Waterborne cholera outbreak following Cyclone Aila in Sundarban area of West Bengal, India, 2009

Following Cyclone Aila, a block of Sundarban area, West Bengal, India, reported an increased number of diarrhoea cases at the end of May 2009. This study was performed to identify the agent and source of the outbreak as well as to propose control measures. The outbreak is described by time, place and person. A matched case-control study was conducted and rectal swabs and water specimens were collected. In total, 1076 probable case patients and 14 deaths (attack rate 44/10 000) were identified. Vibrio cholerae El Tor Ogawa was isolated from two of five probable case patients’ stool specimens. The outbreak started in the fourth week of May, with two peaks in the second and fourth weeks of June, and lasted until August 2009. Compared with controls, cases were more likely to drink non-chlorinated piped water [matched odds ratio (MOR) = 16, 95% CI 4.9-51; population attributable fraction 58%) and were less likely to drink chlorine-treated water (MOR = 0.06, 95% CI 0.02-0.18). Villagers broke the water pipelines near their houses for easy access to water. Piped water specimens and stored drinking water were positive for faecal contamination. Contaminated drinking water was the probable source of the cholera outbreak. Repairing the pipelines, chlorination at household level and educating villagers regarding the danger of breached water pipe connections controlled the outbreak.     

Emergence of Vibrio cholerae O1 Sequence Type 75, South Africa, 2018–2020

We describe the molecular epidemiology of cholera in South Africa during 2018–2020. Vibrio cholerae O1 sequence type (ST) 75 recently emerged and became more prevalent than the V. cholerae O1 biotype El Tor pandemic clone. ST75 isolates were found across large spatial and temporal distances, suggesting local ST75 spread.     

Seventh Pandemic Vibrio cholerae O1 Sublineages,Central African Republic

Four cholera outbreaks were reported in the Central African Republic during 1997–2016. We show that the outbreak isolates were Vibrio cholerae O1 serotype Inaba from 3 seventh pandemic El Tor sublineages originating from West Africa (sublineages T7 and T9) or the African Great Lakes Region (T10).     

Familial Aggregation of Vibrio cholerae-associated Infection in Matlab, Bangladesh

Vibrio cholerae is a major cause of diarrhoeal illness in endemic regions, such as Bangladesh. Understanding the factors that determine an individual''s susceptibility to infection due to V. cholerae may lead to improved prevention and control strategies. Increasing evidence suggests that human genetic factors affect the severity of V. cholerae-associated infection. This study, therefore, sought to characterize the heritable component of susceptibility to infection due to V. cholerae using the Matlab Health and Demographic Surveillance System database of the International Centre for Diarrhoeal Disease Research, Bangladesh. In total, 144 pedigrees that included a cholera patient and 341 pedigrees without a cholera patient were evaluated during 1 January–31 December 1992. The odds of the sibling of a patient being admitted with cholera were 7.67 times the odds of the sibling of an unaffected individual being admitted with cholera [95% confidence interval (CI) 2.40–24.5, p<0.001], after adjustment for gender, age, socioeconomic status, and hygiene practices. Although exposure to environmental reservoirs is essential in the epidemiology of cholera, household-specific factors, such as familial relatedness to an index case, may also be important determinants of risk of cholera. Further analysis of human genetic factors that contribute to susceptibility to cholera may be productive.Key words: Case-control studies, Cholera, Familial aggregation, Risk factors, Vibrio cholerae, Bangladesh     

Outbreak of Imported Seventh Pandemic Vibrio cholerae O1 El Tor,Algeria, 2018

After a lull of >20 years, Algeria experienced a cholera outbreak in 2018 that included 291 suspected cases. We found that outbreak isolates were Vibrio cholerae O1 serotype Ogawa from seventh pandemic El Tor sublineage AFR14, which corresponds to a new introduction of cholera into Africa from South Asia.     

Monitoring Water Sources for Environmental Reservoirs of Toxigenic Vibrio cholerae O1, Haiti

An epidemic of cholera infections was documented in Haiti for the first time in more than 100 years during October 2010. Cases have continued to occur, raising the question of whether the microorganism has established environmental reservoirs in Haiti. We monitored 14 environmental sites near the towns of Gressier and Leogane during April 2012–March 2013. Toxigenic Vibrio cholerae O1 El Tor biotype strains were isolated from 3 (1.7%) of 179 water samples; nontoxigenic O1 V. cholerae was isolated from an additional 3 samples. All samples containing V. cholerae O1 also contained non-O1 V. cholerae. V. cholerae O1 was isolated only when water temperatures were ≥31°C. Our data substantiate the presence of toxigenic V. cholerae O1 in the aquatic environment in Haiti. These isolations may reflect establishment of long-term environmental reservoirs in Haiti, which may complicate eradication of cholera from this coastal country.     

