Large outbreak of clinical cholera due to Vibrio cholerae non-O1 in Bangladesh

Synthesis of the conjugation-ready β-mannosamine-containing O-antigen repeat from Vibrio cholerae O14

Chemical synthesis of the trisaccharide repeating unit of the O-antigen from Vibrio cholerae has been accomplished through a linear strategy. The reducing end 1,2-cis mannosamine unit has been achieved through the azide inversion of the 2-OH position of a suitably protected glucose moiety. The crucial (S)-3-hydroxybutyric acid is inserted successfully at the last stage through EDC-HOBt coupling. The target trisaccharide, in the form of its 2-aminoethyl glycoside, is ready for further conjugation.

Dynamics of efflux pumps in antimicrobial resistance, persistence, and community living of Vibrionaceae

The marine bacteria of the Vibrionaceae family are significant from the point of view of their role in the marine geochemical cycle, as well as symbionts and opportunistic pathogens of aquatic animals and humans. The well-known pathogens of this group, Vibrio cholerae, V. parahaemolyticus, and V. vulnificus, are responsible for significant morbidity and mortality associated with a range of infections from gastroenteritis to bacteremia acquired through the consumption of raw or undercooked seafood and exposure to seawater containing these pathogens. Although generally regarded as susceptible to commonly employed antibiotics, the antimicrobial resistance of Vibrio spp. has been on the rise in the last two decades, which has raised concern about future infections by these bacteria becoming increasingly challenging to treat. Diverse mechanisms of antimicrobial resistance have been discovered in pathogenic vibrios, the most important being the membrane efflux pumps, which contribute to antimicrobial resistance and their virulence, environmental fitness, and persistence through biofilm formation and quorum sensing. In this review, we discuss the evolution of antimicrobial resistance in pathogenic vibrios and some of the well-characterized efflux pumps' contributions to the physiology of antimicrobial resistance, host and environment survival, and their pathogenicity.

Genomic Characteristics of Recently Recognized Vibrio cholerae El Tor Lineages Associated with Cholera in Bangladesh, 1991 to 2017

Comparative genomic analysis of Vibrio cholerae El Tor associated with endemic cholera in Asia revealed two distinct lineages, one dominant in Bangladesh and the other in India. An in-depth whole-genome study of V. cholerae El Tor strains isolated during endemic cholera in Bangladesh (1991 to 2017) included reference genome sequence data obtained online. Core genome phylogeny established using single nucleotide polymorphisms (SNPs) showed V. cholerae El Tor strains comprised two lineages, BD-1 and BD-2, which, according to Bayesian phylodynamic analysis, originated from paraphyletic group BD-0 around 1981. BD-1 and BD-2 lineages overlapped temporally but were negatively associated as causative agents of cholera during 2004 to 2017. Genome-wide association study (GWAS) revealed 140 SNPs and 31 indels, resulting in gene alleles unique to BD-1 and BD-2. Regression analysis of root to tip distance and year of isolation indicated early BD-0 strains at the base, whereas BD-1 and BD-2 subsequently emerged and progressed by accumulating SNPs. Pangenome analysis provided evidence of gene acquisition by both BD-1 and BD-2, of which six crucial proteins of known function were predominant in BD-2. BD-1 and BD-2 diverged and have distinctively different genomic traits, namely, heterogeneity in VSP-2, VPI-1, mobile elements, toxin encoding elements, and total gene abundance. In addition, the observed phage-inducible chromosomal island-like element (PLE1), and SXT ICE elements (ICETET) in BD-2 presumably provided a fitness advantage for the lineage to outcompete BD-1 as the etiological agent of endemic cholera in Bangladesh, with implications for global cholera epidemiology. IMPORTANCE Cholera is a global disease with specific reference to the Bay of Bengal Ganges Delta where Vibrio cholerae O1 El Tor, the causative agent of the disease showed two circulating lineages, one dominant in Bangladesh and the other in India. Results of an in-depth genomic study of V. cholerae associated with endemic cholera during the past 27 years (1991 to 2017) indicate emergence and succession of the two lineages, BD-1 and BD-2, arising from a common ancestral paraphyletic group, BD-0, comprising the early strains and short-term evolution of the bacterium in Bangladesh. Among the two V. cholerae lineages, BD-2 supersedes BD-1 and is predominant in the most recent endemic cholera in Bangladesh. The BD-2 lineage contained significantly more SNPs and indels, and showed richness in gene abundance, including antimicrobial resistance genes, gene cassettes, and PLE to fight against bacteriophage infection, acquired over time. These findings have important epidemic implications on a global scale.

Recent chemical syntheses of bacteria related oligosaccharides using modern expeditious approaches

Apart from some essential and crucial roles in life processes carbohydrates also are involved in a few detrimental courses of action related to human health, like infections by pathogenic microbes, cancer metastasis, transplanted tissue rejection, etc. Regarding management of pathogenesis by microbes, keeping in mind of multi drug-resistant bacteria and epidemic or endemic incidents, preventive measure by vaccination is the best pathway as also recommended by the WHO; by vaccination, eradication of bacterial diseases is also possible. Although some valid vaccines based on attenuated bacterial cells or isolated pure polysaccharide-antigens or the corresponding conjugates thereof are available in the market for prevention of several bacterial diseases, but these are not devoid of some disadvantages also. In order to develop improved conjugate T-cell dependent vaccines oligosaccharides related to bacterial antigens are synthesized and converted to the corresponding carrier protein conjugates. Marketed Cuban Quimi-Hib is such a vaccine being used since 2004 to resist Haemophilus influenza b infections. During nearly the past two decades research is going on worldwide for improved synthesis of bacteria related oligosaccharides or polysaccharides towards development of such semisynthetic or synthetic glycoconjugate vaccines. The present dissertation is an endeavour to encompass the recent syntheses of several pathogenic bacterial oligosaccharides or polysaccharides, made during the past ten-eleven years with special reference to modern expeditious syntheses.

Pandemics Throughout History

The emergence and spread of infectious diseases with pandemic potential occurred regularly throughout history. Major pandemics and epidemics such as plague, cholera, flu, severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) have already afflicted humanity. The world is now facing the new coronavirus disease 2019 (COVID-19) pandemic. Many infectious diseases leading to pandemics are caused by zoonotic pathogens that were transmitted to humans due to increased contacts with animals through breeding, hunting and global trade activities. The understanding of the mechanisms of transmission of pathogens to humans allowed the establishment of methods to prevent and control infections. During centuries, implementation of public health measures such as isolation, quarantine and border control helped to contain the spread of infectious diseases and maintain the structure of the society. In the absence of pharmaceutical interventions, these containment methods have still been used nowadays to control COVID-19 pandemic. Global surveillance programs of water-borne pathogens, vector-borne diseases and zoonotic spillovers at the animal-human interface are of prime importance to rapidly detect the emergence of infectious threats. Novel technologies for rapid diagnostic testing, contact tracing, drug repurposing, biomarkers of disease severity as well as new platforms for the development and production of vaccines are needed for an effective response in case of pandemics.

