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      Laboratory and molecular surveillance of paediatric typhoidal Salmonella in Nepal: Antimicrobial resistance and implications for vaccine policy

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          Abstract

          Background

          Children are substantially affected by enteric fever in most settings with a high burden of the disease, including Nepal. However pathogen population structure and transmission dynamics are poorly delineated in young children, the proposed target group for immunization programs. Here we present whole genome sequencing and antimicrobial susceptibility data on 198 S. Typhi and 66 S. Paratyphi A isolated from children aged 2 months to 15 years of age during blood culture surveillance at Patan Hospital, Nepal, 2008–2016.

          Principal findings

          S. Typhi was the dominant agent and comprised several distinct genotypes, dominated by 4.3.1 (H58). The heterogeneity of genotypes in children under five was reduced compared to data from 2005–2006, attributable to ongoing clonal expansion of H58. Most isolates (86%) were non-susceptible to fluoroquinolones, associated mainly with S. Typhi H58 lineage II and S. Paratyphi A harbouring mutations in the quinolone resistance-determining region (QRDR); non-susceptible strains from these groups accounted for 50% and 25% of all isolates. Multi-drug resistance (MDR) was rare (3.5% of S. Typhi, 0 S. Paratyphi A) and restricted to chromosomal insertions of resistance genes in H58 lineage I strains. Temporal analyses revealed a shift in dominance from H58 Lineage I to H58 Lineage II, with the latter being significantly more common after 2010. Comparison to global data sets showed the local S. Typhi and S. Paratyphi A strains had close genetic relatives in other South Asian countries, indicating regional strain circulation. Multiple imports from India of ciprofloxacin-resistant H58 lineage II strains were identified, but these were rare and showed no evidence of clonal replacement of local S. Typhi.

          Significance

          These data indicate that enteric fever in Nepal continues to be a major public health issue with ongoing inter- and intra-country transmission, and highlights the need for regional coordination of intervention strategies. The absence of a S. Paratyphi A vaccine is cause for concern, given its prevalence as a fluoroquinolone resistant enteric fever agent in this setting.

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          Most cited references27

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          Fast gapped-read alignment with Bowtie 2.

          As the rate of sequencing increases, greater throughput is demanded from read aligners. The full-text minute index is often used to make alignment very fast and memory-efficient, but the approach is ill-suited to finding longer, gapped alignments. Bowtie 2 combines the strengths of the full-text minute index with the flexibility and speed of hardware-accelerated dynamic programming algorithms to achieve a combination of high speed, sensitivity and accuracy.
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            Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18.

            Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis.
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              Microreact: visualizing and sharing data for genomic epidemiology and phylogeography

