Abstract
Background Vibrio cholerae O1 El Tor dominated the seventh cholera pandemic which occurred in the 1960s. For two decades, variants of V. cholerae O1 El Tor that produce classical cholera toxin have emerged and spread globally, replacing the prototypic El Tor biotype. This study aims to characterize V. cholerae O1 isolates from outbreaks in Thailand with special reference to genotypic variations over time.Methods/FindingsA total of 343 isolates of V. cholerae O1 from cholera outbreaks from 2007 to 2010 were investigated, and 99.4% were found to carry the classical cholera toxin B subunit (ctxB) and El Tor rstR genes. Pulsed-field gel electrophoresis (PFGE) differentiated the isolates into 10 distinct pulsotypes, clustered into two major groups, A and B, with an overall similarity of 88%. Ribotyping, multiple-locus variable-number tandem-repeat analysis (MLVA), and PCR to detect Vibrio seventh pandemic island II (VSP-II) related genes of randomly selected isolates from each pulsotype corresponded to the results obtained by PFGE. Epidemiological investigations revealed that MLVA type 2 was strongly associated with a cholera outbreak in northeastern Thailand in 2007, while MLVA type 7 dominated the outbreaks of the southern Gulf areas in 2009 and MLVA type 4 dominated the outbreaks of the central Gulf areas during 2009–2010. Only MLVA type 16 isolates were found in a Thai-Myanmar border area in 2010, whereas those of MLVA types 26, 39, and 41 predominated this border area in 2008. Type 39 then disappeared 1–2 years later as MLVA type 41 became prevalent. Type 41 was also found to infect an outbreak area.ConclusionsMLVA provided a high-throughput genetic typing tool for understanding the in-depth epidemiology of cholera outbreaks. Our epidemiological surveys suggest that some clones of V. cholerae O1 with similar but distinctive genetic traits circulate in outbreak sites, while others disappear over time.
Highlights
The bacterium Vibrio cholerae causes cholera, an acute infectious diarrheal disease that can result in death without appropriate treatment
Our epidemiological surveys suggest that some clones of V. cholerae O1 with similar but distinctive genetic traits circulate in outbreak sites, while others disappear over time
Polymyxin B sensitivity, VP testing and PCR analysis for the rtxC gene indicated that all isolates were biotype El Tor, and the hexaplex PCR assay revealed that they contained a set of virulence genes and were positive for the El Tor-specific tcpA gene; one isolate did not carry rstR, ctxA, cholera toxin B subunit (ctxB), ace, and zot genes
Summary
The bacterium Vibrio cholerae causes cholera, an acute infectious diarrheal disease that can result in death without appropriate treatment. In Bangladesh, all El Tor isolates of V. cholerae O1 obtained since 2001 have produced classical cholera toxin [6]. The World Health Organization reported that V. cholerae El Tor variant strains cause more severe episodes of cholera with higher fatality rates, compared with prototypic El Tor strains [15]. Due to these aspects of clinical manifestation and altered characteristics of cholera agents in recent years, more detailed investigations of cholera are required. Variants of V. cholerae O1 El Tor that produce classical cholera toxin have emerged and spread globally, replacing the prototypic El Tor biotype. This study aims to characterize V. cholerae O1 isolates from outbreaks in Thailand with special reference to genotypic variations over time
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