Vibrio cholerae at the Intersection of Immunity and the Microbiome

Vibrio cholerae is a noninvasive pathogen that colonizes the small intestine and produces cholera toxin, causing severe secretory diarrhea. Cholera results in long lasting immunity, and recent studies have improved our understanding of the antigenic repertoire of V. cholerae Interactions between the host, V. cholerae, and the intestinal microbiome are now recognized as factors which impact susceptibility to cholera and the ability to mount a successful immune response to vaccination. Here, we review recent data and corresponding models to describe immune responses to V. cholerae infection and explain how the host microbiome may impact the pathogenesis of V. cholerae In the ongoing battle against cholera, the intestinal microbiome represents a frontier for new approaches to intervention and prevention.

Changing epidemiology and antimicrobial resistance in Vibrio cholerae: AMR surveillance findings (2006-2016) from Nepal

BACKGROUND

In Nepal, cases of Cholera occur annually either as sporadic or as outbreaks claiming the lives of many in rural areas. The present study is a laboratory based surveillance which aims to analyze the changing epidemiology and antimicrobial susceptibility trend of V. cholerae strains isolated or referred to National Public Health Laboratory (NPHL) over a period of 11 years (2006-2016).

METHODS

Specimens of fresh stool /rectal swab either received at sentinel sites or NPHL were processed following standard microbiological techniques. Suspected colonies on selective medium were identified using routine biochemical tests and confirmed by serotyping. Antimicrobial susceptibility testing was performed following Kirby Baeur disc diffusion method.

RESULTS

Of the 836 confirmed isolates, 87% (728/836) were V.cholerae O1 Ogawa,12% (103/836) were V.cholerae O1 Inaba and only 6 isolates were V.cholerae O1 Hikojima. In 2006 all the Vibrio isolates were of Inaba serotype, followed by all 3 serotypes during 2007.During 2008-2014 only Ogawa serotype was isolated while few cases of Inaba again surfaced in 2015. Resistance to ampicillin decreased from 93% in 2006 to 18% by 2010 and again raised to 100% by 2016.Cotrimoxazole resistance remained at constant range (77-100%).Nalidixic acid resistance was 100% since 2006.Ciprofloxacin and tetracycline resistance emerged in 2007, reached a peak during 2010-2012 and declined to 0 by 2016.Susceptibility to Furazolidone has re-emerged.63.6% of the isolates were Multi drug resistant.

CONCLUSION

With changing epidemiology and antibiogram of V.cholerae in Nepal, the present study reflects the importance of continuous monitoring, which could be used by policy makers and health professionals for better management of outbreaks. Decline in tetracycline and ciprofloxacin resistance along with emerging sensitivity to furazolidone shows that these drugs could make an effective comeback in future.

Cholera in selected countries in Asia

INTRODUCTION

Although the current pandemic of cholera originated in Asia, reports of cholera cases and outbreaks in the region are sparse. To provide a sub-regional assessment of cholera in South and Southeast Asia, we collated published and unpublished data from existing surveillance systems from Bangladesh, Cambodia, India, Malaysia, Nepal, Pakistan, Philippines, Thailand and Vietnam.

METHODS

Data from existing country surveillance systems on diarrhea, acute watery diarrhea, suspected cholera and/or confirmed cholera in nine selected Asian countries (Bangladesh, Cambodia, India, Malaysia, Nepal, Pakistan, Philippines, Thailand and Vietnam) from 2011 to 2015 (or 2016, when available) were collated. We reviewed annual cholera reports from WHO and searched PubMed and/or ProMED to complement data, where information is not completely available.

RESULTS

From 2011 to 2016, confirmed cholera cases were identified in at least one year of the 5- or 6-year period in the countries included. Surveillance for cholera exists in most countries, but cases are not always reported. India reported the most number of confirmed cases with a mean of 5964 cases annually. The mean number of cases per year in the Philippines, Pakistan, Bangladesh, Malaysia, Nepal and Thailand were 760, 592, 285, 264, 148 and 88, respectively. Cambodia and Vietnam reported 51 and 3 confirmed cholera cases in 2011, with no subsequent reported cases.

DISCUSSION AND CONCLUSION

We present consolidated results of available surveillance in nine Asian countries and supplemented these with publication searches. There is paucity of readily accessible data on cholera in these countries. We highlight the continuing existence of the disease even in areas with improved sanitation and access to safe drinking water. Continued vigilance and improved surveillance in countries should be strongly encouraged.

Genomic comparison of serogroups O159 and O170 with other Vibrio cholerae serogroups

Background

Of the hundreds of Vibrio cholerae serogroups, O1 and O139 are the main epidemic-causing ones. Although non-O1/non-O139 serogroups rarely cause epidemics, the possibility exists for strains within them to have pathogenic potential.

Results

We selected 25 representative strains within 16 V. cholerae serogroups and examined their genomic and functional characteristics. We tentatively constructed a gene pool containing 405 homologous gene clusters, which is well organized and functions in O-antigen polysaccharide (O-PS) synthesis. Our network analysis indicate that great diversity exists in O-PS among the serogroups, and several serogroup pairs share a high number of homologous genes (e.g., O115 and O37; O170 and O139; O12 and O39). The phylogenetic analysis results suggest that a close relationship exists between serogroups O170, O89 and O144, based on neighbor-joining (NJ) and gene trees, although serogroup O159 showed an inconsistent phylogenetic relationship between the NJ tree and the gene tree, indicating that it may have undergone extensive recombination and horizontal gene transfer. Different phylogenetic structures were observed between the core genes, pan genes, and O-PS genes. The virulence gene analysis indicated that the virulence genes from all the representative strains may have their sources from four particular bacteria (Pseudomonas aeruginosa, V. vulnificus, Haemophilus somnus and H. influenzae), which suggests that V. cholerae may have exchanged virulence genes with other bacterial genera or species in certain environments. The mobile genetic element analysis indicated that O159 carries nearly complete VSP-II and partial VPI-1 and VPI-2, O170 carries partial VPI-1 and VPI-2, and several non-O1/non-O139 strains contain full or partial VPI-1 and VPI-2. Several genes showing evidence of positive selection are involved in chemotaxis, Na + resistance, or cell wall synthesis, suggestive of environmental adaptation.

Conclusions

This study reports on the newly sequenced O159 and O170 genomes and their comparisons with other V. cholerae serogroups. The complicated O-PS network of constituent genes highlights the detailed recombination mechanisms that have acted on the serogroups’ genomes. The serogroups have different virulence-related gene profiles, and there is evidence of positive selection acting on other genes, possibly during adaptation to different environments and hosts.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5603-7) contains supplementary material, which is available to authorized users.

Water-soluble cranberry extract inhibits Vibrio cholerae biofilm formation possibly through modulating the second messenger 3', 5' - Cyclic diguanylate level

Quorum sensing (QS) and nucleotide-based second messengers are vital signaling systems that regulate bacterial physiology in response to changing environments. Disrupting bacterial signal transduction is a promising direction to combat infectious diseases, and QS and the second messengers are undoubtedly potential targets. In Vibrio cholerae, both QS and the second messenger 3’, 5’—cyclic diguanylate (c-di-GMP) play a central role in controlling motility, motile-to-sessile life transition, and virulence. In this study, we found that water-soluble extract from the North American cranberry could significantly inhibit V. cholerae biofilm formation during the development/maturation stage by reducing the biofilm matrix production and secretion. The anti-biofilm effect by water-soluble cranberry extract was possibly through modulating the intracellular c-di-GMP level and was independent of QS and the QS master regulator HapR. Our results suggest an opportunity to explore more functional foods to fight stubborn infections through interference with the bacterial signaling systems.

