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Typhlocoelum cucumerinum is a tracheal parasite of birds widely distributed across the globe. Nevertheless, aspects of the biology of this cyclocoelid are still poorly understood. Herein, we report the finding of T. cucumerinum in definitive and intermediate hosts from an urban waterbody of Brazil. The parasite was initially detected during the necropsy of domestic Muscovy ducks (Cairina moschata) found dead in the locality. Coproparasitological tests in live animals revealed that 12/47 (25.53%) Muscovy ducks and 2/8 (25%) mallards (Anas platyrhynchos platyrhynchos) were infected with T. cucumerinum. Moreover, rediae and metacercariae morphologically similar to T. cucumerinum were found in 3/248 (1.33%) Biomphalaria straminea collected in the same waterbody frequented by the birds. The conspecificity between the adult and the larval stages was confirmed molecularly (100% similarity in Cox-1). Moreover, the phylogenetic position of T. cucumerinum was determined for the first time based on partial fragments of the 28S, Cox-1 and Nad-1 genes. The species grouped with other members of the subfamily Typhlocoelinae with sequences available, but the data obtained do not support the distinctiveness of the genera Typhlocoelum and Tracheophilus. Further studies involving a broader range of species can result in taxonomic rearrangements in Typhlocoelinae.

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis affecting more than 200 million people in tropical and subtropical countries, infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The Aporocotylidae are pathogenic in fish, Spirorchiidae in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in molluscs and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive, but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

We report digeneans (Diplostomidae, Crassiphialinae) in the endangered freshwater fishes Valencia letourneuxi and Valencia robertae, endemics of Western Greece. Digenean metacercariae occurred in two forms in the abdominal cavity, excysted and encysted, the latter attached to the gonads, liver and alimentary tract. Parasites were, using morphological and molecular techniques, identified as two representatives of Crassiphialinae, specifically part of the Posthodiplostomum-Ornithodiplostomum clade. The spatial, seasonal, and age class variation in parasite prevalence was examined. Autumn parasite prevalence varied between the six populations sampled (18.2 to 100%). Seasonal prevalence at the two sites sampled quadannually peaked in autumn and reached its lowest value in spring; prevalence increased with size to 100% in young adult fish. We did not find a correlation between prevalence and host sex. Overall parasites' weight averaged 0.64% of the host's, while parasite weight increased with host weight. A comparison of relative condition and hepatosomatic and gonadosomatic indices of infected and metacercariae-free specimens showed that infection did not have a significant effect on host body condition and reproduction. Regarding the parasite's life cycle, planorbid gastropods are proposed as potential first intermediate hosts in view of the host's diet and occurrence data of molluscs in the ecosystem. This is the first record of a diplostomid digenean in valenciid fishes and of representatives of the Posthodiplostomum-Ornithodiplostomum clade in a native Greek freshwater fish. Our findings are discussed in conjunction to fish conservation interventions, since parasites may contribute to the decline of endangered species.

To identify trematode diversity and life-cycles in the sub-Arctic Lake Takvatn, Norway, we characterised 120 trematode isolates from mollusc first intermediate hosts, metacercariae from second intermediate host fishes and invertebrates, and adults from fish and invertebrate definitive hosts, using molecular techniques. Phylogenies based on nuclear and/or mtDNA revealed high species richness (24 species or species-level genetic lineages) and uncovered trematode diversity (16 putative new species) from five families typical in lake ecosystems (Allocreadiidae, Diplostomidae, Plagiorchiidae, Schistosomatidae and Strigeidae). Sampling potential invertebrate hosts allowed matching of sequence data for different stages, thus achieving molecular elucidation of trematode life-cycles and exploration of host-parasite interactions. Phylogenetic analyses also helped identify three major mollusc intermediate hosts (Radix balthica, Pisidium casertanum and Sphaerium sp.) in the lake. Our findings increase the known trematode diversity at the sub-Arctic Lake Takvatn, showing that digenean diversity is high in this otherwise depauperate sub-Arctic freshwater ecosystem and indicating that sub-Arctic and Arctic ecosystems may be characterised by unique trematode assemblages., (Copyright © 2017 Australian Society for Parasitology. All rights reserved.)

In the ecosystem of the Belaya River, fishes of the family Cyprinidae were infected with three epidemically important species oftrematodes of the family Opisthorchidae: Opisthorchisfelineus, Metorchis bilis, and Pseudamphistomum truncatumn. No biotopes of mollusks of the genus Codiella were detected. The contamination of underyearlings with-Ofelineus and M.bilis metacercariae indicates that there are cores of opisthorchiasis and metorchiasis (M.bifis) foci in the ecosystem of the lower course of the river. The presence of biotopes of the genus Bithynia mollusks, the first intermediate host.for P. truncatum, in the waters, but the absence of fishes infected with P.truncatum metacercariae among the examined under- yearlings may lead to the conclusion that there are no cores of pseudamphistomiasis foci. Infestation of onein 97 older individual muvarica (Albumus alburnus) with trematode metacercariae is evidence of its infection outside the floodplain river ecosystems of the Belaya River and subsequent migration of the fish into the lowerreaches of the river, where a barren zone of a pseudamphistomiass focus is formed. In this ecosystem there is a risk of human infection with epidemically important species of trematodes of the family Opisthorchidae (O.felineus, M.bifis, and P.truncatum)-when eating the fish caught in the river, its tributaries, and floodplain waterbodies. When identifying the metacercariae and detecting the natural foci of trematodes, it is necessary to take into account the fact that the fishes of the family Cyprinidae in the river ecosystem have four types of Opisthorchis metacercariae (after D.A.Razmashkin).

