Over the past decade, a significant increase in the circulation of infectious agents was observed. With the spread and emergence of epizootics, zoonoses, and epidemics, the risks of pandemics became more and more critical. Human and animal health has also been threatened by antimicrobial resistance, environmental pollution, and the development of multifactorial and chronic diseases. This highlighted the increasing globalization of health risks and the importance of the human–animal–ecosystem interface in the evolution and emergence of pathogens. A better knowledge of causes and consequences of certain human activities, lifestyles, and behaviors in ecosystems is crucial for a rigorous interpretation of disease dynamics and to drive public policies. As a global good, health security must be understood on a global scale and from a global and crosscutting perspective, integrating human health, animal health, plant health, ecosystems health, and biodiversity. In this study, we discuss how crucial it is to consider ecological, evolutionary, and environmental sciences in understanding the emergence and re-emergence of infectious diseases and in facing the challenges of antimicrobial resistance. We also discuss the application of the “One Health” concept to non-communicable chronic diseases linked to exposure to multiple stresses, including toxic stress, and new lifestyles. Finally, we draw up a list of barriers that need removing and the ambitions that we must nurture for the effective application of the “One Health” concept. We conclude that the success of this One Health concept now requires breaking down the interdisciplinary barriers that still separate human and veterinary medicine from ecological, evolutionary, and environmental sciences. The development of integrative approaches should be promoted by linking the study of factors underlying stress responses to their consequences on ecosystem functioning and evolution. This knowledge is required for the development of novel control strategies inspired by environmental mechanisms leading to desired equilibrium and dynamics in healthy ecosystems and must provide in the near future a framework for more integrated operational initiatives.

The main microbial diseases affecting marine cultured bivalves have been revised on the basis of the etiologic agents, pathogenesis and pathogenicity. Several recent bivalve-interaction models have been studied, including Pecten larvae-Vibrio pectinicida, brown ring disease, juvenile oyster disease, Pacific oyster nocardiosis and summer mortalities of oysters. In addition, the taxonomy and phylogeny of new potential bivalve pathogens and their virulence factors have been established. Facing the difficulty of identifying bacterial strains associated with molluscan diseases (mainly vibriosis), polyphasic approaches have been developed to correlate the phenotype and genotype of potential pathogens. By evaluating likely virulence mechanisms, developing biotests to screen virulent strains and characterising the genes implicated in pathogenesis, a new generation of diagnostic tools, based on potential virulence, will be developed. Acquisition of pertinent diagnostic tools will be of major benefit in disease management, health surveillance and monitoring will contribute to maintaining sustainable aquaculture industries. Résumé -Les maladies bactériennes chez les bivalves marins, synthèse des travaux récents : tendances et évolution.Les principales maladies bactériennes affectant les bivalves marins aquacoles ont été synthétisées en se basant sur trois aspects, la démarche étiologique, l'étude de la pathogenèse et le mode d'action du pathogène. Plusieurs modèles d'interactions chez les bivalves ont été récemment étudiés, tels que Pecten-Vibrio pectinicida, la maladie de l'anneau brun chez les palourdes japonaises, la maladie des juvéniles d'huîtres américaines, la Nocardiose et les mortalités estivales chez les huîtres du pacifique. Ainsi, la taxonomie et la phylogénie de ces nouveaux pathogènes ont pu être établis et des facteurs de virulence identifiés. Face à la difficulté d'identification des souches bactériennes associées aux maladies des mollusques (principalement des vibrioses), une approche polyphasique a été développée afin de corréler le phénotype et le génotype des pathogènes potentiels. Des bio-tests utilisant toute une nouvelle génération d'outils sont en cours de développement afin de cribler les souches virulentes, d'évaluer les mécanismes potentiels de virulence et de caractériser les gènes impliqués dans la pathogenèse. L'acquisition de ces outils diagnostics permettra de mieux contrôler l'état sanitaire des bivalves aquacoles et contribuera ainsi à maintenir toute une filière industrielle conchylicole performante. 478C. Paillard et al.: Aquat. Living Resour. 17, 477-498 (2004)

International audienceThe impact of diets upon the fatty acid composition of haemocyte polar lipids and consequently upon immune parameters has been tested in the oyster Crassostrea gigas and the clam Ruditapes philippinarum. Oysters and clams were fed each of three cultured algae: Chaetoceros calcitrans, which is rich in 20:5(n-3) and 20:4(n-6) and poor in 22:6(n-3) fatty acids; T-Iso (Isochrysis sp.), which is rich in 22:6(n-3) and deficient in 20:5(n-3) and 20:4(n-6); and Tetraselmis suecica, which is deficient in 22:6(n-3) and contains only small amounts of 20:5(n-3) and 20:4(n-6). Fatty acid composition of haemocyte polar lipids was greatly affected by the diet. Oysters and clams fed C. calcitrans maintained a higher proportion of 20:5(n-3) and 20:4(n-6) in their haemocyte polar lipids, while these polyunsaturated fatty acids decreased drastically for animals fed T-Iso. However, the T-Iso diet maintained 22:6(n-3) in haemocyte polar lipids of both species. Higher 20:5(n-3) and 20:4(n-6) contents in diets appeared to have a positive effect upon total haemocyte count, granulocyte percentage, phagocytic rate and oxidative activity of clam haemocytes. Similarly, a positive effect of 20:5(n-3) on oxidative activity of oyster haemocytes was observed but to a lesser extent than in clams. Interestingly, when oyster haemocytes are submitted to a stressful condition, a positive effect of a higher dietary 22:6(n-3) content on the phagocytic rate was noticed

