Patterns and processes of larval emergence in an estuarine parasite system.
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Trematode parasites in intertidal estuaries experience constantly varying conditions, with the presence or absence of water potentially limiting larval transport between hosts. Given the short life spans (< or =24 h) of cercariae, emergence timing should be optimized to enhance the probability of successful transmission. In the present study, field measurements and laboratory experiments identified processes that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclusively during daylight hours, and only when snails were submerged. The three factors operate over different temporal scales: temperature monthly, light diurnally (24-h period), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hierarchy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually reproduced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on subsequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Duration of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emergence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. Together, exogenous and endogenous factors control emergence of trematode cercariae, mitigating the vagaries of an intertidal environment. (+info)
Range limits and parasite prevalence in a freshwater snail.
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Geographical range limits are thought to be set by species' physiological or ecological adaptation to abiotic factors, but the importance of biotic factors such as parasitism in determining range limits has not been well explored. In this study the prevalence of trematode parasitism in populations of a freshwater gastropod snail, Lymnaea stagnalis, increased sharply as this species approached its western UK range limit. The likelihood of trematode infection increased with snail size, but high prevalence at the range edge was not a result of interpopulation variation in snail size. Changes in population growth rates resulting from high rates of parasitism at the range edge could contribute to range limitation. The mechanism driving high rates of parasitism at the range edge is not clear, but changes in abiotic factors towards the range limit may influence snail life history and immune response to trematode infection, indirectly altering the prevalence of parasites in marginal host populations. (+info)
Hepatic lesions in cetaceans stranded in the Canary Islands.
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This article describes the gross, histopathologic, and ultrastructural findings of the livers of cetaceans stranded on the coast of the Canary Islands between 1992 and 2000. A total of 135 cetaceans were included in the study, among which 25 were common dolphins (Delphinus delphis), 23 Atlantic spotted dolphins (Stenella frontalis), 19 striped dolphins (Stenella coeruleoalba), and 15 other species of dolphins and whales. The most common lesion observed in these animals was a nonspecific chronic reactive hepatitis (47/135), followed by hyaline intracytoplasmic inclusions in hepatocytes (33/135). Parasitic cholangitis was detected in 8/135 animals, whereas hepatic lipidosis was presented in 7/135 animals. The ultrastructure of hyaline hepatocytic cytoplasmic inclusions is described, and possible causes of these inclusions are discussed. (+info)
Metazoan parasite species in cultured mussel Mytilus galloprovincialis in the Thermaikos Gulf (North Aegean Sea, Greece).
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This is the first study on parasites of cultured Mytilus galloprovincialis L. in Greek waters, and is based on samples collected every 2 to 3 mo between September 2000 and November 2001 at 3 stations in the Thermaikos Gulf. Each sample comprised 40 mussels. We found 4 metazoan parasite species: hydroid Eugymnanthea inquilina, gill turbellarian Urastoma cyprinae, trematode Proctoces maculatus and gut copepod Mytilicola intestinalis. Of 840 mussels examined, 406 (48.3%) mussels were harbouring hydroids of E. inquilina, 278 (33.1%) were infested with U. cyprinae, 94 (11.2%) were infested with M. intestinalis, and only 7 (0.8%) were infested with P. maculatus. The prevalence and intensity of these parasites were related to temperature and pollution. Mussels infested with these parasites had significantly lower condition indices than non-infested mussels; larger mussels were more often infested than smaller ones. (+info)
Parasitic infection of sole Solea solea by Prosorhynchus spp. metacercariae (Digenea, Bucephalidae) in Atlantic nurseries under mussel cultivation influence.
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Cysts of metacercariae were obtained on 2 dates from juvenile sole Solea solea sea-sampled in an area of mussel cultivation (Pertuis Charentais, Bay of Biscay, France). An initial assessment of parasite genus and infestation level was based on 192 cysts extracted from 2 fish samples, taken in August (n = 20) and December 2000 (n = 14). Our results confirmed the sole as second intermediate host of bucephalid trematodes of the genus Prosorhynchus, which has not previously been noticed in Atlantic stocks. Prevalence, ca. 65% on both dates, indicated an substantial infestation of these small fish, with a mean abundance of parasites increasing from August (3.3 +/- 1.1) to December (8.1 +/- 3.4). Cysts were localised in all body parts of the host, and positioning varied depending on sampling date. However, the cephalic area was always the most infested (72.7 and 49.1% in August and December, respectively). Parasite measurements suggested a protracted infestation process, which may be initiated in spring during sole settlement. Most of the largest metacercariae had the rhynchus characteristics of P. crucibulum, though the possibility of them being other species (P. squamatus, P. aculeatus) could not be excluded. As Mytilus edulis is the first intermediate host of Prosorhynchus spp., possible relationships between mussel culture and sole parasitosis are discussed. (+info)
Molecular phylogenic location of the Plagiorchis muris (Digenea, Plagiorchiidae) based on sequences of partial 28S D1 rDNA and mitochondrial cytochrome C oxidase subunit I.
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To determine the molecular phylogenic location of Plagiorchis muris, 28S D1 ribosomal DNA (rDNA) and mitochondrial cytochrome C oxidase subunit I (mtCOI) were sequenced and compared with other trematodes in the family Plagiorchiidae. The 28S D1 tree of P. muris was found to be closely related to those of P. elegans and other Plagiorchis species. And, the mtCOI tree also showed that P. muris is in a separate clade with genus Glypthelmins. These results support a phylogenic relationship between members of the Plagiorchiidae, as suggested by morphologic features. (+info)
Parasitic castration of Eurhomalea lenticularis (Bivalvia: Veneridae) by a digenetic trematode: quantitative histological analysis.
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The clam Eurhomalea lenticularis may be parasitized by digenean trematodes of the family Plagiorchidae, specifically in the gonads (parasitic castration). A quantitative histological analysis of the parasitized gonads demonstrated a significant decrease in gonadal area, in the size of individual acini, and in the numbers of differentiated germ cells compared to unparasitized clams. Castration may be caused by mechanical compression due to trematode sporocyst growth. However, the uniform loss of germ cells in areas without sporocysts suggests that a more generalized mechanism is responsible. We suggest that parasitic castration has a primary effect on the host's neuroendocrine and gametogenic systems that regulate gamete production. (+info)
Analysis of p51, groESL, and the major antigen P51 in various species of Neorickettsia, an obligatory intracellular bacterium that infects trematodes and mammals.
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The p51 gene that encodes the major antigenic 51-kDa protein in Neorickettsia risticii was identified in strains of Neorickettsia sennetsu and the Stellantchasmus falcatus agent but not in Neorickettsia helminthoeca, suggesting that p51-based diagnosis would be useful to distinguish among them. groESL sequencing results delineated the phylogenic relationships among Neorickettsia spp. (+info)