Genotypic and Phenotypic Assays to Distinguish Vibrio cholerae Biotype

Vibrio cholerae is a motile gram-negative bacterium found in brackish water and the etiological agent of the fecal-oral disease cholera. Classical and El Tor are two main biotypes that make up the V. cholerae O1 serogroup, which each display unique genotypic and phenotypic characteristics that allow for reliable biotype characterization. While treatment for cholera is much the same despite the causative strain's biotype, such classification can be imperative for laboratory experiments and may have broader impacts in the biomedical field. In the early 2000s, clinical isolates were identified that contained genotypic and phenotypic traits from both biotypes. The newly identified hybrids, termed El Tor variants, have caused clinical and environmental isolate biotype identification to be more complicated than previous single-assay identification. Herein, we describe a series of PCR-based genetic screens (tcpA and ctxB) and phenotypic assays (polymyxin B resistance, citrate metabolism, proteolytic activity, hemolytic activity, motility, and Voges-Proskauer). Together, these assays are used for reliable biotype characterization of V. cholerae clinical (and environmental) isolates.

Prevalence of Vibrio cholerae in Coastal Alternative Supplies of Drinking Water and Association with Bacillus-Like Spore Formers

The scarcity of hygienic drinking water is a normal phenomenon in the coastal areas of Bangladesh due to the high salinity of ground water. The inhabitants of this locality, therefore, live on alternative supplies of water including rain-fed pond water, and rainwater with persistent complex microbial interactions therein, often contaminated with life-threatening pathogens. Hence, this study was aimed at analyzing the prevalence of Vibrio cholerae (Vc) in the alternative drinking waters of Mathbaria, a coastal subdistrict neighboring the Bay of Bengal, the efficacy of pond sand filter (PSF) and the co-association among Bacillus-like spore formers (Sf) and Vc. Vc presumably entrapped into the membrane filter was enriched in alkaline peptone water medium and was isolated on selective thiosulfate-citrate-bile salts-sucrose and taurocholate-tellurite-gelatin agar media. They were finally identified by immunochromatographic one step rapid test and serology test. A total of 26% Vc positive samples were obtained out of 100 [ponds—48, household (HH)—29, and PSFs—23] where 13% cases were pathogenic (Vc O1) and 13% were non-pathogenic (Vc non-O1/non-O139). The distribution of Vc as observed was 33, 26, and 13.8% in waters derived from pond surface, PSF, and HH reservoirs, respectively, and for pathogenic type, it was 62.5%, 50%, and nil, respectively. Although none of the samples was identified with pathogenic Vc O139, the statistics represents a significant and augmentative risk of cholera outbreak in the focused area. The antibiotic sensitivity pattern in this study resembled the trend observed during last few years for Vc. The PSF demonstrated its inability to remove Vc from any of the samples and in addition, the filter itself was evidenced to be the source of pathogens and spores in further contamination and transmission. The development of biofilm in the PSF could be hypothesized as the reservoir in contaminating pathogen-free water samples. From the test of homogeneity, the risk levels of alternative water sources were estimated equal regarding Vc. Simultaneously, it was determined statistically that the prevalence of Vc, by no means, is influenced by Bacillus-like Sf be it for pond surface, HH, or PSF derived water.

Vibrio cholerae Colonization of Soft-Shelled Turtles

Vibrio cholerae is an important human pathogen and environmental microflora species that can both propagate in the human intestine and proliferate in zooplankton and aquatic organisms. Cholera is transmitted through food and water. In recent years, outbreaks caused by V. cholerae-contaminated soft-shelled turtles, contaminated mainly with toxigenic serogroup O139, have been frequently reported, posing a new foodborne disease public health problem. In this study, the colonization by toxigenic V. cholerae on the body surfaces and intestines of soft-shelled turtles was explored. Preferred colonization sites on the turtle body surfaces, mainly the carapace and calipash of the dorsal side, were observed for the O139 and O1 strains. Intestinal colonization was also found. The colonization factors of V. cholerae played different roles in the colonization of the soft-shelled turtle's body surface and intestine. Mannose-sensitive hemagglutinin (MSHA) of V. cholerae was necessary for body surface colonization, but no roles were found for toxin-coregulated pili (TCP) or N-acetylglucosamine-binding protein A (GBPA). Both TCP and GBPA play important roles for colonization in the intestine, whereas the deletion of MSHA revealed only a minor colonization-promoting role for this factor. Our study demonstrated that V. cholerae can colonize the surfaces and the intestines of soft-shelled turtles and indicated that the soft-shelled turtles played a role in the transmission of cholera. In addition, this study showed that the soft-shelled turtle has potential value as an animal model in studies of the colonization and environmental adaption mechanisms of V. cholerae in aquatic organisms.IMPORTANCE Cholera is transmitted through water and food. Soft-shelled turtles contaminated with Vibrio cholerae (commonly the serogroup O139 strains) have caused many foodborne infections and outbreaks in recent years, and they have become a foodborne disease problem. Except for epidemiological investigations, no experimental studies have demonstrated the colonization by V. cholerae on soft-shelled turtles. The present studies will benefit our understanding of the interaction between V. cholerae and the soft-shelled turtle. We demonstrated the colonization by V. cholerae on the soft-shelled turtle's body surface and in the intestine and revealed the different roles of major V. cholerae factors for colonization on the body surface and in the intestine. Our work provides experimental evidence for the role of soft-shelled turtles in cholera transmission. In addition, this study also shows the possibility for the soft-shelled turtle to serve as a new animal model for studying the interaction between V. cholerae and aquatic hosts.

Pandemics, pathogenicity and changing molecular epidemiology of cholera in the era of global warming

Background

Vibrio cholerae, a Gram-negative, non-spore forming curved rod is found in diverse aquatic ecosystems around the planet. It is classified according to its major surface antigen into around 206 serogroups, of which O1 and O139 cause epidemic cholera. A recent spatial modelling technique estimated that around 2.86 million cholera cases occur globally every year, and of them approximately 95,000 die. About 1.3 billion people are currently at risk of infection from cholera. Meta-analysis and mathematical modelling have demonstrated that due to global warming the burden of vector-borne diseases like malaria, leishmaniasis, meningococcal meningitis, viral encephalitis, dengue and chikungunya will increase in the coming years in the tropics and beyond.

Cholera and climate

This review offers an overview of the interplay between global warming and the pathogenicity and epidemiology of V. cholerae. Several distinctive features of cholera survival (optimal thriving at 15% salinity, 30 °C water temperature, and pH 8.5) indicate a possible role of climate change in triggering the epidemic process. Genetic exchange (ctxAB, zot, ace, cep, and orfU) between strains and transduction process allows potential emergence of new toxigenic clones. These processes are probably controlled by precise environmental signals such as optimum temperature, sunlight and osmotic conditions. Environmental influences on phytoplankton growth and chitin remineralization will be discussed alongside the interplay of poor sanitary conditions, overcrowding, improper sewage disposal and global warming in promoting the growth and transmission of this deadly disease.

Conclusion

The development of an effective early warning system based on climate data could help to prevent and control future outbreaks. It may become possible to integrate real-time monitoring of oceanic regions, climate variability and epidemiological and demographic population dynamics to predict cholera outbreaks and support the design of cost-effective public health strategies.