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A flow cytometric method to measure the production of oxidative metabolism products was adapted for use with Crassostrea gigas hemocytes. The method is based upon the oxidation, by hydrogen peroxide (H2O2), of intracellular 2',7'-dichlorofluorescin (DCFH) to green-fluorescent dichlorofluorescein. Activation of the respiratory burst (RB) was tested using phorbol myristate acetate with no success. By contrast, activation by zymosan particles increased oxidation of DCFH in C. gigas hemocytes, mainly granulocytes, and optimization tests showed a good response with 20 zymosan particles per hemocyte. Anti-aggregant solution, used to prevent hemocytes from clumping during bleeding, inhibited the RB activity measured by DCFH oxidation. The flow cytometric method developed during this work was used to evaluate the DCFH oxidation-inhibiting capacity of four strains of vibrio bacteria, known or suspected to be pathogenic for bivalves.

A taxonomic characterization was carried out on strains of the bacteria that cause the brown ring disease of clams. On the basis of their phenotypic and genotypic characteristics, these strains can be considered to constitute a new taxonomic unit, distinct from other Ebrio species. The guanine-plus-cytosine content of the strains ranged between 42.9 and 45.5 mol% (43.2 mol% for the proposed type strain). DNA-DNA hybridization studies showed 100% intragroup relatedness, but levels of genetic relatedness to the reference strains of different Ebrio species tested ranged between 15 and 58%. The strains have all the properties characteristic of the genus vibrio and can be clearly differentiated from other species of this genus by their growth at 4°C and their negative responses for growth at 30°C and in 6% NaCl, arginine dehydrolase, lysine decarboxylase, ornithine decarboxylase, and Voges-Proskauer reaction. The name yibrio tapetis is proposed for the new species; strain B1090 (CECT 4600) is the type strain.Since 1980, the genus Vibrio has been subject to an extensive taxonomic revision, and 15 new species have been described (12,22). At present, the genus Vibrio includes more than 35 species, most of which are of aquatic origin. Some of them have been demonstrated to be pathogenic for aquatic animals, including fish (Vibrio anguillarum, V. alginolyticus, K damsela, K Jischeri, K ordalii, K salmonicida, V. splendidus, and I/: vulniJicus) and shellfish (V. haweyi, K pelagtus, K splendidus, and

Vibrio tapetis is the causative agent of brown ring disease (BRD), which affects a species of clam, Ruditapes philippinarum. After incubation with V. tapetis, hemocytes lose filopods and become rounded, indicating cytotoxic activity of the bacterium. To rapidly quantify this cytotoxicity, a flow-cytometry test was developed based on the capacity of V. tapetis to inhibit adhesion of clam hemocytes to plastic. Several bacteria:hemocyte ratios, the cytotoxicity of other Vibrio spp. pathogenic to bivalves, and that of various V. tapetis isolates were tested. Inhibition of adherence is detectable with as few as 5 bacteria per hemocyte. The greater cytotoxic activity of V. tapetis compared to that of V. splendidus and V. pectenicida suggests a specific pathogenicity of V. tapetis to R. philippinarum hemocytes. Although all V. tapetis isolates inhibited adhesion, significant variations in cytotoxicity among isolates was demonstrated. KEY WORDS: Cytotoxicity · Flow cytometry · Vibrio tapetis · Ruditapes philippinarum · Bivalve hemocytes · Pathogenicity Resale or republication not permitted without written consent of the publisherDis Aquat Org 57: [109][110][111][112][113][114][115][116] 2003 external defense factors, such as phagocytosis by hemocytes in the pallial fluid as well as the epithelium.However, mechanisms of interactions between Vibrio tapetis and clam hemocytes remain poorly understood. Measurement of cytotoxicity of V. tapetis against hemocytes could be a good indicator of the virulence properties of this bacterium. In the literature, 2 assays using bacteria-hemocyte interaction have already been described: one was direct and employed microscopic observation, the other was indirect and used a chemiluminescence assay. The first used a time-lapse video recording to determine the toxic effect of V. anguillarum and V. alginolyticus on mussel Mytilus edulis hemocytes (Lane & Birkbeck 1999). These 2 Vibrio species cause cell-rounding of the hemocytes. The most toxic bacterium, V. anguillarum, was able to induce rounding in 50% of the hemocytes at a ratio of only 1 bacterium per hemocyte. Differences in cellrounding percentages permitted quantification of cytotoxicity. The second method was used to examine the effects of V. pectenicida and of its cytoplasmic extract on the respiratory burst of Pecten maximus hemocytes , Lambert et al. 2001). This indirect method used chemiluminescence to quantify production of reactive oxygen intermediates (ROIs). V. pectenicida, and in particular the cytoplasm extract, were responsible for the inhibition of chemiluminescence activity in oyster and scallop hemocytes.To better understand the cellular effects of Vibrio tapetis toward hemocytes, the present study was designed first to develop a cytotoxicity test using flow cytometry, and second to compare the pathogenicity of different V. tapetis strains on clam and oyster hemocytes. MATERIALS AND METHODSBacteria. The bacteria used in this study were generally isolated from BRD-diseased clams and asymptomatic cockles at ...

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