Parassitologia最新文献

Host-parasite cophylogeny is a topic that has grasped the attention of scientists since the end of the 19th century, but the development of dedicated analytical methods only arose in the last 30 years. Research on host-parasite systems and on the development of more and more sophisticated numerical methods to estimate the degree of cospeciation has thus progressed, permitting the elaboration of evolutionary scenarios. The main outcome of these studies is that the expected clear pattern of cospeciation between many hosts and parasites is often obscure. In practice, much attention has been devoted to few host-parasite systems. Particularly, aquatic host-parasite associations have not been so extensively studied, and, after briefly reviewing the main analytical methods, this paper focuses on host-monogenean systems, because this kind of interaction is expected to be an ideal model for cophylogeny studies. But is it? And what does it tell us about the evolutionary and ecological forces driving cospeciation in the open sea? Biogeography should also be considered when possible, and it has been useful for explaining some patterns of cospeciation. It should thus be more deeply exploited in the future. We need new methods and new biological models that better, if not fully, depict patterns and thereby permit deeper understanding of processes within cophylogenetic patterns.

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.

In recent years there has been an increasing number of papers showing how parasitism and pollution can interact with each other in aquatic organisms. Apart from parasitological aspects these interactions are also important in terms of ecotoxicological research. The current presentation aims at identifying three promising directions for future research in the interdisciplinary field of parasitology and ecotoxicology. 1. Parasites as sinks for pollutants within their hosts: Some parasites are able to reduce pollutant levels in the tissues of their host. The reduction of pollutants is an interesting implication since parasites are beneficial to their hosts from this perspective. In other cases free-living accumulation indicators may erroneously indicate low levels of pollution if they are infected with parasites. 2. Parasites as a diagnostic tool to test bioavailability of substances. In order to take up and accumulate pollutants the substances have to be metabolized by the host first. Accordingly, the detection of substances within endoparasites is a sign for the biological availability of pollutants. 3. Changes of biomarker responses of the host against pollutants. Parasites can alter physiological reactions of their hosts against pollutants in different ways. Therefore, in ecotoxicological studies, examining the question whether exposure to certain chemicals affects the physiological homeostasis of a test organism, it is important to use organisms that are known to be uninfected.

More than 40 species of marine fishes are cultured in China and a wide variety of parasites are reported as lethal pathogens of these fishes in culture conditions. In the case of net cages, the culture facilities provides a good substrate for monogenean eggs to become entangled and the intensive aggregation of fishes facilitates the transmission of parasites between hosts. Relatively thorough studies on parasitic pathogens of marine fishes in China predominately concern the ciliate Cryptocaryon irritans and capsalid monogeneans (mainly Benedenia sp. and Neobenedenia sp.). Although nearly all such reports are related to treatment procedures, no single method has proved to be adequate for the effective control of these parasitic pathogens in marine cultured fishes. The National Fisheries Technology Extension Center (NFTEC) has established surveillance systems to monitor the diseases of aquaculture, including the parasitic diseases of maricultured fishes. The national monitoring stations for diseases of cultured marine fishes are distributed in the coastal counties or cities and provide remote in situ diagnoses of diseased fishes. International cooperation and effort are required for the control of parasitic diseases of marine finfish because of both the increasing international trade of eggs (seed) and larvae and commercial products in terms of live marine finfishes, which can readily result in the transmission of pathogens.

Recent studies have demonstrated the invalidity of the Pseudophyllidea, a long-term recognised order of tapeworms (Platyhelminthes: Cestoda), typical in possessing two dorsoventrally situated attachment organs called bothria. In fact, cestodes parasitic in tetrapods, especially mammals including man, form a relatively basal group called provisionally the "Diphyllobothriidea", whereas tapeworms occurring in freshwater and marine fish, with a few taxa known from amphibians (frogs and newts), belong to a more derived clade, for which the name "Bothriocephalidea" is tentatively proposed. Revision of the "Bothriocephalidea", based on literary data, study of type- and voucher specimens and extensive newly collected material made it possible to critically review the species composition of the group and to prepare a tentative list of its valid species. Out of 305 nominal taxa, only 125 species are considered to be valid. In addition, the spectrum of definitive hosts and geographical distribution of bothriocephalideans are briefly discussed.