Vibrio cholerae O1 with Reduced Susceptibility to Ciprofloxacin and Azithromycin Isolated from a Rural Coastal Area of Bangladesh

Cholera outbreaks occur each year in the remote coastal areas of Bangladesh and epidemiological surveillance and routine monitoring of cholera in these areas is challenging. In this study, a total of 97 Vibrio cholerae O1 isolates from Mathbaria, Bangladesh, collected during 2010 and 2014 were analyzed for phenotypic and genotypic traits, including antimicrobial susceptibility. Of the 97 isolates, 95 possessed CTX-phage mediated genes, ctxA, ace, and zot, and two lacked the cholera toxin gene, ctxA. Also both CTX⁺ and CTX⁻V. cholerae O1 isolated in this study carried rtxC, tcpA^ET, and hlyA. The classical cholera toxin gene, ctxB1, was detected in 87 isolates, while eight had ctxB7. Of 95 CTX⁺V. cholerae O1, 90 contained rstR^ET and 5 had rstR^CL. All isolates, except two, contained SXT related integrase intSXT. Resistance to penicillin, streptomycin, nalidixic acid, sulfamethoxazole-trimethoprim, erythromycin, and tetracycline varied between the years of study period. Most importantly, 93% of the V. cholerae O1 were multidrug resistant. Six different resistance profiles were observed, with resistance to streptomycin, nalidixic acid, tetracycline, and sulfamethoxazole-trimethoprim predominant every year. Ciprofloxacin and azithromycin MIC were 0.003–0.75 and 0.19–2.00 μg/ml, respectively, indicating reduced susceptibility to these antibiotics. Sixteen of the V. cholerae O1 isolates showed higher MIC for azithromycin (≥0.5 μg/ml) and were further examined for 10 macrolide resistance genes, erm(A), erm(B), erm(C), ere(A), ere(B), mph(A), mph(B), mph(D), mef(A), and msr(A) with none testing positive for the macrolide resistance genes.

Characterization and Genetic Variation of Vibrio cholerae Isolated from Clinical and Environmental Sources in Thailand

Cholera is still an important public health problem in several countries, including Thailand. In this study, a collection of clinical and environmental V. cholerae serogroup O1, O139, and non-O1/non-O139 strains originating from Thailand (1983 to 2013) was characterized to determine phenotypic and genotypic traits and to investigate the genetic relatedness. Using a combination of conventional methods and whole genome sequencing (WGS), 78 V. cholerae strains were identified. WGS was used to determine the serogroup, biotype, virulence, mobile genetic elements, and antimicrobial resistance genes using online bioinformatics tools. In addition, phenotypic antimicrobial resistance was determined by the minimal inhibitory concentration (MIC) test. The 78 V. cholerae strains belonged to the following serogroups O1: (n = 44), O139 (n = 16) and non-O1/non-O139 (n = 18). Interestingly, we found that the typical El Tor O1 strains were the major cause of clinical cholera during 1983–2000 with two Classical O1 strains detected in 2000. In 2004–2010, the El Tor variant strains revealed genotypes of the Classical biotype possessing either only ctxB or both ctxB and rstR while they harbored tcpA of the El Tor biotype. Thirty O1 and eleven O139 clinical strains carried CTXϕ (Cholera toxin) and tcpA as well four different pathogenic islands (PAIs). Beside non-O1/non-O139, the O1 environmental strains also presented chxA and Type Three Secretion System (TTSS). The in silico MultiLocus Sequence Typing (MLST) discriminated the O1 and O139 clinical strains from other serogroups and environmental strains. ST69 was dominant in the clinical strains belonging to the 7^th pandemic clone. Non-O1/non-O139 and environmental strains showed various novel STs indicating genetic variation. Multidrug-resistant (MDR) strains were observed and conferred resistance to ampicillin, azithromycin, nalidixic acid, sulfamethoxazole, tetracycline, and trimethoprim and harboured variants of the SXT elements.

For the first time since 1986, the presence of V. cholerae O1 Classical was reported causing cholera outbreaks in Thailand. In addition, we found that V. cholerae O1 El Tor variant and O139 were pre-dominating the pathogenic strains in Thailand. Using WGS and bioinformatic tools to analyze both historical and contemporary V. cholerae circulating in Thailand provided a more detailed understanding of the V. cholerae epidemiology, which ultimately could be applied for control measures and management of cholera in Thailand.

Total Synthesis of the Complete Protective Antigen of Vibrio cholerae O139

The first chemical synthesis of the complete protective O-antigen of a human-disease-causing pathogenic bacterium is described. The synthesis involved a protecting-group strategy that facilitated the regioselectivity of the key transformations, stereoselective glycosylation reactions, and enabled the one-step global deprotection of the completely assembled, fully protected, phosphorylated hexasaccharide by hydrogenation/hydrogenolysis. The final amino-group-functionalized, linker-equipped antigen was obtained in a form ready for conjugation to suitable carriers, for example, proteins, to yield immunogens.

Single Nucleotide Polymorphisms in Regulator-Encoding Genes Have an Additive Effect on Virulence Gene Expression in a Vibrio cholerae Clinical Isolate

Cholera, an infectious disease of the small intestine caused by the aquatic bacterium Vibrio cholerae, often results in vomiting and acute watery diarrhea. If left untreated or if the response is too slow, the symptoms can quickly lead to extreme dehydration and ultimately death of the patient. Recent anecdotal evidence of cholera patients suffering from increasingly severe symptoms and of disease progression at a much higher rate than previously observed has emerged. As recent cholera outbreaks caused by increasingly virulent strains have resulted in higher mortality rates, the need to investigate the mechanism(s) allowing this observed increased virulence is apparent. The significance of our research is in identifying the mechanism for increased virulence capabilities, which will allow the development of a model that will greatly enhance our understanding of cholera disease and V. cholerae pathogenesis, leading to broader biomedical impacts, as cholera serves as a model for other enteric diarrheal diseases.

Vibrio cholerae is the etiological agent of the infectious disease cholera, which is characterized by vomiting and severe watery diarrhea. Recently, V. cholerae clinical isolates have demonstrated increased virulence capabilities, causing more severe symptoms with a much higher rate of disease progression than previously observed. We have identified single nucleotide polymorphisms (SNPs) in four virulence-regulatory genes (hapR, hns, luxO, and vieA) of a hypervirulent V. cholerae clinical isolate, MQ1795. Herein, all SNPs and SNP combinations of interest were introduced into the prototypical El Tor reference strain N16961, and the effects on the production of numerous virulence-related factors, including cholera toxin (CT), the toxin-coregulated pilus (TCP), and ToxT, were analyzed. Our data show that triple-SNP (hapR hns luxO and hns luxO vieA) and quadruple-SNP combinations produced the greatest increases in CT, TCP, and ToxT production. The hns and hns luxO SNP combinations were sufficient for increased TCP and ToxT production. Notably, the hns luxO vieA triple-SNP combination strain produced TCP and ToxT levels similar to those of MQ1795. Certain SNP combinations (hapR and hapR vieA) had the opposite effect on CT, TCP, and ToxT expression. Interestingly, the hns vieA double-SNP combination strain increased TCP production while decreasing CT production. Our findings suggest that SNPs identified in the four regulatory genes, in various combinations, are associated with increased virulence capabilities observed in V. cholerae clinical isolates. These studies provide insight into the evolution of highly virulent strains.

