Global warming can affect the world's biota and the functioning of ecosystems in many indirect ways. Recent evidence indicates that climate change can alter the geographical distribution of parasitic diseases, with potentially drastic consequences for their hosts. It is also possible that warmer conditions could promote the transmission of parasites and raise their local abundance. Here I have compiled experimental data on the effect of temperature on the emergence of infective stages (cercariae) of trematode parasites from their snail intermediate hosts. Temperature-mediated changes in cercarial output varied widely among trematode species, from small reductions to 200-fold increases in response to a 10 degrees C rise in temperature, with a geometric mean suggesting an almost 8-fold increase. Overall, the observed temperature-mediated increases in cercarial output are much more substantial than those expected from basic physiological processes, for which 2- to 3-fold increases are normally seen. Some of the most extreme increases in cercarial output may be artefacts of the methods used in the original studies; however, exclusion of these extreme values has little impact on the preceding conclusion. Across both species values and phylogenetically independent contrasts, neither the magnitude of the initial cercarial output nor the shell size of the snail host correlated with the relative increase in cercarial production mediated by rising temperature. In contrast, the latitude from which the snail-trematode association originated correlated negatively with temperature-mediated increases in cercarial production: within the 20 degrees to 55 degrees latitude range, trematodes from lower latitudes showed more pronounced temperature-driven increases in cercarial output than those from higher latitudes. These results suggest that the small increases in air and water temperature forecast by many climate models will not only influence the geographical distribution of some diseases, but may also promote the proliferation of their infective stages in many ecosystems.

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Global warming and temperature-mediated increases in cercarial emergence in trematode parasites.

Climate change effects on trematodiases, with emphasis on zoonotic fascioliasis and schistosomiasis.

Host-parasite evolution: general principles and avian models.

Current knowledge of animal and zoonotic helminthiases in which effects of climate change have been detected is reviewed. Climate variables are able to affect the prevalence, intensity and geographical distribution of helminths, directly influencing free-living larval stages and indirectly influencing mainly invertebrate, but also vertebrate, hosts. The impact of climate change appears to be more pronounced in trematodes, and is mainly shown by increased cercarial production and emergence associated with global warming. Fascioliasis, schistosomiasis (S. japonicum) and cercarial dermatitis caused by avian schistosomes have been the focus of study. Alveolar echinococcosis is currently the only cestode disease that climate change has been found to influence. Nematodiases, including heterakiasis, different trichostrongyliases and protostrongyliases, ancylostomiases and dirofilariases, are the helminth diseases most intensively analysed with regard to climate change. It may be concluded that helminth diseases should be listed among the infectious diseases with which special care should be taken because of climate change in the future, especially in temperate and colder northern latitudes and in areas of high altitude.

https://web.oie.int/boutique/extrait/14mascoma443457.pdf

Effects of climate change on animal and zoonotic helminthiases.

Schistosomes infect hundreds of millions of people in the developing world. Transmission of these parasites relies on a stem cell-driven, clonal expansion of larvae inside a molluscan intermediate host. How this novel asexual reproductive strategy relates to current models of stem cell maintenance and germline specification is unclear. Here, we demonstrate that this proliferative larval cell population (germinal cells) shares some molecular signatures with stem cells from diverse organisms, in particular neoblasts of planarians (free-living relatives of schistosomes). We identify two distinct germinal cell lineages that differ in their proliferation kinetics and expression of a nanos ortholog. We show that a vasa/PL10 homolog is required for proliferation and maintenance of both populations, whereas argonaute2 and a fibroblast growth factor receptor-encoding gene are required only for nanos-negative cells. Our results suggest that an ancient stem cell-based developmental program may have enabled the evolution of the complex life cycle of parasitic flatworms.

DOI: http://dx.doi.org/10.7554/eLife.00768.001

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Functional genomic characterization of neoblast-like stem cells in larval Schistosoma mansoni

The Biology and Evolution of Trematodes

Preface. Introduction. Acknowledgements. 1: Organization of parthenogenetic and hermaphroditic generations of trematodes. 1. Parthenogenetic generations and their larvae. 2. The hermaphroditic generation. 2: The trematode life cycle as a system of adaptations. 1. Adaptations of the first parthenogenetic generation. 2. Adaptations of daughter generations of parthenitae. 3. Hermaphroditic generation. 3: The main types of trematode life cycles. 1. Trixenous (three-host) life cycles. 2. Trixenous (three-host) life cycles with two endogenous ag-glomerations. 3. Dixenous (two-host) life cycles. 4. Homoxenous (one-host) life cycles. 5. Tetraxenous (four-host) life cycles. 4: Specific traits of populations formed by trematodes. 1. On the nature of trematode populations. 2. Host-parasite interactions and their manifestation on popula-tional level. 3. Phase analysis of trematode populations. 4. General notes. 5: The main trends in trematode evolution. 1. The main trends of morphological evolution of trematodes. 2. Ways of biological radiation of trematodes into different ecosystems. 6: Evolution of life cycles and phylogeny of trematodes. 1. Origin and evolution of trematode life cycles. 2. The main trends in evolution of trematode life cycles. 3. Possible approaches to establishing a natural classification of trematodes. References. Index.

