Genetic Diversity of Vibrio cholerae О1 El Tor during Epidemic Complications in the Siberian and Far East Regions

Abstract

The epidemic of cholera in Siberia and the Russian Far East during the seventh pandemic was recorded as sporadic cases of introduction of the infection into the territory or severe local outbreaks associated with the infection’s importation in the 1970s and 1990s. The genetic diversity and relationship of 83 V. cholerae O1 El Tor strains isolated from the region with epidemic complications were studied on the basis of the multilocus analysis of the variable number tandem repeats at five loci: VcA, VcB, VcC, VcD, and VcG. The VcB locus was characterized by the maximum polymorphism in the sample of the studied strains, while the VcC locus displayed the minimum polymorphism. Cluster analysis revealed the differentiation of V. cholerae strains during epidemic complications into seven clusters depending on the structure of the pathogenic determinants (typical and atypical El Tor vibrios), as well as on the time and direction of the pathogen importation. In some outbreaks in the Far East in 1999, the heterogeneity of the etiological agent populations was shown (five genotypes were detected among the outbreak strains from Yuzhno-Sakhalinsk, and six genotypes were determined among the strains from Primorskii krai). At the same time, the predominant MLVA profiles and their single locus variants were identified. The absence of a strict connection between the territory and the genotypes of V. cholerae outbreak strains (one strain from Yuzhno-Sakhalinsk showed the identity of the allele profile with the isolates from Vladivostok), as well as no correspondence of the V. cholerae genotype to a specific infection focus, was shown. According to the data of the MLVA typing, the V. cholerae O1 El Tor strains isolated from the Siberian and Far Eastern regions (Russia) with epidemic complications were characterized by the heterogeneity of their genetic organization, which agrees with the period and direction of their importation to the territory. During sporadic outbreaks of cholera, the clonality of the etiological agent was revealed. Closely related subclones, the emergence of which could result from the presence of the causative agent in the environment or passaging through a susceptible organism, were identified.