Evidence for a clonally different origin of the two cholera epidemics of 2001-2002 and 1980-1987 in South Africa

Genetic relatedness, virulence factors and antibiotics susceptibility pattern of Vibrio cholerae isolates from various regions during cholera outbreak in Tanzania

Background

Cholera continues to cause morbidity and mortality in developing countries, including Tanzania. Since August 2015, Tanzania Mainland has experienced cholera outbreaks affecting 26 regions and a 1.6% case fatality rate. The current study determined the virulence factors, genetic relatedness and antimicrobial susceptibility patterns of the Vibrio cholerae isolated from different regions in Tanzania.

Methods

A cross-sectional study that involved the genetic characterization of V. cholerae isolates from eleven regions in Tanzania was carried out. There were 99 V. cholerae isolates collected between January 2016 and December 2017. The study perfomed a Multi-locus Variable-number tandem-repeat analysis for genetic relatedness and Mismatch Amplification Mutation Analysis polymerase chain reaction for analyzing toxin genes. All the isolates were tested for antimicrobial susceptibility using the Kirby Bauer disk diffusion method. Data were generally analyzed using Microsoft excel, where genetic relatedness was analyzed using eBurst software v3.

Results

All isolates were V. cholerae O1. Ogawa was the most predominant 97(98%) serotype. Isolates were genetically related with a small genetic diversity and were positive for ctxA, tcpA El Tor virulence genes. All isolates (100%) were sensitive to doxycycline, trimethoprim-sulphamethoxazole, tetracycline, ceftriaxone, and chloramphenicol, while 87.8% were sensitive to ciprofloxacin. A high resistance rate (100%) was detected towards erythromycin, nalidixic acid, amoxicillin, and ampicillin.

Conclusion

The V.cholerae O1 serotypes Ogawa, El Tor variant predominantly caused cholera outbreaks in Tanzania with strains clonally related regardless of the place and time of the outbreak. Most of the isolates were susceptible to the antibiotic regimen currently used in Tanzania. The high resistance rate detected for the other common antibiotics calls for continuous antimicrobial susceptibility testing during outbreaks.

Characterisation of Vibrio cholerae isolates from the 2009, 2010 and 2016 cholera outbreaks in Lusaka province, Zambia

Introduction

In 2009 and 2010, more than 6,000 cholera cases were recorded during these outbreaks with more than 80% of cases recorded in Lusaka province. After a five-year break, in 2016 an outbreak occurred in Lusaka, causing more than 1,000 cases of cholera. This study will strengthen the epidemiological information on the changing characteristics of the cholera outbreaks, for treatment, prevention and control of the disease.

Methods

This was a laboratory-based descriptive cross-sectional study conducted at the University Teaching Hospital in Lusaka, Zambia. A total of 83 V. cholerae O1 isolates were characterised by biochemical testing, serotyping, antimicrobial susceptibility testing, and macrorestriction analysis using Pulsed-Field Gel Electrophoresis.

Results

Macrorestriction analysis of the isolates demonstrated high genetic diversity among the isolates with 16 different patterns. The largest pattern comprised 9 isolates while the smallest one had 1 isolate. 2009 and 2010 isolates were highly resistant to nalidixic acid and cotrimoxazole, but highly sensitive to azithromycin and ampicillin. Of the fifty-two isolates from the 2016 cholera outbreak, 90% (47) were sensitive to cotrimoxazole, 94% (49) to tetracycline, and 98% (51) to azithromycin, while 98% (51) were resistant to nalidixic acid and 31(60%) to ampicillin.

Conclusion

macrorestriction analysis demonstrated high genetic diversity among the V. cholerae O1 strains, suggesting that these isolates were probably not from a similar source. This study also revealed the emergence of multidrug resistance among the 2016 V. cholerae outbreak isolates but were susceptible to cotrimoxazole, tetracycline, and azithromycin, which can be used for treatment of the cholera cases.

Review of molecular subtyping methodologies used to investigate outbreaks due to multidrug-resistant enteric bacterial pathogens in sub-Saharan Africa

Background

In sub-Saharan Africa, molecular epidemiological investigation of outbreaks caused by antimicrobial-resistant enteric bacterial pathogens have mostly been described for Salmonella species, Vibrio cholerae, Shigella species and Escherichia coli. For these organisms, I reviewed all publications describing the use of molecular subtyping methodologies to investigate outbreaks caused by multidrug-resistant (MDR) enteric bacterial infections.

Objectives

To describe the use of molecular subtyping methodologies to investigate outbreaks caused by MDR enteric bacterial pathogens in sub-Saharan Africa and to describe the current status of molecular subtyping capabilities in the region.

Methods

A PubMed database literature search (English language only) was performed using the search strings: ‘Africa outbreak MDR’, ‘Africa outbreak multi’, ‘Africa outbreak multidrug’, ‘Africa outbreak multi drug’, ‘Africa outbreak resistance’, ‘Africa outbreak resistant’, ‘Africa outbreak drug’, ‘Africa outbreak antibiotic’, ‘Africa outbreak antimicrobial’. These search strings were used in combination with genus and species names of the organisms listed above. All results were included in the review.

Results

The year 1991 saw one of the first reports describing the use of molecular subtyping methodologies in sub-Saharan Africa; this included the use of plasmid profiling to characterise Salmonella Enteritidis. To date, several methodologies have been used; pulsed-field gel electrophoresis analysis and multilocus sequence typing have been the most commonly used methodologies. Investigations have particularly highlighted the emergence and spread of MDR clones; these include Salmonella Typhi H58 and Salmonella Typhimurium ST313 clones. In recent times, whole-genome sequencing (WGS) analysis approaches have increasingly been used.