Overlapping distributions of hosts and parasites are critical for successful completion of multi-host parasite life cycles and even small environmental changes can impact on the parasite's presence in a host or habitat. The generalist Cardiocephaloides longicollis was used as a model for multi-host trematode life cycles in marine habitats. This parasite was studied to quantify parasite dispersion and transmission dynamics, effects of biological changes and anthropogenic impacts on life cycle completion. We compiled the largest host dataset to date, by analysing 3351 molluscs (24 species), 2108 fish (25 species) and 154 birds (17 species) and analysed the resultant data based on a number of statistical models. We uncovered extremely low host specificity at the second intermediate host level and a preference of the free-swimming larvae for predominantly demersal but also benthic fish. The accumulation of encysted larvae in the brain with increasing fish size demonstrates that parasite numbers level off in fish larger than 140mm, consistent with parasite-induced mortality at these levels. The highest infection rates were detected in host species and sizes representing the largest fraction of Mediterranean fishery discards (up to 67% of the total catch), which are frequently consumed by seabirds. Significantly higher parasite densities were found in areas with extensive fishing activity than in those with medium and low activity, and in fish from shallow lagoons than in fish from other coastal areas. For the first time, C. longicollis was also detected in farmed fish in netpens. Fishing generally drives declines in parasite abundance, however, our study suggests an enhanced transmission of generalist parasites such as C. longicollis, an effect that is further amplified by the parasite's efficient host-finding mechanisms and its alteration of fish host behaviour by larvae encysted in the brain. The anthropogenic impact on the distribution of trophically-transmitted, highly prevalent parasites likely results in a strong effect on food web structure, thus making C. longicollis an ideal bioindicator to compare food webs in natural communities versus those impacted by fisheries and aquaculture., (Copyright © 2016 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.)

Background: The cutaneous monostome trematode Collyriclum faba (Bremser in Schmalz, 1831) is a bird parasite with a hitherto unknown life cycle and highly focal occurrence across the Holarctic and Neotropic ecozones., Methods: Representative specimens of benthic organisms were sampled at multiple sites and dates within the known foci of C. faba occurrence in Slovakia. A combined approach involving detailed morphological examination and sequencing of two independent DNA loci was used for their analysis., Results: We elucidated the complete life cycle of C. faba, which we determined to include the aquatic gastropod mollusk Bythinella austriaca (Frauenfeld, 1857) as the first intermediate host, the mayflies of the family Heptageniidae, Ecdyonurus venosus (Fabricius, 1775) and Rhithrogena picteti Sowa, 1971 x iridina (Kolenati, 1839), as the second intermediate hosts, and birds (primarily but not exclusively passeriform birds) as the definitive hosts. Bythinella austriaca occurs focally in the springs of tributaries of the Danube in the Alpine-Carpathian region. The restricted distribution of B. austriaca explains the highly focal distribution of C. faba noticed previously in spite of the broad distribution of its second intermediate and definitive host species. Utilization of both larval and adult Ephemeroptera spp. as the second intermediate hosts explains the known spectrum of the definitive host species, with the highest prevalence in species feeding on larvae of Ephemeroptera, such as Cinclus cinclus (Linnaeus, 1758) and Motacilla cinerea Tunstall, 1771, or adults of Ephemeroptera, such as Sylvia atricapilla (Linnaeus, 1758) and Regulus regulus (Linnaeus, 1758). In this study, we also determine the prevalence and DNA sequences of other immature trematode specimens found in the examined benthic organisms (particularly the families Microphallidae, Troglotrematidae and Nanophyetidae and Euryhelmis zelleri Grabda-Kazubska, 1980, Heterophyidae), and describe cercariae of C. faba., Conclusions: We determined the full life cycle of the Central European populations of C. faba. We speculate that other species of Bythinella and the closely related genus Amnicola may serve as first intermediate hosts in other parts of the distribution range of C. faba. Similarly, other Ephemeroptera of the family Heptageniidae may serve as the second intermediate hosts of C. faba in the Americas.