              Visualization is frequently used to aid our interpretation of complex datasets. Within microbial genomics, visualizing the relationships between multiple genomes as a tree provides a framework onto which associated data (geographical, temporal, phenotypic and epidemiological) are added to generate hypotheses and to explore the dynamics of the system under investigation. Selected static images are then used within publications to highlight the key findings to a wider audience. However, these images are a very inadequate way of exploring and interpreting the richness of the data. There is, therefore, a need for flexible, interactive software that presents the population genomic outputs and associated data in a user-friendly manner for a wide range of end users, from trained bioinformaticians to front-line epidemiologists and health workers. Here, we present Microreact, a web application for the easy visualization of datasets consisting of any combination of trees, geographical, temporal and associated metadata. Data files can be uploaded to Microreact directly via the web browser or by linking to their location (e.g. from Google Drive/Dropbox or via API), and an integrated visualization via trees, maps, timelines and tables provides interactive querying of the data. The visualization can be shared as a permanent web link among collaborators, or embedded within publications to enable readers to explore and download the data. Microreact can act as an end point for any tool or bioinformatic pipeline that ultimately generates a tree, and provides a simple, yet powerful, visualization method that will aid research and discovery and the open sharing of datasets.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administrationRole: ValidationRole: Writing – original draftRole: Writing – review & editing
                Role: Data curationRole: Formal analysisRole: MethodologyRole: ValidationRole: VisualizationRole: Writing – review & editing
                Role: Formal analysisRole: MethodologyRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Project administration
                Role: ConceptualizationRole: Methodology
                Role: Data curationRole: Project administrationRole: Writing – review & editing
                Role: Data curationRole: Project administrationRole: Supervision
                Role: Data curationRole: Project administrationRole: Writing – review & editing
                Role: Data curationRole: Project administration
                Role: Data curationRole: Project administration
                Role: Funding acquisitionRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: Funding acquisitionRole: MethodologyRole: SupervisionRole: ValidationRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Funding acquisitionRole: Project administrationRole: SupervisionRole: ValidationRole: Writing – original draftRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS Negl Trop Dis
                PLoS Negl Trop Dis
                plos
                plosntds
                PLoS Neglected Tropical Diseases
                Public Library of Science (San Francisco, CA USA )
                1935-2727
                1935-2735
                23 April 2018
                April 2018
                : 12
                : 4
                : e0006408
                Affiliations
                [1 ] Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, Oxford, United Kingdom
                [2 ] Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
                [3 ] Oxford University Clinical Research Unit-Patan Academy of Health Sciences, Patan, Nepal
                [4 ] University of Otago, Christchurch, New Zealand
                [5 ] Wellcome Trust Sanger Institute and the Department of Medicine, Cambridge University, Cambridge, United Kingdom
                Massachusetts General Hospital, UNITED STATES
                Author notes

                I have read the journal's policy and the authors of this manuscript have the following competing interests. AJP has previously conducted studies on behalf of Oxford University funded by vaccine manufacturers, but currently does not undertake industry funded clinical trials. AJP chairs the UK Department of Health’s (DH) Joint Committee on Vaccination and Immunisation (JCVI) and is a member of the World Health Organisation Strategic Group of Experts (SAGE); the views expressed in this manuscript do not necessarily reflect the views of JCVI, DH or SAGE. The other authors have no conflicts of interest.

                ‡ KEH and AJP are joint senior authors

                Author information
                http://orcid.org/0000-0002-1674-8801
                http://orcid.org/0000-0002-8887-3492
                http://orcid.org/0000-0003-3403-4746
                http://orcid.org/0000-0003-4366-6403
                http://orcid.org/0000-0002-9546-6406
                http://orcid.org/0000-0003-3949-2471
                Article
                PNTD-D-18-00081
                10.1371/journal.pntd.0006408
                5933809
                29684021
                c7396c83-0d02-4784-bf10-a3f83ce8e065
                © 2018 Britto et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 19 January 2018
                : 25 March 2018
                Page count
                Figures: 6, Tables: 2, Pages: 19
                Funding
                CDB is a Rhodes scholar, class of 2015 funded by the Rhodes trust. ZAD was supported by the Wellcome Trust of Great Britain (106158/Z/14/Z). SD was supported by a McKenzie Fellowship from the University of Melbourne. KEH was supported by the NHMRC of Australia (Fellowship #1061409). GD is supported by the NIHR Cambridge, BRC and the Wellcome trust. AJP is funded the NIHR Oxford, BRC and Wellcome trust. The authors also wish to acknowledge the Gates foundation, which support enteric fever studies conducted by our group in Nepal. The sequencing of isolates in this study was funded by the Wellcome Trust Strategic Award: “A strategic vision to drive the control of enteric fever through vaccination” Strategic Award (106158/Z/14/Z). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine and Health Sciences
                Infectious Diseases
                Bacterial Diseases
                Salmonella
                Salmonella Typhi
                Biology and Life Sciences
                Microbiology
                Medical Microbiology
                Microbial Pathogens
                Bacterial Pathogens
                Salmonella
                Salmonella Typhi
                Medicine and Health Sciences
                Pathology and Laboratory Medicine
                Pathogens
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                Bacterial Pathogens
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                Biology and Life Sciences
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                Custom metadata
                vor-update-to-uncorrected-proof
                2018-05-03
                All relevant data are within the paper and its Supporting Information files.

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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