[Ecological interactions among Yersinia in their common reservoir, the rodent]. / Interactions écologiques des Yersinia au sein de l'hôte réservoir commun, le rongeur.

Plague, due to Yersinia pestis, is still active in various foci in the Americas, in Africa and Asia, whereas it has been absent from Europe since the end of the 18th century, after having killed the two-thirds of the continent's inhabitants within four centuries. Various hypothesis have been proposed to attempt to explain the spontaneous "eradication" of plague from Europe, including the improvement of hygiene and habitat, changes in the rat population and cross-immunity induced by other infections, such as salmonellosis, leprosy and other yersiniosis. The only Yersinia currently isolated in Europe are the species genetically related to Y. pestis, Y. pseudotuberculosis and Y. enterocolitica, which are less virulent and mostly enteropathogenic. Y. pestis and Y. pseudotuberculosis have a DNA relatedness of 90%, whereas it is of only 60% with Y. enterocolitica. Y. pseudotuberculosis has been used as efficient vaccine against plague. Present world epidemiological data show that Y. enterocolitica is progressively replacing Y. pseudotuberculosis. Experimental infection by Y. enterocolitica, inducing a transitory and spontaneously cured infection in the immunocompetent host, only inducing opportunistic infections in the immunodeficient host, promotes efficient immunity against plague. Thus, it seems likely that the emergence of some variants of Yersinia, less virulent than Y. pestis, but able to induce a long-lasting protective immunity against plague, have contributed to its eradication by a silent enzootic infection among the wild reservoirs of rodents.

Immunoblot studies in the differential diagnosis of porcine brucellosis: an immunodominant 62 kDa protein is related to the mycobacterial 65 kDa heat shock protein (HSP-65).

Smooth Brucella spp. share certain lipopolysaccharide antigens with other bacteria, resulting in serological cross-reactions which can prevent the definitive diagnosis of brucellosis. To identify other antigens with serodiagnostic potential, immunoblot studies following sodium dodecyl sulphate-polyacrylamide gel electrophoresis were carried out. Sera from pigs experimentally infected with Brucella suis and naturally infected feral pigs, sera from pigs from a farm with a known history of Yersinia enterocolitica 0:9 infection, Brucella Complement Fixation Test (CFT) reactor pigs (aetiology unknown) and pigs from consistently Brucella CFT negative farms were examined. Although B. suis infected pigs recognized a total of nine B. melitensis antigens, individual pigs rarely recognized more than three antigens in the range. A 62 kDa antigen was recognized by the majority (73%) of the Brucella infected pigs, but only by 10 to 23% of pigs from the other groups. This antigen was shown to be the Brucella homologue of the ubiquitous 65 kDa heat shock protein (HSP-65) family by immunoblot studies with 14 monoclonal antibodies to the Mycobacterium leprae HSP-65. Only four of these monoclones (Y1.2, ML-30, D7C and IIIC8) identified the B. melitensis 62 kDa protein suggesting that unshared, potentially Brucella specific, regions exist. Sera from Y. enterocolitica 0:9 infected pigs, CFT reactor pigs (aetiology unknown), CFT negative pigs and hyperimmune pig serum raised to Y. enterocolitica 0:9 also recognized B. melitensis antigens, most notably a 17 kDa protein. This antigen appears to be a common cross-reactive protein.