Genomic and Phenotypic Insights for Toxigenic Clinical Vibrio cholerae O141

Vibrio cholerae remains a major public health threat worldwide, causing millions of cholera cases each year. Although much is known about the evolution and pathogenicity of the O1/O139 serogroups of V. cholerae, information is lacking on the molecular epidemiology of non‒O1/O139 strains isolated from patients who have diarrheal illnesses. We performed whole-genome sequence analysis and in vivo infections to investigate characteristics of V. cholerae O141 isolated from sporadic diarrheal cases in 4 countries. The strains formed a distinct phylogenetic clade distinguishable from other serogroups and a unique multilocus sequence type 42, but interstrain variation suggests that O141 isolates are not clonal. These isolates encode virulence factors including cholera toxin and the toxin-coregulated pilus, as well as a type 3 secretion system. They had widely variable capacities for intestinal colonization in the infant mouse model. We propose that O141 isolates comprise a distinct clade of V. cholerae non‒O1/O139, and their continued surveillance is warranted.     

Investigation of a Cholera Outbreak in a Tea Garden of Sivasagar District of Assam

Background:

In late May 2012, Bagjan division of Borbam tea estate, of Sivasagar district of Assam was affected by an outbreak of acute watery diarrhea, subsequently confirmed as Vibrio cholerae O1.

Objectives:

Our objective is to investigate and control the acute diarrheal disease outbreak in Sivasagar district of Assam.

Materials and Methods:

A physician-epidemiologist-led team did rapid outbreak investigation to confirm the outbreak and instituted treatment and control measures. Quantitative data collection was done using standard schedule and qualitative data by using key informant interview schedule.

Results:

Spot mapping of cases was done along the garden residential lines. About 120 suspected cases were line listed; with 1:1.23 male: female ratio. Ages ranged from 3 to 70 years (median - 40.5 years). Attack rate was 4.79% with one death; case fatality rate was 0.83%. Open air defecation was practiced by 94.6%. Rectal swabs were positive for V. cholerae O1 (Ogawa). All the piped water samples were class IV unsatisfactory for domestic use.

Conclusions:

There is a need to improve water and sanitation facility in the tea garden lines along with implementation of a strengthened disease surveillance system through integrated disease surveillance project covering all tea estates.     

Comparative genomic analysis of two isolates of Vibrio cholerae O1 Ogawa El Tor isolated during outbreak in Mariupol in 2011

Cholera is a water-borne, severe enteric infection essentially caused by toxigenic strains of Vibrio cholera O1 and O139 serogroups. An outbreak of cholera was registered during May–July 2011 in Mariupol, Ukraine, with 33 cholera cases and 25 carriers of cholera. Following this outbreak, the toxigenic strain of V. cholerae 2011EL-301 was isolated from seawater in the recreation area of Taganrog city on the territory of Russia. The aim of our study was to understand genomic features of Mariupol isolates as well as to evaluate hypothesis about possible interconnection between the outbreak of cholera in Mariupol and the single case of isolation of V. cholerae from the Sea of Azov in Russia. Mariupol isolates were phenotypically characterized and subsequently subjected to whole genome sequencing procedure. Phylogenetic analysis based on high-quality SNPs of V. cholera O1 El Tor isolates of the 7th pandemic clade from different regions showed that clinical and environmental isolates from Mariupol outbreak were attributable to a unique phylogenetic clade within wave 3 of V. cholera O1 El Tor isolates and characterized by six clade-specific SNPs. Whereas Taganrog isolate belonged to distantly related clade which allows us to reject the hypothesis of transmission the outbreak strain of V. cholerae O1 from Ukraine to Russia in 2011. Mariupol isolates shared a common ancestor with Haiti\Nepal-4\India clade indicating that outbreak progenitor strain most likely originated in the South Asia region and later was introduced to Ukraine. Moreover, genomic data both based on hqSNPs and similarity of virulence-associated mobile genomic elements of Mariupol isolates suggests that environmental and clinical isolates are a part of joint outbreak which confirms the role of contaminated domestic sewage, as an element of the complex chain of infection spread during cholera outbreak. In general, the genome-wide comparative analysis of both genes and genomic regions of epidemiological importance indicates accessory of this isolates to ‘new’ clone of toxigenic multiple drug resistance atypical variant of V. cholerae O1 El Tor.     

