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Quantitative real-time polymerase chain reaction (qPCR) is probably the most used method for gene expression quantification because of its high sensitivity and specificity. Nevertheless, this technology can undergo experimental errors and variations. Normalization of the results using a reference gene is therefore necessary to minimize these variations. As the study of immune genes in bivalve mollusks has increased in the last years, the establishment of adequate and stable reference genes for bivalves is strongly required. We analyzed the behavior of four putative reference genes: ribosomal RNA 18S, actin, elongation factor 1 − α and α-tubulin. The suitability of these four genes as internal control for qPCR was evaluated in mussel (Mytilus galloprovincialis) and clam (Ruditapes philippinarum) hemocytes after bacterial challenge. Four independent approaches (BestKeeper, GeNorm, NormFinder and DeltaCt ) were used to assess the suitable genes for stable expression. For these particular circumstances, the most stable gene in hemocytes was elongation factor 1 − α for mussels and α-tubulin for clams.
The factor structure of the Reynolds Child Depression Scale (RCDS; Reynolds, 1989), analyzed by confirmatory factor analysis and the scale's psychometric characteristics in a sample of 315 participants (140 boys and 175 girls) and a clinical sample of 62 participants (37 boys and 25 girls) between 10 and 12 years old, are presented. Two models are tested with confirmatory factor analysis: a one-factor model and a five-factor model. Both models show a good fit, but the one-factor model was chosen because it is the most parsimonious. The reliability coefficient ranged from .87 (at test) to .89 (at retest) in the community sample, and was .90 in the clinical sample (at test). Test-retest reliability was .66 in the community sample. Concurrent validity with other self-reports that measure depressive symptomatology was high, both in the community sample (.76) and the clinical sample (.71). There were no significant sex differences but there were differences due to age (school grade).
The psychometric characteristics of the Children's Depression Inventory, CDI (Kovacs, 1992) in a sample of 1705 participants (792 boys and 913 girls) and a clinical sample of 102 participants (42 boys and 60 girls) between 10 and 18 years old are presented. Reliability coefficients range, for both samples, from .82 (test) to .84 (retest) in the community sample, and .85 (test, clinical sample); test-retest reliability is .81 in the community sample. The mean scores are similar to other Spanish and English ones. Girls score higher than boys. The cut-off point that best differentiates between depressive and community participants is 19, with a sensitivity of 94.7%, a specificity of 95.6%, a positive predictive value of .90, and a negative predictive value of .98.
An histology and pathological survey on carpet-shell clam cultured in the
south of Galicia (NW Spain) (Ruditapes decussatus) was carried out for a two years period
(2000-2001). A temporal distribution of the potentially pathogenic agents
were determined by histological analysis. In addition, stocks of molluscs
reported to suffer mortalities during the studied period were also analyzed
and the pathogenic burden determined. Pathogens do not follow a temporal
pattern over studied period and no significant differences were detected nor
on the presence nor in prevalence of these pathogens among all the analysed
stocks. Therefore, no direct relationship can be established between
infection by any pathogen and mortality episodes.
The genus Perkinsus includes protistan parasites infecting marine molluscs throughout
the world, some of which are associated with mass mortalities. Life cycle
involves vegetative proliferation within the host, by which a cell named
trophozoite undergoes successive bipartitioning. Other stages have been
observed in vitro or in vivo, depending on the species: hypnospore, zoosporangium and
zoospore. Molecular taxonomy supports a close affinity between
dinoflagellates and Perkinsus spp. Six species of Perkinsus are currently considered valid:
P. marinus, P. olseni, P. qugwadi, P. chesapeaki, P. andrewsi and P. mediterraneus. Histology and, above all, incubation of host tissues in Ray's
fluid thioglycollate medium (RFTM) are classic diagnostic methods. In
addition, more sensitive and quicker molecular diagnostic techniques based
on either immunoassays or PCR have been developed for Perkinsus spp. Epizootiological
studies have shown a marked influence of water temperature and salinity on
P. marinus infection in oysters Crassostrea virginica, thus determining parasite geographical range and
temporal disease dynamics (seasonality). In vitro cultures have been established for
four Perkinsus spp. Immune response to infection varies depending on host and
involves phagocytosis or encapsulation of the parasite cells by host
haemocytes. A polypeptide is secreted by clam Tapes philippinarum haemocytes that could kill
the parasite. In vitro cultured P. marinus cells secrete proteases that are likely
involved in degradation of host tissues. P. marinus can suppress the toxic oxygen
radicals produced by host haemocytes. In addition to host death, sublethal
effects caused by Perkinsus spp. (reduction of fecundity, growth, and condition) may
have significant ecological and economic implications. Various strategies
have been assayed to mitigate the consequences of P. marinus epizootics on the oyster
industry: modifications of management/culture procedures, selective breeding
to obtain resistant oyster strains, and the use of triploid oysters and
allochthonous oyster species. Some chemotherapeutants have been proved to
inhibit or kill parasite cells in vitro.
Among mollusc pathogens, paramyxeans are an important group of protistan
parasites belonging to the genera Marteilia and Marteilioides. Marteilia refringens and M. sydneyi are of particular concern given
their potential impact on mollusc aquaculture world-wide. Aber disease and
QX disease are currently listed by the OIE, the World Organisation for
Animal Health. After more than thirty years of existence in the scientific
literature, these organisms still pose questions and research challenges to
investigators. This paper reviews current knowledge of the group and key
references. The review was focused on taxonomy, epidemiology, pathology and
potential control methods for these organisms in order to enhance
understanding of paramyxean infection issues in mollusc aquaculture.
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