Parasite communities in fish hosts are not uniform in space: their diversity, composition and abundance vary across the geographical range of a host species. Increasingly urgently, we need to understand the geographic component of parasite communities to better predict how they will respond to global climate change. Patterns of geographical variation in the abundance of parasite populations, and in the diversity and composition of parasite communities, are explored here, and the ways in which they may be affected by climate change are discussed. The time has come to transform fish parasite ecology from a mostly descriptive discipline into a predictive science, capable of integrating complex ecological data to generate forecasts about the future state of host-parasite systems.

Although nematodes (Nematoda) belong to the most frequent and the most important parasites of fishes in the freshwater, brackish-water and marine environments throughout the world, the present knowledge of these parasites remains still incomplete, especially as to their biology and ecology, but also taxonomy, phylogeny, zoogeography, and the like. However, a certain progress in the research of fish nematodes has been achieved during recent years. An overview of some of the most important discoveries and results obtained is presented. As an example, existing problems in the taxonomy of these nematodes are shown in the dracunculoid family Philometridae (presently including 109 species in 9 genera), where they are associated mainly with some biological peculiarities of these mostly important tissue parasites. Nematodes of the Dracunculoidea as a whole remain poorly known; for example, of 139 valid species parasitizing fishes, 81 (58%) are known by females only and the males have not yet been described for members of 8 (27%) of genera. A taxonomic revision of this nematode group, based on detailed morphological, life history and molecular studies of individual species, is quite necessary; for the time being, Moravec (2006) has proposed a new classification system of dracunculoids, where, based on previous molecular studies, the Anguillicolidae is no longer listed in Dracunculoidea, but in an independent superfamily Anguillicoloidea. Important results have recently been achieved also in the taxonomy of fish nematodes belonging to other superfamilies, as well as in studies of their geographical distribution and diversity in different parts of the world and those of their biology. Opportunities for more detailed studies of fish nematodes have recently greatly improved with the use of some new methods, in particular SEM and DNA studies. There is a need to create a new classification system of these parasites reflecting phylogenetic relationships; a prerequisite for this is taxonomic revisions of different groups based on detailed studies of individual species, including mainly their morphology, biology and genetics. Further progress should concern studies on various aspects of biology, ecology and host-parasite relationships, because these data may have practical implications.

There is no doubt that the aquatic environments receive large quantities of chemicals as consequence of human activities and that those substances have a detrimental effect on human health. Despite the obvious need for effective disposal of these substances, we need to understand and prevent the outcome of harmful environmental exposures. Thus, we need biomarkers and bioindicators to advance our understanding to these harmful exposures and their biological effects. In the last three decades a large number of publications has suggested that aquatic organisms and their parasites (mainly helminths and ciliate protozoans) are useful bioindicators of chemical pollution. However, the main weakness of this approach is that after exposure the population size of these parasites can increase or decrease without a consistent pattern. I suggest that this is in part due to the lack of focus on the correct spatial or temporal scales at which the environment is acting over our study object. Thus, I propose to use spatially explicit (= georeferenced) data for determining whether there is spatial structure in our study area. Spatial structure is the tendency of nearby samples to have attribute values more similar than those farther apart. These attributes are shaped by environmental variables acting at specific spatial and temporal scales. Thus, I suggest to consider these tools for determining the correct spatial or temporal scales of study, but also to record pollutant concentrations, bioindicators, biomarkers and parasites at individual host level. Combining this information with long-term monitoring programs is likely to improve our understanding of the effects of chemical pollutants over the aquatic environments.

The number of sibling species of anisakid nematodes detected over the last two decades has been increased, fuelled by the use of genetic/molecular methodologies. In the present review, we summarize the biological species discovered within most of the nominal species belonging to the genera Anisakis, Contracaecum and Pseudoterranova by the use of allozyme (20-24 loci studied) and recently confirmed by us using mitochondrial cox-2 gene sequence analysis (mtDNA cox-2). Ecological evidence relating to the distributional range of the genetically detected sibling species and their host preferences, which represent data sets that can be utilized for species delimitation and definition, are summarized.