Genomic Epidemiology of Vibrio cholerae O139, Zhejiang Province,China, 1994–2018

Cholera caused by Vibrio cholerae O139 was first reported in Bangladesh and India in 1992. To determine the genomic epidemiology and origins of O139 in China, we sequenced 104 O139 isolates collected from Zhejiang Province, China, during 1994–2018 and compared them with 57 O139 genomes from other countries in Asia. Most Zhejiang isolates fell into 3 clusters (C1–C3), which probably originated in India (C1) and Thailand (C2 and C3) during the early 1990s. Different clusters harbored different antimicrobial resistance genes and IncA/C plasmids. The integrative and conjugative elements carried by Zhejiang isolates were of a new type, differing from ICEVchInd4 and SXT^MO10 by single-nucleotide polymorphisms and presence of genes. Quinolone resistance–conferring mutations S85L in parC and S83I in gyrA occurred in 71.2% of the Zhejiang isolates. The ctxB copy number differed among the 3 clusters. Our findings provided new insights for prevention and control of O139 cholera .     

Is Vibrio fluvialis Emerging As a Pathogen with Epidemic Potential in Coastal Region of Eastern India Following Cyclone Aila?

An isolated area with diarrhoea epidemic was explored at Pakhirala village of the Sundarbans, a coastal region of South 24 Parganas district of West Bengal, eastern India. The Pakhirala village was surrounded by other villages affected by a similar epidemic. The affected villages experienced this epidemic following the cyclone Aila, which had hit the coastal region of the Sundarbans in eastern India. In Pakhirala, the situation was the worst. Within a span of six weeks (5 June–20 July 2009), 3,529 (91.2%) of 3,871 residents were affected by watery diarrhoea. Of all the cases (n=3,529), 918 (26%) were affected by moderate to severe diarrhoea. In other villages, 28,550 (70%) of the 40,786 people were affected; of them, 3,997 (14%) had moderate to severe watery diarrhoea. The attack rate and the severity of the cases were significantly higher in Pakhirala village compared to other affected villages. The laboratory results revealed that Vibrio fluvialis was the predominant pathogen in Pakhirala village (5 of 6 laboratory-confirmed organisms) whereas Vibrio cholerae O1 Ogawa was the predominant pathogen in other villages of Gosaba block (7 of 9 bacteriologically-confirmed organisms). This result indicates that V. fluvialis behaves more aggressively than V. cholerae O1 in an epidemic situation with a higher attack rate and a different clinical picture. An in-depth study is required to explore its pathogenicity in detail, geographical distribution, and possible control measures, including development of specific vaccine preparation and determination of its efficacy.Key words: Diarrhoea, Cyclone, Disasters, Natural, Vibrio cholerae, Vibrio fluvialis, India     

Dynamics in genome evolution of Vibrio cholerae

Vibrio cholerae, the etiological agent of the acute secretary diarrheal disease cholera, is still a major public health concern in developing countries. In former centuries cholera was a permanent threat even to the highly developed populations of Europe, North America, and the northern part of Asia. Extensive studies on the cholera bug over more than a century have made significant advances in our understanding of the disease and ways of treating patients.V. cholerae has more than 200 serogroups, but only few serogroups have caused disease on a worldwide scale. Until the present, the evolutionary relationship of these pandemic causing serogroups was not clear. In the last decades, we have witnessed a shift involving genetically and phenotypically varied pandemic clones of V. cholerae in Asia and Africa. The exponential knowledge on the genome of several representatives V. cholerae strains has been used to identify and analyze the key determinants for rapid evolution of cholera pathogen. Recent comparative genomic studies have identified the presence of various integrative mobile genetic elements (IMGEs) in V. cholerae genome, which can be used as a marker of differentiation of all seventh pandemic clones with very similar core genome. This review attempts to bring together some of the important researches in recent times that have contributed towards understanding the genetics, epidemiology and evolution of toxigenic V. cholerae strains.     