IMPORTANCE Cholera, an infectious disease of the small intestine caused by the aquatic bacterium Vibrio cholerae, often results in vomiting and acute watery diarrhea. If left untreated or if the response is too slow, the symptoms can quickly lead to extreme dehydration and ultimately death of the patient. Recent anecdotal evidence of cholera patients suffering from increasingly severe symptoms and of disease progression at a much higher rate than previously observed has emerged. As recent cholera outbreaks caused by increasingly virulent strains have resulted in higher mortality rates, the need to investigate the mechanism(s) allowing this observed increased virulence is apparent. The significance of our research is in identifying the mechanism for increased virulence capabilities, which will allow the development of a model that will greatly enhance our understanding of cholera disease and V. cholerae pathogenesis, leading to broader biomedical impacts, as cholera serves as a model for other enteric diarrheal diseases.

Molecular epidemiology of Vibrio cholerae O1 in northern Vietnam (2007-2009), using multilocus variable-number tandem repeat analysis

Cholera is an infectious disease of major concern in Vietnam and other Asian countries. In 2009, there was a large outbreak of cholera in northern Vietnam. To investigate relationships among isolates of the causative pathogen Vibrio cholerae in this region since 2007, we carried out a multilocus variable-number tandem repeat analysis (MLVA) of 170 isolates collected between 2007 and 2009. A total of 24 MLVA types were identified using seven loci. Five clones (1-5) were identified using five loci of the large V. cholerae chromosome; clones 1 and 2 were major, and the others were minor. Clone 1 isolates were responsible for the 2009 outbreak. A shift in the predominant clone occurred between 2007 and 2009, with clone 1 likely derived from clone 2. Moreover, the former was less diverse than the latter, suggesting a single source of cholera dissemination. Epidemiological data indicated a wavelet prior to the large outbreak, suggesting that drinking water source or food chain became contaminated during dissemination. Our results reveal the utility of MLVA for analysis of V. cholerae isolates within a relatively short period and broaden our understanding of its transmission and response to cholera.

Genetic relatedness of selected clinical Vibrio cholerae O139 isolates from the southern coastal area of China over a 20-year period

Vibrio cholerae O139 emerged as a causative agent of epidemic cholera in 1992 in India and Bangladesh, and was subsequently reported in China in 1993. The genetic relatedness and molecular characteristics of V. cholerae O139 in Guangdong Province, located in the southern coastal area of China, remains undetermined. In this study, we investigated 136 clinical V. cholerae O139 isolates from 1993 to 2013 in Guangdong. By conventional PCR, 123 (90·4%) isolates were positive for ctxB, ace and zot. Sequencing of the positive amplicons indicated 113 (91·7%) isolates possessed the El Tor allele of ctxB (genotype 3); seven carried the classical ctxB type (genotype 1) and three harboured a novel ctxB type (genotype 5). With respect to tcpA, 123 (90·4%) isolates were positive for the El Tor allele. In addition, pulsed-field gel electrophoresis (with NotI digestion) differentiated the isolates into clusters A and B. Cluster A contained seven of the non-toxigenic isolates from 1998 to 2000; another six non-toxigenic isolates (from 1998 and 2007) and all of the toxigenic isolates formed cluster B. Our results suggest that over a 20-year period, the predominant O139 clinical isolates have maintained a relatively tight clonal structure, although some genetic variance and shift has occurred. Our data highlight the persistence of toxigenic V. cholerae O139 in clinical settings in the southern coastal area of China.

Phylogenetic Diversity of Vibrio cholerae Associated with Endemic Cholera in Mexico from 1991 to 2008

An outbreak of cholera occurred in 1991 in Mexico, where it had not been reported for more than a century and is now endemic. Vibrio cholerae O1 prototype El Tor and classical strains coexist with altered El Tor strains (1991 to 1997). Nontoxigenic (CTX⁻) V. cholerae El Tor dominated toxigenic (CTX⁺) strains (2001 to 2003), but V. cholerae CTX⁺ variant El Tor was isolated during 2004 to 2008, outcompeting CTX⁻V. cholerae. Genomes of six Mexican V. cholerae O1 strains isolated during 1991 to 2008 were sequenced and compared with both contemporary and archived strains of V. cholerae. Three were CTX⁺ El Tor, two were CTX⁻ El Tor, and the remaining strain was a CTX⁺ classical isolate. Whole-genome sequence analysis showed the six isolates belonged to five distinct phylogenetic clades. One CTX⁻ isolate is ancestral to the 6th and 7th pandemic CTX⁺V. cholerae isolates. The other CTX⁻ isolate joined with CTX⁻ non-O1/O139 isolates from Haiti and seroconverted O1 isolates from Brazil and Amazonia. One CTX⁺ isolate was phylogenetically placed with the sixth pandemic classical clade and the V. cholerae O395 classical reference strain. Two CTX⁺ El Tor isolates possessing intact Vibrio seventh pandemic island II (VSP-II) are related to hybrid El Tor isolates from Mozambique and Bangladesh. The third CTX⁺ El Tor isolate contained West African-South American (WASA) recombination in VSP-II and showed relatedness to isolates from Peru and Brazil. Except for one isolate, all Mexican isolates lack SXT/R391 integrative conjugative elements (ICEs) and sensitivity to selected antibiotics, with one isolate resistant to streptomycin. No isolates were related to contemporary isolates from Asia, Africa, or Haiti, indicating phylogenetic diversity.

Sequencing of genomes of V. cholerae is critical if genetic changes occurring over time in the circulating population of an area of endemicity are to be understood. Although cholera outbreaks occurred rarely in Mexico prior to the 1990s, genetically diverse V. cholerae O1 strains were isolated between 1991 and 2008. Despite the lack of strong evidence, the notion that cholera was transmitted from Africa to Latin America has been proposed in the literature. In this study, we have applied whole-genome sequence analysis to a set of 124 V. cholerae strains, including six Mexican isolates, to determine their phylogenetic relationships. Phylogenetic analysis indicated the six V. cholerae O1 isolates belong to five phylogenetic clades: i.e., basal, nontoxigenic, classical, El Tor, and hybrid El Tor. Thus, the results of phylogenetic analysis, coupled with CTXϕ array and antibiotic susceptibility, do not support single-source transmission of cholera to Mexico from African countries. The association of indigenous populations of V. cholerae that has been observed in this study suggests it plays a significant role in the dynamics of cholera in Mexico.

Regulation of competence-mediated horizontal gene transfer in the natural habitat of Vibrio cholerae

The human pathogen Vibrio cholerae is an autochthonous inhabitant of aquatic environments where it often interacts with zooplankton and their chitinous molts. Chitin induces natural competence for transformation in V. cholerae, a key mode of horizontal gene transfer (HGT). Recent comparative genomic analyses were indicative of extensive HGT in this species. However, we can still expand our understanding of the complex regulatory network that drives competence in V. cholerae. Here, we present recent advances, including the elucidation of bipartite competence regulation mediated by QstR, the inclusion of the type VI secretion system in the competence regulon of pandemic O1 El Tor strains, and the identification of TfoS as a transcriptional regulator that links chitin to competence induction in V. cholerae.

