Whole-Genome Sequencing of Vibrio cholerae O1 El Tor Strains Isolated in Ukraine (2011) and Russia (2014)

The seventh pandemic of cholera in Europe revisited by microbial genomics

In 1970, the seventh pandemic of cholera (7 P) reached both Africa and Europe. Between 1970 and 2011, several European countries reported cholera outbreaks of a few to more than 2,000 cases. We report here a whole-genome analysis of 1,324 7 P V. cholerae El Tor (7 PET) isolates, including 172 from autochthonous sporadic or outbreak cholera cases occurring between 1970 and 2011 in Europe, providing insight into the spatial and temporal spread of this pathogen across Europe. In this work, we show that the 7 PET lineage was introduced at least eight times into two main regions: Eastern and Southern Europe. Greater recurrence of the disease was observed in Eastern Europe, where it persisted until 2011. It was introduced into this region from Southern Asia, often circulating regionally in the countries bordering the Black Sea, and in the Middle East before reaching Eastern Africa on several occasions. In Southern Europe, the disease was mostly seen in individual countries during the 1970s and was imported from North and West Africa, except in 1994, when cholera was imported into Albania and Italy from the Black Sea region. These results shed light on the geographic course of cholera during the seventh pandemic and highlight the role of humans in its global dissemination.

Revisiting the Global Epidemiology of Cholera in Conjuction With the Genomics of Vibrio cholerae

Toxigenic Vibrio cholerae is responsible for 1.4 to 4.3 million cases with about 21,000-143,000 deaths per year. Dominance of O1 and O139 serogroups, classical and El tor biotypes, alterations in CTX phages and the pathogenicity Islands are some of the major features of V. cholerae isolates that are responsible for cholera epidemics. Whole-genome sequencing (WGS) based analyses of single-nucleotide polymorphisms (SNPs) and other infrequent genetic variants provide a robust phylogenetic framework. Recent studies on the global transmission of pandemic V. cholerae O1 strains have shown the existence of eight different phyletic lineages. In these, the classical and El Tor biotype strains were separated as two distinctly evolved lineages. The frequency of SNP accumulation and the temporal and geographical distribution supports the perception that the seventh cholera pandemic (7CP) has spread from the Bay of Bengal region in three independent but overlapping waves. The 2010 Haitian outbreak shared a common ancestor with South-Asian wave-3 strains. In West Africa and East/Southern Africa, cholera epidemics are caused by single expanded lineage, which has been introduced several times since 1970. The Latin American epidemics that occurred in 1991 and 2010 were the result of introductions of two 7CP sublineages. Sublineages representing wave-3 have caused huge outbreaks in Haiti and Yemen. The Ogawa-Inaba serotype switchover in several cholera epidemics are believed to be due to the involvement of certain selection mechanism(s) rather than due to random events. V. cholerae O139 serogroup is phylogenetically related to the 7CP El Tor, and almost all these isolates belonged to the multilocus sequence type-69. Additional phenotypic and genotypic information have been generated to understand the pathogenicity of classical and El Tor vibrios. Presence of integrative conjugative elements (ICE) with antibiotic resistance gene cassettes, clustered regularly interspaced short palindromic repeats-associated protein system and ctxAB promoter based ToxRS expression of cholera toxin (CT) separates classical and El Tor biotypes. With the availability of WGS information, several important applications including, molecular typing, antimicrobial resistance, new diagnostics, and vaccination strategies could be generated.