Pathogenesis of Experimental Vibriosis in Larval American Oysters, Crassostrea virginica

Abstract

Larval oysters were experimentally infected with isolates of pure cultures of marine Vibrio sp. These animals were studied live, histologically, with the immunofluorescent test and with electron microscopy. All inoculated groups, but no control groups, demonstrated decreased growth and/or high mortality.One bacterial isolate attached preferentially to larval shell and destroyed mantle tissue as it grew along the internal surface of the shell. Phagocytes consumed invading bacterial cells but were ultimately overwhelmed by the infection.The second bacterial isolate caused velar damage in young larvae that remained active. In these larvae, the velar cells became detached or internally disorganized and lost their rectractor muscle insertions. In more advanced larvae, detachment of absorptive cells of the digestive gland was the earliest change observed and seemed to result from attachment of bacterial antigens to the cell surface. In both younger and more advanced larvae, food cycling and nutrient utilization were disrupted early in the disease process. The older larvae showed a general atrophy.Clinical signs such as mantle cell detachment could be detected early in the disease. Other clinical observations and the immunofluorescent test were also useful in the early diagnosis of vibriosis in larval oysters.Key words: vibriosis, larval oysters, Crassostrea virginica, histology, electron microscopy, ultrastructure, immunofluorescence, oyster hatcheryDes larves d'huîtres ont été infectées expérimentalement par des isolats de cultures pures de Vibrio sp. marins. Ces animaux furent étudiés en vie, histologiquement, à l'aide du test d'immunofluorescence et enfin au microscope électronique. Tous les groupes inoculés, mais non les groupes témoins, accusent un déclin de croissance et/ou une mortalité élevée.