Distribution and molecular characteristics of Vibrio cholerae O1 El Tor isolates recovered in Guangdong Province, China, 1961-2013

China's Guangdong Province is located along the same latitude as Kolkata, India and Dhaka, Bangladesh, and is also considered a source of epidemic cholera. However, molecular description and the genetic relationships between Vibrio cholerae O1 El Tor isolates in Guangdong remain unclear. In this study, 381 clinical V. cholerae O1 isolates recovered from cholera cases presenting in Guangdong between 1961 and 2013 were investigated by PCR, amplicon sequencing and pulsed-field gel electrophoresis (PFGE). During this time frame, four distinct epidemic periods (1-4) were observed based on the different dominant serotype leading its epidemic, correspond to years; or time periods from/to 1961-1969, 1978-1989, 1990-2000, 2001-2013, respectively. Molecular analysis of representative isolates indicated that a single dominating clone was associated with each epidemic stage. All isolates from periods 1 and 2 carried the typical El Tor ctxB; this allele was displaced by classical ctxB beginning in 1993. However all isolates carried the El Tor-specific toxin-coregulated pili subunit A (tcpA). Isolates were grouped into five clusters on the basis of Not I enzyme digested PFGE, and the first four clusters were associated with specific periods, cluster I (period 1), II (period 3), III (period 2) and IV (period 4), respectively. While cluster V consisted of isolates from all four epidemic periods, but was most heterogeneous in appearance. Our data indicate genetic variations that shape the relationship among emerging isolates of V. cholerae O1 in Guangdong Province contribute to the 7th global pandemic.

A single point mutation within the coding sequence of cholera toxin B subunit will increase its expression yield

Background: Cholera toxin B subunit (CTB) has been extensively considered as an immunogenic and adjuvant protein, but its yield of expression is not satisfactory in many studies. The aim of this study was to compare the expression of native and mutant recombinant CTB (rCTB) in pQE vector. Methods: ctxB fragment from Vibrio cholerae O₁ ATCC14035 containing the substitution of mutant ctxB for amino acid S128T was amplified by PCR and cloned in pGETM-T easy vector. It was then transformed to E. coli Top 10F' and cultured on LB agar plate containing ampicillin. Sequence analysis confirmed the mature ctxB gene sequence and the mutant one in both constructs which were further subcloned to pQE-30 vector. Both constructs were subsequently transformed to E. coli M15 (pREP4) for expression of mature and mutant rCTB. Results: SDS-PAGE analysis showed the maximum expression of rCTB in both systems at 5 hours after induction and Western-blot analysis confirmed the presence of rCTB in blotting membranes. The expression of mutant rCTB was much higher than mature rCTB, which may be the result of serine-to-threonine substitution at position 128 of mature rCTB amino acid sequence created by PCR mutagenesis. The mutant rCTB retained pentameric stability and its ability to bind to anti- cholera toxin IgG antibodies. Conclusion: Point mutation in ctxB sequence resulted in over-expression of rCTB, probably due to the increase of solubility of produced rCTB. Consequently, this expression system can be used to produce rCTB in high yield.

IncA/C plasmids harboured in serious multidrug-resistant Vibrio cholerae serogroup O139 strains in China

Vibrio cholerae serogroup O139 emerged in 1992 and is one of two major serogroups to have caused cholera epidemics. After 1998, serious multidrug-resistant (MDR) O139 strains quickly became common in China, showing a multidrug resistance profile to eight antibiotics. It is a great threat to public health, and elucidation of its mechanisms of resistance will provide a helpful guide for the clinical treatment and prevention of cholera. In this study, mega-plasmids from MDR V. cholerae O139 strains were identified by pulsed-field gel electrophoresis (PFGE) without enzyme digestion. One plasmid was isolated and sequenced, belonging to the IncA/C family. Ten antibiotic resistance genes were found in the MDR regions, including a blaTEM-20 gene, and these genes endowed the host with resistance to seven antibiotics. This kind of plasmid was positive in 71.2% (198/278) of toxigenic O139 strains, and the rate of plasmid positivity was consistent with the yearly change in MDR rates of these strains. This study reveals an important role of the IncA/C family plasmid in the spread of multiple antibiotic resistance of epidemic V. cholerae serogroup O139 strains, which has recombined with plasmids from different bacterial species and transferred among V. cholerae strains.

Cholera outbreaks in the El Tor biotype era and the impact of the new El Tor variants

Vibrio cholerae O1, the causative agent of the disease cholera, has two biotypes namely the classical and El Tor. Biotype is a subspecific taxonomic classification of V. cholerae O1. Differentiation of V. cholerae strains into biotype does not alter the clinical management of cholera but is of immense public health and epidemiological importance in identifying the source and spread of infection, particularly when V. cholerae is first isolated in a country or geographic area. From recorded history, till date, the world has experienced seven pandemics of cholera. Among these, the first six pandemics are believed to have been caused by the classical biotype whereas the ongoing seventh pandemic is caused by the El Tor biotype. In recent years, new pathogenic variants of V. cholerae have emerged and spread throughout many Asian and African countries with corresponding cryptic changes in the epidemiology of cholera. In this chapter, we describe the outbreaks during the seventh pandemic El Tor biotype era spanning more than five decades along with the recent advances in our understanding of the development, evolution, spread, and impact of the new variants of El Tor strains.

Cholera outbreaks (2012) in three districts of Nepal reveal clonal transmission of multi-drug resistant Vibrio cholerae O1

Background

Although endemic cholera causes significant morbidity and mortality each year in Nepal, lack of information about the causal bacterium often hinders cholera intervention and prevention. In 2012, diarrheal outbreaks affected three districts of Nepal with confirmed cases of mortality. This study was designed to understand the drug response patterns, source, and transmission of Vibrio cholerae associated with 2012 cholera outbreaks in Nepal.

Methods

V. cholerae (n = 28) isolated from 2012 diarrhea outbreaks {n = 22; Kathmandu (n = 12), Doti (n = 9), Bajhang (n = 1)}, and surface water (n = 6; Kathmandu) were tested for antimicrobial response. Virulence properties and DNA fingerprinting of the strains were determined by multi-locus genetic screening employing polymerase chain reaction, DNA sequencing, and pulsed-field gel electrophoresis (PFGE).

Results

All V. cholerae strains isolated from patients and surface water were confirmed to be toxigenic, belonging to serogroup O1, Ogawa serotype, biotype El Tor, and possessed classical biotype cholera toxin (CTX). Double-mismatch amplification mutation assay (DMAMA)-PCR revealed the V. cholerae strains to possess the B-7 allele of ctx subunit B. DNA sequencing of tcpA revealed a point mutation at amino acid position 64 (N → S) while the ctxAB promoter revealed four copies of the tandem heptamer repeat sequence 5'-TTTTGAT-3'. V. cholerae possessed all the ORFs of the Vibrio seventh pandemic island (VSP)-I but lacked the ORFs 498–511 of VSP-II. All strains were multidrug resistant with resistance to trimethoprim-sulfamethoxazole (SXT), nalidixic acid (NA), and streptomycin (S); all carried the SXT genetic element. DNA sequencing and deduced amino acid sequence of gyrA and parC of the NA^R strains (n = 4) revealed point mutations at amino acid positions 83 (S → I), and 85 (S → L), respectively. Similar PFGE (NotI) pattern revealed the Nepalese V. cholerae to be clonal, and related closely with V. cholerae associated with cholera in Bangladesh and Haiti.