Cercariae are non-feeding free-living stages in the life cycles of trematodes, highly influenced by temperature. Their life span is brief, limited by the depletion of a non-renewable glycogen store. Warmer temperatures under the influence of climate change may promote the transmission of parasites and therefore understanding their thermobiology forms an important step in discerning the future dynamics of parasite populations. An empirical relationship exists between cercarial mean expected life span and the half-life of the population (t0·5) and therefore t0·5 is a good indicator of glycogen utilization. In this study experimental data on the effects of temperature on cercarial survival is compiled from the scientific literature and evaluated in terms of metabolism using Q10 and Arrhenius activation energy (E* or μ), common measures of temperature-mediated reaction rates. Cercariae have a variable response to temperature, which does not appear to be influenced by their life-history attributes or size. There were little differences in Q10 and E* values between most temperature ranges. In almost half the studies examined (7 of 16) cercariae demonstrated a discrete zone of thermostability over a range equivalent to typical individual mean summer temperatures. Distinct intraspecific differences in temperature responses between 3 laboratory strains of Schistosoma mansoni and 2 natural strains of Echinoparyphium recurvatum sensu stricto were apparent. The importance of these results for cercarial biology under global climate change is discussed.

Centrocestusformosanus is a zoonotic trematode from Asia and has been mainly associated as cause of death of cultured fish. To identify pathogen trematode species in tilapia fry (Oreochromis niloticus) and to determine mollusks hosting these parasites, freshwater mollusks were collected from tilapia cultured ponds and experimental infections were carried out with tilapia fries and different mollusk species. A total of 907 freshwater mollusks were obtained from tilapia ponds and were identified to species level, four gastropods and one bivalve were determined: Melania tuberculata, Melanoides turricula, Pomacea flagellata, Haitia cubensis and Anodontiles luteola. For the first time, the presence of M. turricula and H. cubensis are reported in Costa Rica. Seven morphotypes of cercariae (Xifiodiocercaria, Equinostoma, Oftalmocercaria, Parapleurolofocercus, Cistocerca, Furcocercaria and Leptocercaria) parasitizing all five species of mollusks were found, all of distome type. Experimental exposure of tilapia fry to M. tuberculata demonstrated that the parapleurolofocercus morphotype found in the mollusk is in accordance with the finding of C. formosanus in tilapia fry. An abundance and mean intensity of 1018-1027 digeneans per gill in each exposed fish was determined. Centrocestus formosanus is reported for the first time in Costa Rica, for which the primary and secondary intermediate hosts were also determined.

During the period from January to December (2007), 1,095 freshwater molluscs of four species were captured (Lymnaea stagnalis, Stagnicola elodes, Physella cubensis and Physa acuta) in Lake Chicnahuapan, State of Mexico, Mexico. Two hundred seventy-two (24.84% prevalence) of these molluscs were parasitised by 11 trematode species (from which two were not identified at the species level) having six cercariae species and five metacercariae species represented in five families. The cercariae Telorchis corti (Plagiorchiidae) and the metacercariae Cotylurus cornutus (Strigeidae) were the species with the highest prevalence among the examined snails. The highest percentage of infection was observed in L. stagnalis (27.45% of prevalence, n = 572) and P. cubensis (23.96%, n = 455). Twenty-one of the examined snails had multiple infections with up to three trematode species.

The morphology of a type specimen of Lophotaspis orientalis Faust and Tang, 1936 (Aspidogastrea: Aspidogasteridae) was compared with the morphology of the original description of L. corbiculae Moriya, 1944 and of newly collected specimens from Corbicula species in China and Japan. The original description of L. orientalis was revised by the re-examination of the type specimen. Consequently, some key characteristics of these two species described by Moriya (1944) became invalid. The gonad size of the L. orientalis type specimen was out of the range of all other investigated specimens and past records, suggesting that the L. orientalis type specimen (host: soft-shell turtle) is a different species from the other investigated specimens (host: freshwater clam).

Quantitative estimation of the trematode Schistogonimus rarus at the stage of cercaria is carried out in the ecosystem of the Malye Chany lake, south of Western Siberia, on the base of long-term data obtained in 1995-2002. Average daily emission of the S. rarus cercaria was shown to be significantly higher in larger mollusc hosts (p < 0.01), by the results of laboratory investigations. Moreover, significant decrease of the average daily emission of the S. rarus cercaria from June to July is established (p < 0.01). It was revealed, that emission of the S. rarus cercaria in the south of Western Siberia (both in natural and laboratory conditions) lasts no more than 50 days and is finished in August. The infestation rate of the mollusc host Bithynia troschelii by the S. rarus parthenites varied from 0.28 to 1.44 % in different years and correlated with the water temperature at first ten days of June (r = 0.75). Flow of the S. rarus cercaria (specimens per square meter) was estimated on the base of the quantitative characteristics of the cercaria emission, data on the infestation rate of the host population, and data on the host abundance. The flow of the cercaria varied from 6000 (in 1998) up to 330000 (in 2000) per season and correlated with the water temperature in third ten days of June (r = 0.71).

