The 1994 plague epidemic of India: Molecular diagnosis and characterization of Yersinia pestis isolates from Surat and Beed

PCR analysis of formalin-fixed human autopsy tissues, rodent tissues, fleas and bacterial isolates from pneumonic patients from the 1994 plague epidemic confirmed the presence of the f1 and pla genes of Yersinia pestis in these samples. Several Y. pestis isolates from the epidemic areas were studied in respect of their plasmid profile, expression of F1 antigen and ribotype pattern. All the three plasmids known to be associated with virulence were present in the Surat isolates of Y. pestis. Presence of the F1 antigen, clasically used for diagnosis of Y. pestis infection, was demonstrated by immunoblotting. All the Indian isolates from the 1994 epidemic showed an identical ribotype profile. This profile, however, was different from those of Y. pestis isolates tested from other regions of the world. Upon digestion with EcoRI and EcoRV, and probing with E. coli 16S and 23S rRNA genes, DNA from these Y. pestis isolates gave two distinct profiles which, taken together, suggest that the present Indian isolates represent a new ribotype. The presence of Y. pestis signature genes in 5 out of 7 fleas collected from rodents in the affected areas, and the occurrence of the same ribotype in the Y. pestis isolates from domestic rodents, sylvatic rodents and the patients are strongly indicative of a clonal origin of this Indian strain and an epidemiological linkage among wild rodents, domestic rats and humans in the epidemic area.