Understanding the Cholera Epidemic, Haiti

After onset of a cholera epidemic in Haiti in mid-October 2010, a team of researchers from France and Haiti implemented field investigations and built a database of daily cases to facilitate identification of communes most affected. Several models were used to identify spatiotemporal clusters, assess relative risk associated with the epidemic’s spread, and investigate causes of its rapid expansion in Artibonite Department. Spatiotemporal analyses highlighted 5 significant clusters (p<0.001): 1 near Mirebalais (October 16–19) next to a United Nations camp with deficient sanitation, 1 along the Artibonite River (October 20–28), and 3 caused by the centrifugal epidemic spread during November. The regression model indicated that cholera more severely affected communes in the coastal plain (risk ratio 4.91) along the Artibonite River downstream of Mirebalais (risk ratio 4.60). Our findings strongly suggest that contamination of the Artibonite and 1 of its tributaries downstream from a military camp triggered the epidemic.On October 21, 2010, the Haitian Ministry of Public Health and Population (MSPP) reported a cholera epidemic caused by Vibrio cholerae O1, serotype Ogawa, biotype El Tor (1). This epidemic was surprising as no cholera outbreak had been reported in Haiti for more than a century (1,2). Numerous media rapidly related the epidemic to the deadly earthquake that Haiti had experienced 9 months earlier. However, simultaneously, a rumor held recently incoming Nepalese soldiers responsible for importing cholera, along with accusations of illegal dumping of waste tank contents (3). A cholera outbreak was indeed reported in Nepal’s capital city of Kathmandu on September 23, 2010, shortly before troops left for Haiti (4,5). Two hypotheses then emerged to explain cholera in Haiti.Some researchers posited the transmission of an environmental strain to humans (6). Reasoning by analogy with cholera epidemiology in South Asia, they hypothesized that weather conditions, i.e., the La Niña phenomenon, might have promoted the growth of V. cholerae in its environmental reservoir (6). The second hypothesis suggested importation of the disease from a cholera-endemic country. The sequencing of 2 isolates of V. cholerae supported this second hypothesis by establishing an exogenous origin, probably from southern Asia or eastern Africa (7). Responding to a request from Haitian authorities to the French Embassy for the support of epidemiologists, we conducted a joint French–Haitian investigation during November 7–November 27, 2010, to clarify the source of the epidemic and its unusual dynamic.     

Resistance to antimicrobial agents of Vibrio cholerae El Tor strains isolated during the fourth cholera epidemic in the United Republic of Tanzania

Isolates of Vibrio cholerae obtained immediately after the outbreak of the fourth recorded epidemic of cholera in the United Republic of Tanzania were sensitive to tetracycline, but after five months of its extensive therapeutic and prophylactic use, 76% of the isolates were observed to be resistant to this and other antimicrobial agents. The appearance of resistance was found to be due to the rapid spread of antibiotic resistance plasmids belonging to the C incompatibility complex. Although most plasmid incompatibility groups have been shown to be unstable in V. cholerae, the strains found in the present epidemic seem to carry a plasmid belonging to one of the few relatively stable groups. These findings emphasize the importance of monitoring any emergence of bacterial resistance that may occur when mass prophylaxis programmes are in operation and also the importance of determining the genetic basis of the resistance mechanism.     

Genomic epidemiological investigation of a Streptococcus suis outbreak in Guangxi,China, 2016

In June 2016, a Streptococcus suis outbreak occurred in Guangxi, China. We determined the genetic characteristics of six clinically isolated strains by serotyping, PCR, and whole-genome sequencing, performing genome epidemiology analysis on these and 961 public available S. suis genomes. We also classified the first sequence type ST665 human case. Sporadic and outbreak cases were distinguished by whole-genome sequencing and phylogenomics. This approach could help to prevent and control S. suis epidemics in Guangxi and the wider region.     

Vibrio cholerae O1 Ogawa El Tor strains with the ctxB7 allele driving cholera outbreaks in south-western India in 2012

Cholera has been a recurrent epidemic disease in human populations for the past 200 years. We present herein a comparative characterization of clinical Vibrio cholerae strains isolated from two consecutive cholera outbreaks in 2012 and associated environmental strains from western India. The clinical and toxigenic environmental isolates were identified as hybrid V. cholerae O1, serotype Ogawa, biotype El Tor carrying the variant ctxB7 allele. Partial sequences of SXT integrase from the isolates revealed 100% identity to ICEVchInd5 (Sevagram, India, 1994) and VC1786ICE (Haiti, 2013). The full clonal relationship of the strains established by RAPD, Box PCR, ERIC PCR and MLST (pyrH, recA and rpoA) analyses, and the short time between the two outbreaks, strongly supported that both outbreaks were due to a single strain. The study corroborated that faecal contamination of the potable water supply was the main reason for the first outbreak, which further spread to other areas and resulted in the second outbreak. The study concluded that the circulating El Tor variant strains of epidemic potential in the region can be a serious concern in the future.     