The Biology and Evolution of Trematodes: An Essay on the Biology, Morphology, Life Cycles, Transmissions, and Evolution of Digenetic Trematodes

The somatic musculature in trematode hermaphroditic generation (cercariae, metacercariae and adult) is presumed to comprise uniform layers of circular, longitudinal and diagonal muscle fibers of the body wall, and internal dorsoventral muscle fibers. Meanwhile, specific data are few, and there has been no analysis taking the trunk axial differentiation and regionalization into account. Yet presence of the ventral sucker (= acetabulum) morphologically divides the digenean trunk into two regions: preacetabular and postacetabular. The functional differentiation of these two regions is already evident in the nervous system organization, and the goal of our research was to investigate the somatic musculature from the same point of view. Somatic musculature of ten trematode species was studied with use of fluorescent-labelled phalloidin and confocal microscopy. The body wall of examined species included three main muscle layers (of circular, longitudinal and diagonal fibers), and most of the species had them distinctly better developed in the preacetabuler region. In majority of the species several (up to seven) additional groups of muscle fibers were found within the body wall. Among them the anterioradial, posterioradial, anteriolateral muscle fibers, and U-shaped muscle sets were most abundant. These groups were located on the ventral surface, and associated with the ventral sucker. The additional internal musculature was quite diverse as well, and included up to twelve separate groups of muscle fibers or bundles in one species. The most dense additional bundles were found in the preacetabular region and were connected with the suckers. Previously unknown additional somatic musculature probably provides the diverse movements of the preacetabular region, ventral sucker, and oral sucker (or anterior organ). Several additional muscle groups of the body wall (anterioradial, posterioradial, anteriolateral fibers and U-shaped sets) are proposed to be included into the musculature ground pattern of trematode hermaphroditic generation. This pattern is thought to be determined by the primary trunk morphofunctional differentiation into the preacetabular and the postacetabular regions.

/pdf/somatic-musculature-in-trematode-hermaphroditic-generation-2euxuw0bvd.pdf

Somatic musculature in trematode hermaphroditic generation

Digenea usually use ventral sucker for sustainable attachment within intestine of their definitive vertebrate host. However, if the ventral sucker is absent or poorly developed, the means of attachment are unclear. We investigated attachment and locomotion in such digeneans: three species of the family Microphallidae (Microphallus piriformes, M. pygmaeus, and Levinseniella brachysoma) and two species of the family Heterophyidae (Cryptocotyle concava and C. lingua). Their tegumental spines and musculature were described with use of fluorescent actin staining, confocal microscopy, and scanning electron microscopy. Locomotion of living worms was observed and recorded. Wide serrated tegumental spines probably play the main role in attachment. Their firm contact with the host mucosa may be provided by the action of the ventral concavity-when the entire body or its part acts as a sucker. Dorsoventral muscle bundles act like radial musculature of the sucker generating negative pressure in the ventral concavity. The solid layer of longitudinal muscle fibers on the ventral body surface provides support for the bottom of the ventral concavity. In all microphallids, a U-shaped arrangement of body wall musculature (mostly originating from longitudinal fibers) outlines posterior part of the ventral concavity ridge. In all the studied species, tegumental spines, body wall musculature, and dorsoventral muscle bundles are better developed in the forebody which moves more actively than the hindbody.

https://link.springer.com/content/pdf/10.1007%2Fs00436-018-6085-2.pdf

Morphological framework for attachment and locomotion in several Digenea of the families Microphallidae and Heterophyidae

Analysis of each group of living organisms should start with the morphologic description of various stages of the life cycle. Of particular importance are the main trends of morphological evolution as they serve as a basis for the development of evolutionary concepts of the investigated groups. In this chapter modern data on the morphology and biology of life cycle stages of trematodes are briefly reviewed and the principal trends of the morphologic evolution of this group of parasitic platyhelminthes are traced.

Andrej A. Dobrovolskij

Papers

The Biology and Evolution of Trematodes

The Biology and Evolution of Trematodes: An Essay on the Biology, Morphology, Life Cycles, Transmissions, and Evolution of Digenetic Trematodes

Somatic musculature in trematode hermaphroditic generation

Morphological framework for attachment and locomotion in several Digenea of the families Microphallidae and Heterophyidae

Organization of Parthenogenetic and Hermaphroditic Generations of Trematodes