Conclusions

In 2012, diarrhea outbreaks in three districts of Nepal were due to transmission of multidrug resistant V. cholerae El Tor possessing cholera toxin (ctx) B-7 allele, which is clonal and related closely with V. cholerae associated with cholera in Bangladesh and Haiti.

Widespread epidemic cholera caused by a restricted subset of Vibrio cholerae clones

Since 1817, seven cholera pandemics have plagued humankind. As the causative agent, Vibrio cholerae, is autochthonous in the aquatic ecosystem and some studies have revealed links between outbreaks and fluctuations in climatic and aquatic conditions, it has been widely assumed that cholera epidemics are triggered by environmental factors that promote the growth of local bacterial reservoirs. However, mounting epidemiological findings and genome sequence analysis of clinical isolates have indicated that epidemics are largely unassociated with most of the V. cholerae strains in aquatic ecosystems. Instead, only a specific subset of V. cholerae El Tor 'types' appears to be responsible for current epidemics. A recent report examining the evolution of a variety of V. cholerae strains indicates that the current pandemic is monophyletic and originated from a single ancestral clone that has spread globally in successive waves. In this review, we examine the clonal nature of the disease, with the example of the recent history of cholera in the Americas. Epidemiological data and genome sequence-based analysis of V. cholerae isolates demonstrate that the cholera epidemics of the 1990s in South America were triggered by the importation of a pathogenic V. cholerae strain that gradually spread throughout the region until local outbreaks ceased in 2001. Latin America remained almost unaffected by the disease until a new toxigenic V. cholerae clone was imported into Haiti in 2010. Overall, cholera appears to be largely caused by a subset of specific V. cholerae clones rather than by the vast diversity of V. cholerae strains in the environment.

Genome sequence and comparative analysis of a Vibrio cholerae O139 strain E306 isolated from a cholera case in China

Background

Vibrio cholerae is a human intestinal pathogen and V. cholerae of the O139 serogroups are responsible for the current epidemic cholera in China. In this work, we reported the whole genome sequencing of a V. cholerae O139 strain E306 isolated from a cholera patient in the 306th Hospital of PLA, Beijing, China.

Results

We obtained the draft genome of V. cholerae O139 strain E306 with a length of 4,161,908 bps and mean G + C content of 47.7%. Phylogenetic analysis indicated that strain E306 was very close to another O139 strain, V. cholerae MO10, which was isolated during the cholera outbreak in India and Bangladesh. However, unlike MO10, strain E306 harbors the El Tor-specific RS1 element with no pre-CTX prophage (VSK), very similar to those found in some V. cholerae O1 strains. In addition, strain E306 contains a SXT/R391 family integrative conjugative element (ICE) similar to ICEVchInd4 and SXT ^MO10, and it carries more antibiotic resistance genes than other closest neighbors.

Conclusions

The genome sequence of the V. cholerae O139 strain E306 and its comparative analysis with other V. cholerae strains we present here will provide important information for a better understanding of the pathogenicity of V. cholerae and their molecular mechanisms to adapt different environments.

Construction and evaluation of V. cholerae O139 mutant, VCUSM21P, as a safe live attenuated cholera vaccine

Cholera is a major infectious disease, affecting millions of lives annually. In endemic areas, implementation of vaccination strategy against cholera is vital. As the use of safer live vaccine that can induce protective immunity against Vibrio cholerae O139 infection is a promising approach for immunization, we have designed VCUSM21P, an oral cholera vaccine candidate, which has ctxA that encodes A subunit of ctx and mutated rtxA/C, ace and zot mutations. VCUSM21P was found not to disassemble the actin of HEp2 cells. It colonized the mice intestine approximately 1 log lower than that of the Wild Type (WT) strain obtained from Hospital Universiti Sains Malaysia. In the ileal loop assay, unlike WT challenge, 1×10⁶ and 1×10⁸ colony forming unit (CFU) of VCUSM21P was not reactogenic in non-immunized rabbits. Whereas, the reactogenicity caused by the WT in rabbits immunized with 1×10¹⁰ CFU of VCUSM21P was found to be reduced as evidenced by absence of fluid in loops administered with 1×10²–1×10⁷ CFU of WT. Oral immunization using 1×10¹⁰ CFU of VCUSM21P induced both IgA and IgG against Cholera Toxin (CT) and O139 lipopolysaccharides (LPS). The serum vibriocidal antibody titer had a peak rise of 2560 fold on week 4. Following Removable Intestinal Tie Adult Rabbit Diarrhoea (RITARD) experiment, the non-immunized rabbits were found not to be protected against lethal challenge with 1×10⁹ CFU WT, but 100% of immunized rabbits survived the challenge. In the past eleven years, V. cholerae O139 induced cholera has not been observed. However, attenuated VCUSM21P vaccine could be used for vaccination program against potentially fatal endemic or emerging cholera caused by V. cholerae O139.

A molecular surveillance reveals the prevalence of Vibrio cholerae O139 isolates in China from 1993 to 2012

Vibrio cholerae serogroup O139 was first identified in 1992 in India and Bangladesh, in association with major epidemics of cholera in both countries; cases were noted shortly thereafter in China. We characterized 211 V. cholerae O139 isolates that were isolated at multiple sites in China between 1993 and 2012 from patients (n = 92) and the environment (n = 119). Among clinical isolates, 88 (95.7%) of 92 were toxigenic, compared with 47 (39.5%) of 119 environmental isolates. Toxigenic isolates carried the El Tor CTX prophage and toxin-coregulated pilus A gene (tcpA), as well as the Vibrio seventh pandemic island I (VSP-I) and VSP-II. Among a subset of 42 toxigenic isolates screened by multilocus sequence typing (MLST), all were in the same sequence type as a clinical isolate (MO45) from the original Indian outbreak. Nontoxigenic isolates, in contrast, generally lacked VSP-I and -II, and fell within 13 additional sequence types in two clonal complexes distinct from the toxigenic isolates. In further pulsed-field gel electrophoresis (PFGE) (with NotI digestion) studies, toxigenic isolates formed 60 pulsotypes clustered in one group, while the nontoxigenic isolates formed 43 pulsotypes which clustered into 3 different groups. Our data suggest that toxigenic O139 isolates from widely divergent geographic locations, while showing some diversity, have maintained a relatively tight clonal structure across a 20-year time span. Nontoxigenic isolates, in contrast, exhibited greater diversity, with multiple clonal lineages, than did their toxigenic counterparts.

Postgenomic approaches to cholera vaccine development

Cholera remains an important public health threat. A cholera vaccine that provides durable protection at the mucosal surface, especially among children in endemic settings, is urgently needed. The availability of the complete genome sequence of a clinical isolate of Vibrio cholerae O1 El Tor has allowed for comparative and functional genomic approaches in the study of cholera. This work holds promise for the identification of bacterial targets of protective human immune responses and may contribute to the development of a new generation of cholera vaccines.

Cholera outbreaks in South-East Asia

This chapter highlights the cholera situation in South Asia and the Bay of Bengal region, the original 'homeland' of cholera. A detailed discussion of cholera outbreaks in individual countries in South-East Asia follows. The countries of the World Health Organization (WHO) SEARO (South-East Asia Region) region are discussed first, followed by discussions about the other countries in South-East Asia that do not fall within the purview of the WHO SEARO classification of the member countries of the region. Therefore, the chapter attempts to provide a comprehensive yet precise outline of the major cholera outbreaks that have occurred in the region over the years.

