Epizootiological study of rickettsiosis of the Saint-Jacques scallop Pecten maximus

Rickettsia-like microorganisms were described in gill endothelial cells during mass mortalihes of Saint-Jacques scallops Pecten rnaxin~us in Saint-Brieuc Bay (North Brittany, France) during winter 1985-86. In order to evaluate the epizoobological significance of rickettsiosis of scallops, an analyt~cal and descriptive epizootiological study was undertaken. The study included the geographic distribution, incidence and severity of the disease for several northern European and French scallop populations. Since the center of French scallop production is in Saint-Brieuc Bay, epizootiological investigations were concentrated in this area. Dissemination appeared to be by horizontal transmission. The pathogenic significance of the rickettsia-like organism in mortalities of P. maximus is discussed.