EN
Yersiniosis has been spreading around the world, and the classical symptoms of the disease are associated with serotype O1 of this bacterium. Y. ruckeri has been isolated from different fish species but the most susceptible to infection are salmonids, especially rainbow trout. Infected fish and asymptomatic carriers are the main source of the infection, spreading bacteria with feces. The pathogenesis mechanisms of yersiniosis are not well known as yet. Gills are regarded as the entry route of Y. ruckeri rods but the likelihood of the disease depends on the virulence of the given strain. Characteristic clinical signs of yersiniosis, such as haemorrhages around the oral cavity, are causes by extracellular products (ECPs) of Y. ruckeri. Haemorrhages are found in internal organs as well. Post mortem examination showed a dysfunction of the swim bladder which consisted in the presence of bloody effusion fluid in its cavity. Reduction of stress factors during the culture and transport of fish as well as the application of vaccines as an immunoprophylactic effectively prevent yersiniosis. A number of medicines have been applied in the therapy of yersiniosis. Sulphonamides and quinolones are among the most frequently used.