Sporocycts of the "pygmaeus" microphallides (Microphallus piriformes) are localized in hepatopancreas and gonads of Littorina molluscs causing total parasitic castration. A histological study of penial glands in Littorina saxatilis and L. obtusata males infested with trematodes M. piriformes has been made. Copulatory organs of noninfested molluscs, molluscs after recent contamination (with not completely formed daughter sporocysts), and molluscs containing mature metacercariae inside daughter sporocysts were examined. Based on the data obtained, probable dynamics of the histological structure of infested glandular apparatus was established. It was shown, that the trematode infestation have an influence on the muscular and secretory parts of penial glands. The wall of the penial gland muscular capsule becomes more fine in infested L. saxatilis. On the contrary, this wall is vastly thicker in infested L. obtusata, as compared with noninfested individuals. Glandular cells of the molluscs' penial glands decreases the amount of granular secret in both species. In L. obtusata the number of secretory cells is shown to be reduced up to their total disappearance. The above pathological changes probably prevent normal function of penial glands.

Attention is drawn to the effects of parasites on their hosts, taking as a model the digenean parasites of teleosts (hereafter: fish) from lagoons along the French Mediterranean coast. Because digeneans have a heteroxenic life cycle, their impact is not limited to the definitive host, which harbours the sexual adults, but is extended to the first host (mollusc) and to the second host ("invertebrate" or fish). Adult parasites, in order to ensure efficient sexual reproduction, never cause excessive damage to their definitive host, usually only exploiting the intestinal fluids; however, the host must intensify its search for prey, which results in a diminished fitness. Within the first host, 'larval' stages of digenean parasites invade the gonads, resulting in its castration, then exhaustion and eventually death. The diversion of energy from the second hosts towards the parasites forces them to intensify their search for food, resulting in decreased fitness and an increased risk of being eaten; in addition, manipulation of the host's behaviour by parasites drives this host into the food chain of the definitive host. In lagoons, many individuals of almost all species of fish and invertebrates act as first, second and/or definitive hosts for digeneans. Obviously, parasites have a severe impact on the population dynamics of key taxa, on the food web and therefore also on the functioning of the whole lagoon ecosystem. Yet this impact has been largely overlooked or underestimated in functioning models, by ecologists, who tend to prioritize more apparent trophic relationships.

Waterborne trematode and protozoan infections inflict considerable morbidity on healthy, i.e., immunocompetent people, and may cause life-threatening diseases among immunocompromised and immunosuppressed populations. These infections are common, easily transmissible, and maintain a worldwide distribution, although waterborne trematode infections remain predominantly confined to the developing countries. Waterborne transmission of trematodes is enhanced by cultural practices of eating raw or inadequately cooked food, socio-economical factors, and wide zoonotic and sylvatic reservoirs of these helminths. Waterborne protozoan infections remain common in both developed and developing countries (although better statistics exist for developed countries), and their transmission is facilitated via contacts with recreational and surface waters, or via consumption of contaminated drinking water. The transmissive stages of human protozoan parasites are small, shed in large numbers in feces of infected people or animals, resistant to environmental stressors while in the environment, and few are (e.g., Cryptosporidium oocysts) able to resist standard disinfection applied to drinking water.

In the context of the present-day teaching of parasitocenoses and the proposition that the pathogen's population is the only compulsory and specific component of a natural focus, the author discloses the ecological bases of the combination of natural foci of opisthorchiasis and methorchiasis (M. bilis), methorchiasis (M. bilis) and methorchiasis (M. xanthosomus). These foci are host population-combined. While analyzing the combination of foci, it is expedient to consider them in pairs since this provides a way of identifying only the combination bases that are unique to these foci. The parasitic systems of flukes, the parasitocenoses of co-acting parasitic systems of "twin types", the structure of foci, the species-specific composition of ecosystems, and the ecological relations of the Opisthorchis fluke hosts act as the biotic bases of a combination of foci of Trematoda infections. By coinciding, the multihost hemipopulations of parasites and the susceptibility of host populations predetermine the combination of Opisthorchis fluke foci. The susceptibility of hosts, the multihost pattern of Opisthorchis flukes, the identity of parasitic systems, and the common mechanism of pathogen transmission act as the epizootic bases of a combination of invasion foci. The morphological structure and hydrological regime of a landscape act as the abiotic bases of a combination of foci. The hydrological regime is by its nature a universal mechanism of pathogen transmission. The foci of Opisthorchis flukes at the level of parasitocenosis of metacercarium populations and fish populations in the Konda River ecosystem are combined in the age groups of only carp (Cyprinidae) underyearlings and yearlings. The abiotic, biotic, and epizootic bases of a combination of natural foci of Opisthorchis flukes are, in the aggregate, the ecological bases of a combination of foci.

