Abstract
BackgroundCholera is endemic in Bangladesh, with outbreaks reported annually. Currently, the majority of epidemic cholera reported globally is El Tor biotype Vibrio cholerae isolates of the serogroup O1. However, in Bangladesh, outbreaks attributed to V. cholerae serogroup O139 isolates, which fall within the same phylogenetic lineage as the O1 serogroup isolates, were seen between 1992 and 1993 and in 2002 to 2005. Since then, V. cholerae serogroup O139 has only been sporadically isolated in Bangladesh and is now rarely isolated elsewhere.MethodsHere, we present case histories of four cholera patients infected with V. cholerae serogroup O139 in 2013 and 2014 in Bangladesh. We comprehensively typed these isolates using conventional approaches, as well as by whole genome sequencing. Phenotypic typing and PCR confirmed all four isolates belonging to the O139 serogroup.FindingsWhole genome sequencing revealed that three of the isolates were phylogenetically closely related to previously sequenced El Tor biotype, pandemic 7, toxigenic V. cholerae O139 isolates originating from Bangladesh and elsewhere. The fourth isolate was a non-toxigenic V. cholerae that, by conventional approaches, typed as O139 serogroup but was genetically divergent from previously sequenced pandemic 7 V. cholerae lineages belonging to the O139 or O1 serogroups.ConclusionThese results suggest that previously observed lineages of V. cholerae O139 persist in Bangladesh and can cause clinical disease and that a novel disease-causing non-toxigenic O139 isolate also occurs.
Highlights
During 1992–93, V. cholerae O139 was first recognized in Bangladesh, India and other countries in Southeast Asia as a causative agent of epidemic cholera [1,2,3]
In Bangladesh, outbreaks attributed to V. cholerae serogroup O139 isolates, which fall within the same phylogenetic lineage as the O1 serogroup isolates, were seen between 1992 and 1993 and in 2002 to 2005
Cholerae that, by conventional approaches, typed as O139 serogroup but was genetically divergent from previously sequenced pandemic 7 V. cholerae lineages belonging to the O139 or O1 serogroups. These results suggest that previously observed lineages of V. cholerae O139 persist in Bangladesh and can cause clinical disease and that a novel disease-causing non-toxigenic O139 isolate occurs
Summary
During 1992–93, V. cholerae O139 was first recognized in Bangladesh, India and other countries in Southeast Asia as a causative agent of epidemic cholera [1,2,3]. It is clear from these data that the isolates causing the current (seventh) pandemic of cholera form a highly related monophyletic lineage dominated by isolates of the El Tor biotype and of the O1 serogroup This phylogeny, based on whole genome sequence of clinical isolates, shows three overlapping global expansions of V. cholerae since the pandemic began, denoted wave I, II, and III. The aim of this study was to compare these new V. cholerae O139 isolates to existing O139 and O1 isolate sequence data to determine if these new cases were caused by new O139 variants, or the persistence of strains that belong to the known O139 lineage This will inform the management of future cholera epidemics. V. cholerae serogroup O139 has only been sporadically isolated in Bangladesh and is rarely isolated elsewhere
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