Defining endemic cholera at three levels of spatiotemporal resolution within Bangladesh

Abstract

Although much focus is placed on cholera epidemics, the greatest burden occurs in settings in which cholera is endemic, including areas of South Asia, Africa and now Haiti1,2. Dhaka, Bangladesh is a megacity that is hyper-endemic for cholera, and experiences two regular seasonal outbreaks of cholera each year3. Despite this, a detailed understanding of the diversity of Vibrio cholerae strains circulating in this setting, and their relationships to annual outbreaks, has not yet been obtained. Here we performed whole-genome sequencing of V. cholerae across several levels of focus and scale, at the maximum possible resolution. We analyzed bacterial isolates to define cholera dynamics at multiple levels, ranging from infection within individuals, to disease dynamics at the household level, to regional and intercontinental cholera transmission. Our analyses provide a genomic framework for understanding cholera diversity and transmission in an endemic setting.

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Fig. 1: Phylogeny and household network of V. cholerae seventh pandemic strains.
Fig. 2: Spatiotemporal dynamics of seventh pandemic strains.
Fig. 3: Pairwise comparisons of SNVs within and between households and longitudinal samples.
Fig. 4: Effect of time of sampling on genetic diversity within a household.
Fig. 5: Maximum likelihood phylogeny of global seventh pandemic strains.

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Acknowledgements

This research was supported in part by NIAID grants R01 AI106878 to E.T.R., F.Q., S.B.C., F.C., A.I.K., Y.A.B. and R.C.C., R01 AI103055 to J.B.H., F.Q. and R.C.L., U01 AI058935 to S.B.C., F.Q., E.T.R., R.C.L. and J.B.H., U01 AI077883 to E.T.R. and F.Q., the Fogarty International Center-NIH D43 grant TW005572 to M.I.U. and T.R.B., as well as K43 TW010362 to T.R.B. This work was supported by the Wellcome Trust (grant 098051) to N.R.T. M.J.D. is supported by a Wellcome Trust Sanger Institute PhD Studentship. R.C.C. was supported by the Robert Wood Johnson Foundation Harold Amos Medical Faculty Development Program (grant 72424). We thank A. J. Page, J. Keane and the sequencing teams at the Wellcome Trust Sanger Institute. This work was supported by the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) which is grateful to the Governments of Bangladesh, Canada, Sweden and the UK for providing core/unrestricted support.

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Contributions

F.Q., E.T.R., N.R.T., R.C.C., S.B.C., J.B.H. and R.C.L. designed the study. F.C. and A.I.K. provided patient care and management. F.C., A.I.K., M.I.U., A.P., Y.A.B., R.C.C., T.R.B., J.B.H. and R.C.L. performed the experiments. D.D., M.J.D. and A.M. analyzed the data. D.D. wrote the manuscript, with major contributions from N.R.T., M.J.D., E.T.R. and F.Q. All authors contributed to the editing of the manuscript.

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Correspondence to Daryl Domman or Nicholas R. Thomson.

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Integrated supplementary information

Supplementary Figure 1 Maximum likelihood phylogeny showing the relationships between Vibrio cholerae isolates.

Three isolates sampled in Dhaka, shown in green, do not belong to the 7th Pandemic El Tor (7PET) lineage. The location and date of isolation for each isolate are listed. V. metoecus and Vibrio sp. RC586 were used as outgroups for the phylogeny.

Supplementary Figure 2 Cholera incidence from icddr,b hospital in Dhaka, Bangladesh.

The diarrheal disease surveillance system at icddr,b enrolls every fiftieth individual for full analysis. The different panels discriminate between O1 serotypes and the O139 serogroup.

Supplementary Figure 3 Distribution of SNVs across households and individuals.

a, Pairwise comparison of SNVs shared across households ordered from least to greatest variation within a single household. b, Pairwise variation across individuals sampled more than once. c, Pairwise variability within technical replicates.

Supplementary Figure 4 Phylogenies of isolates sampled from individuals over the course of an infection.

Each panel depicts the relatedness of samples from the same individual. The scale is the number of SNVs per site.

Supplementary Figure 5 Loss of CTX bacteriophage within an individual.

The phylogenetic relatedness of the isolates from this individual is shown in the top diagram. The bottom panel shows the coverage of reads mapped to the CTXϕ region of the reference genome N16961 for samples from day 2 and day 4.

Supplementary Figure 6 Temporal signal within the 813 7PET genomes.

Regression of the year of isolation versus root-to-tip divergence derived from the maximum likelihood tree of the 7PET lineage in Fig. 3. The hypermutator strains (n = 11) described by Didelot et al.39 contribute the majority (11 of 13) of the outliers seen in the root-to-tip regression.

Supplementary Figure 7 Time-scaled phylogeny for the 7PET V. cholerae lineage.

The tips are colored according to the geographic origin of the isolates. The nodes are in the same order as in Fig. 5.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–7

Reporting Summary

Supplementary Table 1

Metadata associated with the 303 Vibrio cholerae isolates from this study

Supplementary Table 2

Accessions and metadata for the 813 Vibrio cholerae genomes used for the global phylogeny

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Domman, D., Chowdhury, F., Khan, A.I. et al. Defining endemic cholera at three levels of spatiotemporal resolution within Bangladesh. Nat Genet 50, 951–955 (2018). https://doi.org/10.1038/s41588-018-0150-8

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