In the context of the present-day teaching of parasitocenoses and the proposition that the pathogen's population is the only compulsory and specific component of a natural focus, the author brings to light the ecological bases of the combination of natural foci of metorchiases, bilharziasis, opisthorchiasis, and methorchiasis (M. xanthosomus). Two first foci are one-host population-combined and the latter focus is a two-host population-combined focus. While analyzing the combination of foci, it is expedient to consider in pairs since this provides a way of identifying the bases of the combination, which are unique to these foci, and determining the level, pattern, type, and degree of the combination of foci and, on their basis, the type of a combined focus. It is noted that in biohelminthiases, detection of even hemipopulations of parasites points to the presence of natural foci. The morphological structure of the floodplain-river landscape of the Konda River acts as the abiotic basis of the combination of foci. The parasitic systems of flukes, the parasitocenoses of co-acting hemipopulations of the pathogens and populations of hosts, the structure of foci, the species-specific composition of ecosystems, and the ecological relations of Trematoda hosts act as the biotic bases of the combination of foci of Trematoda infections. The host susceptibility to infection with Trematoda hemipopulations and the multihostality of B. polonica and M. xanthosomus act as the epizootic bases of the combination of foci. The abiotic, biotic, and epizootic bases of the combination are, in the aggregate, the ecological bases of the combination of natural foci of zoonoses.

The paper presents the results of a study of the infection rates of mollusks of the family Bythiniidae (Bithynia tentaculata, Opisthorchophorus troscheli) and fishes with the larval stages of Opisthorchidae in different districts of the Yaroslavl Region. A total of 3,708 mollusks from the water reservoirs of different types (small rivers, lakes, ponds, and canals) were examined in the Nekouzsky, Yaroslavsky, and Pereslavsky Districts of the Yaroslavl Region in 1989 to 1999. Opisthorchis cercarias were found in 7 of the 10 studied water reservoirs. The total rate of infection of mollusks with all types with Trematoda partenitas and cercarias in different water reservoirs averaged 18.5 +/- 3.5% for Bithynia tentaculata and 19.1 +/- 4.1% for Opisthorchophorus troscheli. Trematoda metacercarias of the family Opisthorchidae were revealed in roaches, ides, verkhovkas, silver breams, and chubs in four different water reservoirs (small rivers and a lake) of the region. Pseudamphistomum truncates, Opisthorchis felineus, and Metorchis xanthosomus were present among the metacercarias found. It is concluded that there may be sporadic cases of Opisthorchis infection in wild and domestic animals and humans in the Yaroslavl Region.

More than a decade ago, it was postulated that components derived from trematode parasites block receptors on the defence cells of their snail intermediate hosts, thus preventing host-cell activation and parasite elimination. This phenomenon has still not been investigated extensively. However, recent work concerning the molecular regulation of the molluscan defence response provides a new framework for studies that focus on an extension of this original concept - subversion of host cell signalling by trematode parasites. The hypothesis is that, to facilitate survival and replication in their intermediate hosts, trematode parasites down regulate host defence responses by interfering with key signal-transduction pathways in snail defence cells.

The relationship of the annual trends in the infection of crucians (Carassius carassius) (L.) with Opisthorchis felineus metacercariae, in that of verkhovkas (Leucasplius delineatus) (Hackel), and in that of lake minnows (Phoxinus percnurus) (L.) with O. felineus and Metorchis billis to the environmental factors under natural fluctuations of the level of water and under the man-made effects on the water regime of the reservoir was studied. When the level of water naturally changes, the infection of crucians with Metorchis was found to be affected by their size, water temperature, and environmental pH values, and the human Opisthorchis affliction depends on the severity of infection of commercial-sized crucians by metacercariae. The infestation of the verkhovka was determined by the temperature of water and that of the lake minnow was by its size and the increased areas of the lake with the depths salubrious to its existence. With man-made effects (dewatering for watering agricultural lands) on the water regime of the reservoir, the infestation of the lake minnow depended on its size in the shallow water and on the level of water. Environmental factors, such as pH values, the area of shallow waters, and the size of mollusks, positively affected the higher extensiveness of infestation of mollusks with the parthenitae of opisthorchid flukes.

In an earlier study it was shown that Cryptocotyle lingua cercariae, matured in Littorina littorea from a polluted marine lagoon, displayed slower horizontal swimming rates, and reduced longevity compared to cercariae released by periwinkles from a cleaner environment. This work investigated whether the pollution-induced reduction in swimming rates was due to an inefficient swimming action or the adoption of a less direct swimming path. In addition, cercariae from L. littorea that had been transferred from an 'unpolluted' to a 'polluted' site for 1 month provided information on the speed with which pollutants affect cercariae through their intermediate hosts. Results indicated that, in general, horizontal swimming rates were reduced due to slower swimming rather than disorientation and longer swimming pathways. Effects of host transplantation to a polluted site were clearly evident after 1 month. Evidence suggested that the pollutants accumulated by the cercariae via their first intermediate host affected the neuromusculature associated with swimming performance rather than sensory structures. Bearing in mind the reduced viability of C. lingua cercariae in polluted sites it is assumed that high prevalence of this digenean in gastropods (at such sites) must be due to their continual introduction by infected birds attracted to these habitats from other areas.