Conclusion

Traditional molecular subtyping methodologies are still commonly used and still have their place in investigations; however, WGS approaches have increasingly been used and are slowly gaining a stronghold. African laboratories need to start adapting their molecular surveillance methodologies to include WGS, as it is foreseen that WGS analysis will eventually replace all traditional methodologies.

Retrospective Analysis of Serotype Switching of Vibrio cholerae O1 in a Cholera Endemic Region Shows It Is a Non-random Process

Genomic data generated from clinical Vibrio cholerae O1 isolates collected over a five year period in an area of Kolkata, India with seasonal cholera outbreaks allowed a detailed genetic analysis of serotype switching that occurred from Ogawa to Inaba and back to Ogawa. The change from Ogawa to Inaba resulted from mutational disruption of the methyltransferase encoded by the wbeT gene. Re-emergence of the Ogawa serotype was found to result either from expansion of an already existing Ogawa clade or reversion of the mutation in an Inaba clade. Our data suggests that such transitions are not random events but rather driven by as yet unidentified selection mechanisms based on differences in the structure of the O1 antigen or in the serotype-determining wbeT gene.

Cholera is a major health problem in many parts of the world causing seasonal outbreaks in endemic areas. Essentially only the O1 serogroup of Vibrio cholerae causes epidemic cholera. This serogroup has two immunologically distinguishable serotype variants called Ogawa and Inaba. The Inaba serotype is a consequence of a mutation in a single gene, wbeT, that in its intact form encodes for an enzyme that methylates the terminal perosamine sugar of the lipopolysaccharide side chain thus resulting in the Ogawa serotype. By careful examination over a five-year period of the genetic lineages of bacteria causing cholera in an endemic area we show data indicating that serotype switching is not a random process but is driven by selection pressures that have yet to be identified.

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.

Phenotypic and genetic characterization of Vibrio cholerae O1 isolated from various regions of Kenya between 2007 and 2010

INTRODUCTION

Cholera, a disease caused by Vibrio cholerae O1 and O139 remains an important public health problem globally. In the last decade, Kenya has experienced a steady increase of cholera cases. In 2009 alone, 11,769 cases were reported to the Ministry of Public Health and Sanitation. This study sought to describe the phenotypic characteristics of the isolated V. cholerae isolates.

METHODS

This was a laboratory based cross-sectional study that involved isolates from different cholera outbreaks. Seventy six Vibrio cholerae O1 strains from different geographical areas were used to represent 2007 to 2010 cholera epidemics in Kenya, and were characterized by serotyping, biotyping, polymerase chain r(PCR), pulsed-field gel electrophoresis (PFGE) and ribotyping along with antimicrobial susceptibility testing.

RESULTS

Seventy six Vibrio cholerae O1 strains from different geographical areas were used to represent 2007 to 2010 cholera epidemics in Kenya. Serotype Inaba was dominant (88.2%) compared to Ogawa. The isolates showed varying levels of antibiotic resistance ranging from 100% susceptible to tetracycline, doxycycline, ofloxacin, azithromycin, norfloxacin and ceftriaxone to 100% resistant to furazolidone, trimethoprim-sulfamethoxazole, polymyxin-B and streptomycin. The isolates were positive for ctxA, tcpA (El Tor), rtxC genes and were biotype El Tor variant harboring classical ctxB gene. All the isolates were classified as cholera toxin (CT) genotype 1 as they had mutation in the ctxB at positions 39 and 68. All the isolates had genetically similar NotI PFGE and BglI ribotype patterns. The absence of any observed variation is consistent with a clonal origin for all of the isolates.

CONCLUSION

Kenya experienced cholera numerous outbreak from 2007-2010. The clinical Vibrio cholerae O1 isolates from the recent cholera epidemic were serotypes Inaba and Ogawa, Inaba being the predominant serotype. The Vibrio cholerae O1 strains were biotype El Tor variants that produce cholera toxin B (ctx B) of the classical type and were positive for ctxA, tcpA El Tor and rtxC genes.

Cholera in coastal Africa: a systematic review of its heterogeneous environmental determinants

According to the "cholera paradigm," epidemiology of this prototypical waterborne disease is considered to be driven directly by climate-induced variations in coastal aquatic reservoirs of Vibrio cholerae. This systematic review on environmental determinants of cholera in coastal Africa shows that instead coastal epidemics constitute a minor part of the continental cholera burden. Most of coastal cholera foci are located near estuaries, lagoons, mangrove forests, and on islands. Yet outbreaks often originate in coastal cities, where cholera is more likely to be imported from distant areas. Cholera outbreaks also may intensify in densely populated slum quarters before spreading to adjacent regions. Frequent seasonality of cholera incidence appears driven by the rainfall-induced contamination of unprotected water sources through latrine overflow and sewage, as well as by the periodicity of human activities like fishing or traveling. Lulls in transmission periods of several years are repeatedly recorded even in high-risk coastal areas. To date, environmental studies have failed to demonstrate a perennial aquatic reservoir of toxigenic V. cholerae around the continent. Finally, applicability of the cholera paradigm therefore appears questionable in Africa, although available data remain limited. Thorough surveys with microbiological analyses of water samples and prospective genotyping of environmental and clinical strains of V. cholerae are needed to understand determinants of cholera in coastal Africa and better target prevention and control measures.