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Yersinia ruckeri yersiniosis is a common bacterial disease in rainbow trout farms. A vaccine developed in the 1980s, targeting Y. ruckeri biotype 1, provided very good vaccine protection until the early 2000s. However, a re-emergence of the disease was observed, reflecting vaccine failures in various countries, particularly in France. A new biotype of Y. ruckeri, called biotype 2, was then described, differing from biotype 1 in particular by the immobile nature of the bacterium. Analysis of 28 genes involved in flagellar synthesis and function revealed 3 mutations in the fliG, flhC and flgA genes of 6 strains of biotype 2 isolated in France, mutations never described in strains of this biotype isolated in other European countries or in the United States. The emergence of Y. ruckeri biotype 2 thus seems to be independent between the different countries studied. The bypasses implemented by the bacterium under vaccine pressure are therefore very diverse. This may give rise to fears of the emergence of a new biotype under the pressure of the currently used vaccine containing the 2 biotypes 1 and 2.

Bibliography :

Moreau E., Thomas T., Brevet M., Thorin C., Fournel C., Calvez S. 2019. Mutations involved in the emergence of Yersinia ruckeri biotype 2 in France. Transboundary and Emerging Diseases, 66(3):1387-1394 DOI: 10.1111/tbed.13175.