The seventh pandemic Vibrio cholerae O1 El Tor isolate in China has undergone genetic shifts

A total of 330 clinical Vibrio cholerae O1 serogroups from China dating between 1961 and 2010 were investigated. By phenotypic biotyping and genetic analysis, during the seventh pandemic of V. cholerae O1 in China, the isolates of hybrid biotype (mixed classical phenotypes) were present during the entire1961-2010 period, while El Tor genetic shifts appeared in 1992 and replaced the prototype El Tor from 2002 to 2010.

Sequence polymorphisms of rfbT among the Vibrio cholerae O1 strains in the Ogawa and Inaba serotype shifts

Background

Vibrio cholerae serogroup O1 has two major serotypes, Ogawa and Inaba, which may alternate among cholera epidemics. The rfbT gene is responsible for the conversion between the two serotypes. In this study, we surveyed the sequence variance of rfbT in the Ogawa and Inaba strains in China over a 48-year (1961-2008) period in which serotype shifts occurred among epidemic years.

Results

Various mutation events including single nucleotide, short fragment insertions/deletions and transposases insertions, were found in the rfbT gene of the Inaba strains. Ectopically introducing an intact rfbT could overcome the mutations by converting the Inaba serotype to the Ogawa serotype, suggesting the effects of these mutations on the function of RfbT. Characteristic rfbT mutations were recognized in the Inaba strains among Inaba serotype dominant epidemic years which were separate from the Ogawa dominant epidemics. Three distinguishable mutation sites in rfbT between the classical and the El Tor biotype strains were identified and could serve as biotype-specific biomarkers.

Conclusions

Our results provide a comprehensive picture of the rfbT gene mutations among the V. cholerae O1 strains in different epidemic periods, which could be further used as the tracing markers in clonality analysis and dissemination surveillance of the epidemic strains.

The role of socioeconomic status in longitudinal trends of cholera in Matlab, Bangladesh, 1993-2007

There has been little evidence of a decline in the global burden of cholera in recent years as the number of cholera cases reported to WHO continues to rise. Cholera remains a global threat to public health and a key indicator of lack of socioeconomic development. Overall socioeconomic development is the ultimate solution for control of cholera as evidenced in developed countries. However, most research has focused on cross-county comparisons so that the role of individual- or small area-level socioeconomic status (SES) in cholera dynamics has not been carefully studied. Reported cases of cholera in Matlab, Bangladesh have fluctuated greatly over time and epidemic outbreaks of cholera continue, most recently with the introduction of a new serotype into the region. The wealth of longitudinal data on the population of Matlab provides a unique opportunity to explore the impact of socioeconomic status and other demographic characteristics on the long-term temporal dynamics of cholera in the region. In this population-based study we examine which factors impact the initial number of cholera cases in a bari at the beginning of the 0139 epidemic and the factors impacting the number of cases over time. Cholera data were derived from the ICDDR,B health records and linked to socioeconomic and geographic data collected as part of the Matlab Health and Demographic Surveillance System. Longitudinal zero-inflated Poisson (ZIP) multilevel regression models are used to examine the impact of environmental and socio-demographic factors on cholera counts across baris. Results indicate that baris with a high socioeconomic status had lower initial rates of cholera at the beginning of the 0139 epidemic (γ₀₁ = −0.147, p = 0.041) and a higher probability of reporting no cholera cases (α₀₁ = 0.156, p = 0.061). Populations in baris characterized by low SES are more likely to experience higher cholera morbidity at the beginning of an epidemic than populations in high SES baris.

Cholera is a bacterial disease usually spread through contaminated water that causes severe diarrhea and dehydration. Modern sewage and water treatment have virtually eliminated cholera in industrialized countries but cholera is still present throughout much of SE Asia, Latin America and sub-Saharan Africa. One of the reasons cholera is still problematic is that genetically distinct forms of the bacteria (often called biotypes) have developed and spread rapidly because the population has no natural immunity to the new biotype. In Bangladesh, the 0139 biotype developed in 1993 and caused a large epidemic. Although it is widely accepted that poor conditions place people at risk for cholera, very few studies have examine what role low socioeconomic status plays in cholera risk, especially during a new epidemic of the disease. In this paper, we explore how local-level socioeconomic status, measured using assets, education and sanitation, affect the severity of the cholera outbreak experienced during the O139 epidemic in Matlab, Bangladesh. We believe our study highlights the importance of improving overall socioeconomic status, not just sanitation and water treatment, in controlling the spread of cholera.

Cholera outbreaks in the classical biotype era

In the Indian subcontinent description of a disease resembling cholera has been mentioned in Sushruta Samita, estimated to have been written between ~400 and 500 BC. It is however not clear whether the disease known today as cholera caused by Vibrio cholerae Vibrio cholerae O1 is the evolutionary progression of the ancient disease. The modern history of cholera began in 1817 when an explosive epidemic broke out in the Ganges River Delta region of Bengal. This was the first of the seven recorded cholera pandemics cholera pandemics that affected nearly the entire world and caused hundreds of thousands of deaths. The bacterium responsible for this human disease was first recognised during the fifth pandemic and was named V. cholerae which was grouped as O1, and was further differentiated into Classical and El Tor biotypes. It is now known that the fifth and the sixth pandemics were caused by the V. cholerae O1 of the Classical biotype Classical biotype and the seventh by the El Tor biotype El Tor biotype . The El Tor biotype of V. cholerae, which originated in Indonesia Indonesia and shortly thereafter began to spread in the early 1960s. Within the span of 50 years the El Tor biotype had invaded nearly the entire world, completely displacing the Classical biotype from all the countries except Bangladesh. What prompted the earlier pandemics to begin is not clearly understood, nor do we know how and why they ended. The success of the seventh pandemic clone over the pre-existing sixth pandemic strain remains largely an unsolved mystery. Why classical biotype eventually disappeared from the world remains to be explained. For nearly three decades (1963-1991) during the Seventh cholera pandemic seventh pandemic, cholera in Bangladesh has recorded a unique history of co-existence of Classical and El Tor biotypes of V. cholerae O1 as epidemic and endemic strain. This long co-existence has provided us with great opportunity to improve our understanding of the disease itself and answer some important questions.

Cholera

Cholera is an acute, secretory diarrhoea caused by infection with Vibrio cholerae of the O1 or O139 serogroup. It is endemic in more than 50 countries and also causes large epidemics. Since 1817, seven cholera pandemics have spread from Asia to much of the world. The seventh pandemic began in 1961 and affects 3-5 million people each year, killing 120,000. Although mild cholera can be indistinguishable from other diarrhoeal illnesses, the presentation of severe cholera is distinct, with pronounced diarrhoeal purging. Management of patients with cholera involves aggressive fluid replacement; effective therapy can decrease mortality from more than 50% to less than 0·2%. Antibiotic treatment decreases volume and duration of diarrhoea by 50% and is recommended for patients with moderate to severe dehydration. Prevention of cholera depends on access to safe water and sanitation. Two oral cholera vaccines are available and the most effective use of these in integrated prevention programmes is being actively assessed.