Brackish-water mollusks inhabiting the mangrove areas along the Gulf of Thailand of Surat Thani Province were investigated for distribution, abundance and natural infections. Nine families and 32 species of brackish-water snails were recovered from 14 sampling stations. Species belonging to the genus Ceritidea of the family Potamididae were mainly examined and Cerithidea (Cerithideopsilla) Cingulata, C. (C.) djadjariensis, and C. (Cerithidea) charbonnieri were naturally infected with 2 types of trematode cercariae, and one which was undetermined. C. (C.) cingulata had the highest infection rate (38.5%). Viewing two snail communities, the first community on the mainland and the second on Samui Island in Surat Thani Province, 28 brackish-water mollusk species were present on the mainland, 15 species were evident on Samui Island, and 11 snail species were common to both the mainland and Samui Island. Measurement of community similarity based on species presence revealed an index of similarity of 0.51. Concerning land use by the local people in the station areas investigated, brackish-water snails in Surat Thani Province are facing habitat degradation by human use.

There are four species of 'pygmaeus' microphallids, namely Microphallus pygmaeus, M. piriformes, M. pseudopygmaeus and M. triangulatus (Trematoda: Microphallidae) which are parasites of marine birds and their sporocysts give rise to transmissible metacercariae inside littoral gastropods (mostly littorines). Universally primed polymerase chain reaction (UP-PCR) showed no apparent pattern between genetic diversity of the metacercariae as estimated by genomic banding profiles and their geographic region or molluscan host species. At the same time UP-PCR product cross-hybridization showed that M. pseudopygmaeus and M. triangulatus are genetically very similar, indicating that these taxa represent one species complex. In contrast, M. pygmaeus and M. piriformes are genetically well separated from each other and also from the pseudopygmaeus-triangulatus complex. Scanning electron microscopy of ventral spines, and analyses of spine angles and the number of teeth per spine, showed that all species differed significantly from one another. It was concluded that M. piriformes represents the original western member of the 'pygmaeus' group. Microphallus pygmaeus probably diverged from M. piriformes as it progressively specialized for sea duck final hosts. Microphallus pseudopygmaeus and M. triangulatus diverged from each other and the piriformes-pygmaeus ancestral line relatively recently. Microphallus pseudopygmaeus specialized for adoption of a wide range of gastropod host species and M. triangulatus developed morpho-functional specialization associated with final host exploitation.

The influence of the trematode invasion on the accumulation of heavy metals (Cu, Zn, Cd, Pb) by various organs of the mollusc Colletopterum ponderosum have been investigated. An increase of the coefficients of accumulation and bottom biological accumulation, and also changes in the accumulation in pairs of heavy metals were noted in the infected molluscs.

The effect of invasion of two trematode species, Bunocotyle progenetica (Hemiuridae: Bunocotylinae) and Cryptocotyle cancavum (Heterophiidae) on the host vitality is estimated. The mortality of infected and uninfected individuals of Hydrobia ulvae after different exposure time (3, 6, 9 and 12 hours) under extremely high temperature (+42 degrees C) was compared. The total death of the host was observed after 12 hours of experiment. The death rate of molluscs infected with B. progenetica ranged from 60 to 100% and was significantly higher (p < 0.01) than mortality of individuals infected with C. cancavum and uninfected snails in each case of exposure (3, 6 and 9 hours). At the same time the mortality of individuals infected with C. cancavum was significantly higher (p < 0.05) than the mortality of uninfected snails only after 9 hours of exposure (13.3 and 3.1%, respectively). Difference in pathogen effects B. progenetica and C. cancavum is expressed in different temperature resistance of the host that may be explained by different localisation of redia, their motile activity and manner of feeding. Besides, the invasion by C. cancavum causes the sterilization and accelerated growth of hosts. Low decreasing of the resistance to overheating in snails infected with this trematode could be explained by a compensation effect of this infection. This compensation realizes due to the redistribution of some part of the reproductive energy after the sterilization. An absence of parasitic castration in the case of infection with B. progenetica is a key reason of such considerable declining of their vitality. High lethality of the host appears to be adaptive for the parasite with the monoxenous life cycle.

Effect of trematod infection and different concentrations of detergent (20, 50, 80 mg/dm3) onto physical and chemical characteristics of haemolymph of Planorbarius corneus (content of Hb, density, active reaction, amount of Hb per unit of total mass and soft mass of the body) have been investigated. It was noted that all changes of named characteristics caused by detergent were more pronounced in infected mollusks.

This investigation quantifies some aspects of the parasite-host relationship between the digenean Microphallus piriformes and its intermediate host Littorina saxatilis, the rough periwinkle. M. piriformes has an abridged life-cycle with no free-living stages, metacercariae remain within host viscera. Noticeable differences in shell shape of parasitized and uninfected periwinkles were investigated. These differences in shell shape were defined by growth parameters of height, diameter and beta angle. The relationship between these parameters was examined together with their impact on parasite reproduction. All 3 shape parameters were altered in periwinkles infected by M. piriformes. The alteration in beta angle and height increased the available volume for parasites in the shell spire by about 12%. As metacercarial production per sporocyst has been shown to depend on host size, the increased volume enables considerable additional life-time reproduction by the parasite, of approximately 550-850 additional metacercariae in hosts of the usual size range. The form of gigantism found in this study is discussed in relation to previous concepts. It is suggested that gigantism in permanently castrated hosts is adaptive parasite manipulation of host physiology, favoured in parasites with abbreviated life-cycles, when host viability increases parasite transmission, and when an initially small host individual is infected.

