RECENT EMERGENCE OF NEW VARIANTS OF YERSINIA-PESTIS IN MADAGASCAR

Yersinia pestis, the causative agent of plague, has been responsible f ar at least three pandemics. During the last pandemic, which started i n Hong Kong in 1894, the microorganism colonized new, previously unsca thed geographical areas where it has become well established, The aim of this longitudinal study was to investigate the genetic stability of Y. pestis strains introduced into a new environment just under a cent ury ago and to follow the epidemiology of any new genetic variant dete cted, In the present study, 187 strains of Y. pestis isolated between 1939 and 1996 from different regions of Madagascar and responsible mai nly far human cases of bubonic and pneumonic plague were studied. Our principal genotyping method nas rRNA gene profiling (ribotyping), whic h has previously been shown to be an effective scheme for typing Y. pe stis strains of different geographical origins, We report that all stu died Y. pestis strains isolated in Madagascar before 1982 were of clas sical ribotype B, the ribotype attributed to the Y. pestis clone that spread around the world during the third pandemic, In 1982, 1983, and 1994, strains with new ribotypes, designated R, Q, and T, respectively , were isolated on the high-plateau region of the island, Analysis of other genotypic traits such as the NotI genomic restriction profiles a nd the EcoRV plasmid restriction profiles revealed that the new varian ts could also be distinguished by specific genomic and/or plasmid prof iles, A follow-up of these new variants indicated that strains of ribo types Q and R have become well established in their ecosystem and ha j e a tendency to spread to new geographical areas and supplant the orig inal classical strain.