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. 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.

The safety of drinking water is evaluated by the results obtained from faecal indicators during the stipulated controls fixed by the legislation. However, drinking-water related illness outbreaks are still occurring worldwide. The failures that lead to these outbreaks are relatively common and typically involve preceding heavy rain and inadequate disinfection processes. The role that classical faecal indicators have played in the protection of public health is reviewed and the turning points expected for the future explored. The legislation for protecting the quality of drinking water in Europe is under revision, and the planned modifications include an update of current indicators and methods as well as the introduction of Water Safety Plans (WSPs), in line with WHO recommendations. The principles of the WSP approach and the advances signified by the introduction of these preventive measures in the future improvement of dinking water quality are presented. The expected impact that climate change will have in the quality of drinking water is also critically evaluated.

The in vivo and in vitro pathogenic activities of whole cells and extracellular products of Vibrio alginolyticus for cultured gilt-head sea bream were evaluated. The 50% lethal doses ranged from 5.4 × 10 ⁴ to 1.0 × 10 ⁶ CFU/g of body weight. The strains examined had the ability to adhere to skin, gill, and intestinal mucus of sea bream and to cultured cells of a chinook salmon embryo cell line. In addition, the in vitro ability of V. alginolyticus to adhere to mucus and skin cells of sea bream was demonstrated by scanning electron microscopy. The biological activities of extracellular products of V. alginolyticus were hydrolytic activities; the products were able to degrade sea bream mucus. V. alginolyticus was cytotoxic for fish cell lines and lethal for sea bream. Moreover, the extracellular products could degrade sea bream tissues. However, experiments performed with the bath immersion inoculation technique demonstrated that V. alginolyticus should be considered a pathogen for sea bream only when the mucus layer is removed and the skin is damaged.

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 Vibrio 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 Vibrio 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 Vibrio tapetis is proposed for the new species; strain B1090 (CECT 4600) is the type strain.

Lymphocystis disease is a geographically widespread disease affecting more than 150 different species of marine and freshwater fish. The disease, provoked by the iridovirus lymphocystis disease virus (LCDV), is characterized by the appearance of papillomalike lesions on the skin of affected animals that usually self-resolve over time. Development of the disease is usually associated with several environmental factors and, more frequently, with stress conditions provoked by the intensive culture conditions present in fish farms. In gilthead sea bream ( Sparus aurata ), an economically important cultured fish species in the Mediterranean area, a distinct LCDV has been identified but not yet completely characterized. We have used direct sequencing of the virome of lymphocystis lesions from affected S. aurata fish to obtain the complete genome of a new LCDV-Sa species that is the largest vertebrate iridovirus sequenced to date. Importantly, this approach allowed us to assemble the full-length circular genome sequence of two previously unknown viruses belonging to the papillomaviruses and polyomaviruses, termed Sparus aurata papillomavirus 1 (SaPV1) and Sparus aurata polyomavirus 1 (SaPyV1), respectively. Epidemiological surveys showed that lymphocystis disease was frequently associated with the concurrent appearance of one or both of the new viruses. SaPV1 has unique characteristics, such as an intron within the L1 gene, and as the first member of the Papillomaviridae family described in fish, provides evidence for a more ancient origin of this family than previously thought. IMPORTANCE Lymphocystis disease affects marine and freshwater fish species worldwide. It is characterized by the appearance of papillomalike lesions on the skin that contain heavily enlarged cells (lymphocysts). The causative agent is the lymphocystis disease virus (LCDV), a large icosahedral virus of the family Iridoviridae . In the Mediterranean area, the gilthead sea bream ( Sparus aurata ), an important farmed fish, is frequently affected. Using next-generation sequencing, we have identified within S. aurata lymphocystis lesions the concurrent presence of an additional LCDV species (LCDV-Sa) as well as two novel viruses. These are members of polyomavirus and papillomavirus families, and here we report them to be frequently associated with the presence of lymphocysts in affected fish. Because papillomaviruses have not been described in fish before, these findings support a more ancient origin of this virus family than previously thought and evolutionary implications are discussed.