The trematode Curtuteria australis uses the whelk Cominella glandiformis as first intermediate host and the cockle Austrovenus stutchburyi as second intermediate host before maturing in shorebirds. The whelk also happen to be an important predator of cockles on intertidal mudflats. In this study we show that whelks can act as temporary paratenic hosts for the trematode. A single whelk feeding on 1 cockle can ingest large numbers of metacercariae, which remain within the whelk for 1-3 days before passing out in feces. The viability of these metacercariae assessed as the percentage capable of successfully excysting under conditions simulating those inside a bird's digestive tract, is lower after passage through a whelk (48%) than before (59%). Still, given that shorebird definitive hosts prey on whelks as well as cockles, survival inside the whelk allows C. australis to complete its life cycle: overall, though, whelk predation is likely to be an important sink for the trematode population. To our knowledge, this is the first report of a trematode using a snail as both first intermediate host and paratenic host, offering an alternative transmission route for the parasite as a result of the unusual trophic relationships of its hosts.

12 rocky shore populations of Littorina saxatilis from three islands of Chupa Inlet (Kandalaksha Bay, White Sea) were examined for infection with trematodes. Morphometric characters (6 indexes of the shell and aperture shape) of molluscs were investigated for all these populations. Exposed and sheltered sites were considered at every island and high and low littoral samples were fulfilled at every site. Seven species of trematodes, Podocotyle atomon, Cryptocotyle lingua, Renicola sp., Himasthla sp., Microphallus piriformes, M. pygmaeus, M. pseudopygmaeus, were found. Uneven distribution of trematodes was confirmed by log-linear analysis. Sheltered populations of L. saxatilis have the greater infection prevalence than exposed ones. This is due to the heavy infection with M. piriformes and M. pygmaeus. The prevalences by these trematodes are up to 52.97% and 27.16% respectively in sheltered populations of the host. The prevalence of M. piriformes tend to be higher at the upper shore level of sheltered sites. In a contrast, the prevalence of M. pygmaeus is significantly higher at the low part of such sites. Factor analysis shows a significant association of the indices of L. saxatilis shell shape with three factors. The first one is associated with the "elongation" of a shell and reveals L. saxatilis from the exposed rocky shore to be more elongated than the molluscs from sheltered sites. The second one is connected with the "aperture shape" index. There is an association of this factor with the shore level position of samples. The third factor reflects the affect of trematodes on the shell shape. The molluscs infected with M. piriformes show "elongated" shell shape and relatively smaller aperture. Shall peculiarities of the hosts infected with M. piriformes and M. pygmaeus are somewhat different. The results of the factor analysis is justified by the series of analysis of variances on the values of shell indices (MANOVA) according to the factors "exposure", "shore level" and "infection".

The increased occurrence of pollutants in ecosystems is a continuing area of concern. It is known that numerous diseases of wild aquatic animals can occur with decreased or increased prevalences in areas associated with high or chronic levels of pollution. This may have serious implications for environmental health. There has consequently been an increasing number of laboratory and field studies on disease transmission under polluted conditions, especially focusing on digeneans of medical or economic importance. The effect of pollutants to the transmission of larval digeneans (miracidia, cercariae, metacercariae) and snail-digenean interactions is therefore considered. An overview and interpretation of the published literature on laboratory and field studies is provided. It is apparent from these studies that the influence of pollutants on digenean transmission is highly complex with much of the observed effects in the laboratory often masked by a complexity of other factors in the field. Future studies would benefit from a standardisation of experimental procedures, increasing the number of combined laboratory and field studies, and increasing the complexity of the experiments undertaken.

The release of Maritrema subdolum cercariae (Digenea: Microphallidae) from the marine mud snail Hydrobia ulvae is significantly affected by temperature, salinity, light and exudates from the second intermediate amphipod host. Based on (i) previously published data on temperature-salinity dependent H. ulvae activity, (ii) new experimental data on H. ulvae activity in light and darkness as well as in the presence and absence of host exudates, and (iii) the cercarial emergence rate from free moving snails and snails prevented from crawling, the present analysis indicates that emergence of M. subdolum larvae is regulated mainly by host activity as the ultimate factor for release. The adaptive significance of such an emergence strategy is emphasized.

The effects of environmental factors and exudates from the amphipod Corophium volutator on the emergence of Maritrema subdolum cercariae (Digenea: Microphallidae) from the snail Hydrobia ulvae were investigated in the laboratory. Increasing the temperature (15 to 25 degrees C) caused an overall 11-fold increase in emergence rate under varying salinities (24 to 36 per thousand). The effect of salinity depended on the experimental temperature. Emergence increased with increasing salinity at higher temperatures, but decreased with increasing salinity at 15 degrees C. Whereas the different levels of salinity had no effect, increasing the temperature significantly reduced the life span of cercariae. In comparison with complete darkness, light caused a two-fold increase in emergence, whereas an increment of the water pressure from 1.0 to 1.3 ATM (corresponding to 0 and 3 m of depth) left the shedding rate unaffected. Unidentified exudates from the second intermediate host, C. volutator, significantly depressed the cercarial emergence rate. The main transmission window of M. subdolum seems to occur during low water in tidal pools where light levels are high and solar radiation rapidly elevates the water temperature, as well as salinity through evaporation. The consequence of such a transmission strategy is discussed in relation to the impact of M. subdolum on the population dynamics of the second intermediate host.