Evolution,distribution and genetics of atypical Vibrio cholerae – A review

Vibrio cholerae is the etiological agent of cholera, a severe diarrheal disease, which can occur as either an epidemic or sporadic disease. Cholera pandemic-causing V. cholerae O1 and O139 serogroups originated from the Indian subcontinent and spread globally and millions of lives are lost each year, mainly in developing and underdeveloped countries due to this disease. V. cholerae O1 is further classified as classical and El Tor biotype which can produce biotype specific cholera toxin (CT). Since 1961, the current seventh pandemic El Tor strains replaced the sixth pandemic strains resulting in the classical biotype strain that produces classical CT. The ongoing evolution of Atypical El Tor V. cholerae srains encoding classical CT is of global concern. The severity in the pathophysiology of these Atypical El Tor strains is significantly higher than El Tor or classical strains. Pathogenesis of V. cholerae is a complex process that involves coordinated expression of different sets of virulence-associated genes to cause disease. We are yet to understand the complete virulence profile of V. cholerae, including direct and indirect expression of genes involved in its survival and stress adaptation in the host. In recent years, whole genome sequencing has paved the way for better understanding of the evolution and strain distribution, outbreak identification and pathogen surveillance for the implementation of direct infection control measures in the clinic against many infectious pathogens including V. cholerae. This review provides a synopsis of recent studies that have contributed to the understanding of the evolution, distribution and genetics of the seventh pandemic Atypical El Tor V. cholerae strains.     

Cholera in Bahrain: epidemiological characteristics of an outbreak

In the period 10 August 1978-23 January 1979, 913 culture-confirmed cases of cholera caused by Vibrio cholerae, biotype El Tor, serotype Ogawa, occurred in Bahrain. After discovery of the initial cases, others occurred sporadically, and the incidence reached a peak of 25-35 cases per day during the seventh week of the outbreak (16-22 September). The overall attack rate (27 per 10 000) was low and the outbreak subsided without mass immunization campaigns or rigorous border control of persons and imports. Investigation of 746 culture-confirmed cases that occurred in the period 10 August—13 October 1978, showed that cases occurred throughout most areas of the country and mainly affected infants, young children, and adult working-age males. Symptoms were very mild; fewer than 20% of patients required specific rehydration therapy. The highest attack rate (84 per 10 000) occurred in infants less than 1 year of age. No common vehicle or mode of transmission was identified. A matched-pair study of 35 cases and controls showed that adult cases were more likely than controls to have consumed food or beverage outside of the home before becoming ill. V. cholerae was isolated from stored drinking water in the houses of 8 cases but not from numerous samples of food and tap-water. It was presumed that cholera transmission occurred through a complex interaction of mild and asymptomatically infected persons with food, water, and the environment.     

Multiplex Real-time Polymerase Chain Reaction Assays for Simultaneous Detection of Vibrio cholerae,Vibrio parahaemolyticus,and Vibrio vulnificus

ObjectivesA multiplex real-time polymerase chain reaction (RT-PCR) method was developed for the identification of three Vibrio species: Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus.MethodsSpecific primers and probes targeting the hlyA, tlh, and vvhA genes were selected and used for multiplex real-time PCR to confirm the identification of V. cholerae, V. parahaemolyticus, and V. vulnificus, respectively. This method was applied to screen Vibrio species from environmental samples and combining it with a culture-based method, its effectiveness was evaluated in comparison with culture-based methods alone.ResultsSpecific PCR fragments were obtained from isolates belonging to the target species, indicating a high specificity of this multiplex real-time PCR. No cross-reactivity with the assay was observed between the tested bacteria. The sensitivity of the multiplex real-time PCR was found to have a lower limit of 10⁴ colony-forming units/reaction for all three Vibrio species. The combination strategy raised the isolation ratio of all three Vibrio species 1.26- to 2.75-fold.ConclusionThis assay provides a rapid, sensitive, and specific technique to detect these three Vibrio species in the environment.     

Randomized Controlled Trial of Hospital-Based Hygiene and Water Treatment Intervention (CHoBI7) to Reduce Cholera

The risk for cholera infection is >100 times higher for household contacts of cholera patients during the week after the index patient seeks hospital care than it is for the general population. To initiate a standard of care for this high-risk population, we developed Cholera-Hospital-Based-Intervention-for-7-Days (CHoBI7), which promotes hand washing with soap and treatment of water. To test CHoBI7, we conducted a randomized controlled trial among 219 intervention household contacts of 82 cholera patients and 220 control contacts of 83 cholera patients in Dhaka, Bangladesh, during 2013–2014. Intervention contacts had significantly fewer symptomatic Vibrio cholerae infections than did control contacts and 47% fewer overall V. cholerae infections. Intervention households had no stored drinking water with V. cholerae and 14 times higher odds of hand washing with soap at key events during structured observation on surveillance days 5, 6, or 7. CHoBI7 presents a promising approach for controlling cholera among highly susceptible household contacts of cholera patients.