphar. Nuphar did not influence water temperature, oxygen concentration, and conductivity, though sediments within the stands exhibited lower water content and higher proportion of large organic particles. Thus, Nuphar effect on macroinvertebrates was probably direct, through increased habitat heterogeneity, physical stability of substratum and food availability. Our study has shown that nymphaeids, despite their structural distinctness, can affect positively bottom fauna similarly to other morphological groups of plants.

Coexistence of Legionella pneumophila Bacteria and Free-Living Amoebae in Lakes Serving as a Cooling System of a Power Plant.

The study was aimed at determining whether potentially pathogenic free-living amoebae (FLA) and Legionella pneumophila can be found in lakes serving as a natural cooling system of a power plant. Water samples were collected from five lakes forming the cooling system of the power plants Pątnów and Konin (Poland). The numbers of investigated organisms were determined with the use of a very sensitive molecular method—fluorescence in situ hybridization (FISH). The result of the present study shows that thermally altered aquatic environments provide perfect conditions for the growth of L. pneumophila and amoebae. The bacteria were identified in the biofilm throughout the entire research period and in the subsurface water layer in July and August. Hartmanella sp. and/or Naegleria fowleri were identified in the biofilm throughout the entire research period.

Digenean larvae—the cause and beneficiaries of the changes in host snails’ thermal behavior

Parasite-induced changes in host’s thermal preferences not only can be interpreted as a physiological defense response of the host but also can represent a pathological manifestation of the parasite. Both may become established in host-parasite relationships if they are beneficial for at least one of the counterparts. This study investigates parasite-induced changes in the thermoregulatory behavior of first intermediate hosts of Digenea (i.e. Lymnaea stagnalis and Planorbarius corneus), infected with Notocotylidae or Echinostomatidae larvae. The investigated parasite species developed different transmission strategies outside the body of a snail, which may imply a different effect on the behavior of their hosts. Notocotylus attenuatus in L. stagnalis and Notocotylus ephemera in P. corneus produce symptoms of anapyrexia, prolonging the lifespan of their hosts. By contrast, Echinoparyphium aconiatum in L. stagnalis and Echinostoma spiniferum in P. corneus interfere with defensive thermoregulatory behavior of host snails, causing their accelerated death. The results of laboratory research indicate that thermal preferences of the snails infected with all investigated trematodes facilitate the transmission of the parasites in environment.

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.

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.

Ketoprofen-induced inhibition of symptoms of behavioural fever observed in wintering Planorbarius corneus (L.) (Gastropoda: Planorbidae)

Research on behavioural fever in Planorbarius corneus was undertaken using a longitudinal thermal gradient. Before the experiment, snails were acclimated at 19 °C. Following injections of lipopolysaccharide (LPS, a pyrogenic agent), ketoprofen (an antipyretic) or saline solution (control), thermal behaviour of the animals was automatically recorded for 48 h. The results demonstrated that LPS-induced symptoms of behavioural fever were inhibited by ketoprofen. Additionally, it was observed that snails which, before the injection of LPS, were preinjected with ketoprofen showed symptoms of behavioural fever with a 20-h delay. This result shows the inhibitory effect of ketoprofen on the occurrence of behavioural fever symptoms in P. corneus. It may suggest some similarity in mechanism of enhanced thermal preference in snails to vertebrate fever— both effectively inhibited by aspirin-like anti-inflammatory compounds.