Acanthoparyphium tyosenense Yamaguti, 1939 (Digenea: Echinostomatidae), was originally reported as an avian intestinal parasite; here, its presence is reported in 10 humans in the Republic of Korea. The patients were 9 adults aged 35-66 yr (males and females) and a young girl aged 7 yr residing in 2 coastal villages in Puan-gun, Chollabuk-do. The worms were recovered after treatment with praziquantel and purgation with magnesium salts. A total of 158 specimens (1-107 specimens/individual) was collected, together with varying numbers of other intestinal flukes. The patients had eaten various kinds of brackish water mollusks caught in an estuary near their villages. Five bivalves and a gastropod species suspected as sources of human infection were collected and examined. Two bivalves (Mactra veneriformis and Solen grandis) and the gastropod (Neverita bicolor) were found to be infected with the metacercariae of A. tyosenense; adult flukes were confirmed after the experimental infection of chicks. The results show that A. tyosenense infects humans and that brackish water mollusks are the source of human infection.

Sychnocotyle kholo n. g., n. sp. (Aspidogastrea: Aspidogastridae) is described from the small intestine of the freshwater turtle Emydura macquarii (Pleurodira: Chelidae). The new genus is distinguished from other aspidogastrids by the possession of the following suite of characters: no cirrus-sac; no hermaphroditic duct; four rows of alveoli on the ventral disc but no prominent papillae; Laurer's canal opening to the exterior. Eggs hatched to cotylocidia within 37-41 days at 17-24 degrees C. The life-cycle is obligate two-host, involving a mollusc and a freshwater turtle. Juvenile forms, almost entirely single worm infections, were found in the molluscs Corbiculina sp. (Bivalvia: Corbiculidae) and Thiara balonnensis (Prosobranchia: Thiaridae). Sychnocotyle is most likely to have evolved in Australia after the separation of Gondwanaland from Laurasia 120- 100 mya.

Five species of trematodes: Metagonimus yokogawai, M. katsuradai, Centrocestus armatus, Nanophyetus salmincola schikhobalowi and Paragonimus westermani ichunensis which are able to infect man have been found to develop with the participation of mollusks of the Juga genus from the rivers of the Maritime Territory. Some epizootiological aspects of the infections caused by these trematodes are considered in the paper.

Cercariae and metacercariae of the acanthocolpid trematode, Stephanostomum cloacum (Srivastava, 1938) are described and illustrated, based on material collected from Chilka Lake, a brackish water lagoon. Natural infections with the cercariae were found in the snail, Nassarius orissaensis and with the metacercariae in the bivalve, Modiolus undulatus. Cercariae are distomate, ophthalmoxiphidiocercous, and possess a small stylet, simple tail, four pairs of penetration glands arranged in two groups and a large granular excretory bladder. Development of the cercaria into the metacercaria was followed in M. undulatus under laboratory conditions. Infections with adults of S. cloacum were identified in the fish Triacanthus biaculeatus, found in the lake.

Analysis of the age structure of parthenitae of trematodes of sympatric populations of L. obtusata and L. saxatilis was conducted in 1983 for 6 localities in Kandalaksha Bay of the White Sea. 10 species of trematodes were found. The main populational differences in the level of infection are caused by Microphallus piriformes. Species with secondary dispersion in the life cycle are characterized by the increase in the extent of infection in populations with age. In Microphallidae species of "pygmaeus" group the age structure of infection depends on the overage infection of populations: the increase in the parasitic press leads to the maximum turning towards the young part of the snail's population. The establishment of the age structure of infection is considered to be one of the regulation mechanisms in parasite--host relations on the populational level.

The effect of parthenites and larvae of trematodes on the contents of total sugar, glucose as well as on the variations in the activity of acid and alkaline phosphatases of the haemolymph of Lymnaea stagnalis, Planorbis corneus and Viviparus viviparus has been studied. The studies have revealed differences in the degree of effect of individual species of parasites on their hosts depending on their localisation, infection intensity and developmental stage.

The effect of solutions of phenol (100, 250, 400 mg/l), copper sulfate, carbophos and bazudine (0.01, 0.1, 1.0 mg/l) on physical and chemical properties of haemolymph of Lymnaea stagnalis (L.) and Planorbarius corneus (L.) infected with parthenitae of trematodes was studied. Haemolymph viscosity decreases and its active reaction shifts to weakly acid one. Haemolymph density decreases only in solutions of carbophos and bazudine. With heavy infection the concentration of haemoglobin in haemolymph of P. corneus does not change under the effect of phenol but the total volume of haemolymph reduces considerably.