Production, characterization, and application of monoclonal antibodies to Vibrio cholerae O139 synonym Bengal

Characteristics of Rotavirus, ETEC, and Vibrio Cholerae Among Under 2-year Children Attending an Urban Diarrheal Disease Hospital in Bangladesh

Background

Information on comparative clinical and host characteristics of under-2 children with watery diarrhea caused by rotavirus, Enterotoxigenic Escherichia coli (ETEC), and Vibrio cholerae as single pathogens is lacking. We sought to investigate the sociodemographic, clinical, and host characteristics of under-2 children hospitalized due to these pathogens.

Methodology

We conducted a hospital-based case-control study using the icddr,b Diarrheal Diseases Surveillance System. Children of either sex, <2 years with diarrhea, who attended the hospital during 2014 to 2018, constituted the study population. Stool specimens having a single pathogen like rotavirus, ETEC, or Vibrio cholerae constituted the cases and stool specimens having no detectable common enteropathogens comprised the controls. Multinomial logistic regression analysis was done where control was the reference group.

Results

A total of 14 889 patients were enrolled, 6939 of whom were under-2 children, and 5245 (76%) constituted our study population. Among them 48% (n = 2532), 3% (n = 148) and 1% (n = 49) had rotavirus, ETEC, and Vibrio cholera, respectively. A control group (diarrhea without these 3 or Shigella, Salmonella, Aeromonas) accounted for 48% (n = 2516). In multinomial regression model, children with rotavirus (adjusted odds ratio [aOR], 1.36; 95% confidence interval [95% CI], 1.19-1.55) less often presented with dehydrating diarrhea compared to those with ETEC (aOR, 1.54; 95% CI, 1.05-2.26) and cholera (aOR, 2.25; 95% CI, 1.11-4.57). Rotavirus diarrhea was associated (aOR, 1.25; 95% CI, 1.07-1.46) with those who received antimicrobials prior to hospital admission and protectively associated with drinking tap water (aOR, 0.84; 95% CI, 0.73-0.95); however, ETEC diarrhea had protective association (aOR, 0.62; 95% CI, 0.43-0.92) with children who received antimicrobials prior to hospital admission and was associated with drinking tap water (aOR, 1.78; 95% CI, 1.19-2.66). Use of intravenous fluid was associated with cholera (aOR, 10.36; 95% CI, 4.85-22.16) and had protective association with rotavirus episodes (aOR, 0.64; 95% CI, 0.45-0.91).

Conclusions

Clinical presentations and host characteristics of rotavirus, ETEC, and Vibrio cholerae diarrhea differed from each other and the information may be helpful for clinicians for better understanding and proper management of these children.

Unmasking herd protection by an oral cholera vaccine in a cluster-randomized trial

Background

Several studies have shown that inactivated, whole-cell oral cholera vaccines (OCVs) confer both direct protection on vaccinees and herd protection on populations. Because our earlier cluster-randomized effectiveness trial (CRT) in urban Bangladesh failed to detect OCV herd protection, we reanalysed the trial to assess whether herd effects were masked in our original analysis.

Methods

A total of 267 270 persons were randomized to 90 approximately equal-sized clusters. In 60 clusters persons aged 1 year and older were eligible to receive OCV and in 30 clusters persons received no intervention and served as controls. We analysed OCV protection against severely dehydrating cholera for the entire clusters, as in our original analysis, and for subclusters consisting of residents of innermost households. We hypothesized that if OCV herd protection was attenuated by cholera transmission into the clusters from the outside in this densely populated setting, herd protection would be most evident in the innermost households.

Results

During 2 years of follow-up of all residents of the clusters, total protection (protection of OCV recipients relative to control residents) was 58% [95% confidence interval (CI): 43%, 70%; P<0.0001], indirect protection (protection of non-OCV recipients in OCV clusters relative to control participants) was 16% (95% CI: –20%, 41%; P=0.35) and overall OCV protection (protection of all residents in the OCV clusters relative to control residents) was 46% (95% CI: 30%, 59%; P<0.0001). Analyses of the inner 75% and 50% households of the clusters showed similar findings. However, total protection was 75% (95% CI: 50%, 87%, P<0.0001), indirect protection 52% (95% CI: –9%, 79%; P=0.08) and overall protection 72% (95% CI: 49%, 84%; P<0.0001) for the innermost 25% households.

Conclusion

Consistent with past studies, substantial OCV herd protective effects were identified, but were unmasked only by analysing innermost households of the clusters. Caution is needed in defining clusters for analysis of vaccine herd effects in CRTs of vaccines.

Assessment of disease specific immune responses in enteric diseases using dried blood spot (DBS)

BACKGROUND

Blood collection, transportation and storage remain a problem in countries where infrastructure, laboratory facilities and skilled manpower are scarce. This limits evaluation of immune responses in natural infections and vaccination in field studies. We developed methods to measure antigen specific antibody responses using dried blood spot (DBS) in cholera, ETEC and typhoid fever patients as well as recipients of oral cholera vaccine (OCV).

METHODOLOGY/PRINCIPLE FINDINGS

We processed heparinized blood for preparing DBS and plasma specimens from patients with, cholera, ETEC and typhoid as well as OCV recipients. We optimized the conventional vibriocidal method to measure vibriocidal antibody response in DBS eluates. We measured responses in DBS samples and plasma (range of titer of 5 to 10240). Vibriocidal titer showed strong agreement between DBS eluates and plasma in cholera patients (ICC = 0.9) and in OCV recipients (ICC = 0.8) using the Bland-Altman analysis and a positive correlation was seen (r = 0.7, p = 0.02 and r = 0.6, p = 0.006, respectively). We observed a strong agreement of lipopolysaccharide (LPS) and cholera toxin B (CTB)-specific antibody responses between DBS eluates and plasma in cholera patients and OCV recipients. We also found agreement of heat labile toxin B (LTB) and membrane protein (MP)-specific antibody responses in DBS eluates and plasma specimen of ETEC and typhoid patients respectively.

CONCLUSION

Our results demonstrate that dried blood specimens can be used as an alternate method for preservation of samples to measure antibody responses in enteric diseases and vaccine trials and can be applied to assessment of responses in humanitarian crisis and other adverse field settings.

Cognate T and B cell interaction and association of follicular helper T cells with B cell responses in Vibrio cholerae O1 infected Bangladeshi adults

Vibrio cholerae O1 can cause life threatening diarrheal disease if left untreated. T cells can play critical roles in inducing B cell mediated immunity. As the mechanism of T cell dependent B cell maturation is not well established, we hypothesized that a specific population of T (follicular helper T, Tfh) cells, are involved in B cell maturation following cholera. We found flowcytometrically that V. cholerae infection induces significant increases in circulating Tfh cells expressing B cell maturation associated protein CD40L early in disease. The increased Tfh cells expressing CD40L recognize cholera toxin most prominently, with lessened responses to V. cholerae membrane preparation (MP) and V. cholerae cytolysin (VCC). We further showed that early induction of Tfh cells and CD40L was associated with later memory B cell responses to same antigens. Lastly, we demonstrated in vitro that Tfh cells isolated after cholera can stimulate class switching of co-cultured, isolated B cells from patients with cholera, leading to production of the more durable IgG antibody isotype colorimetrically. These studies were conducted on circulating Tfh cells; future studies will be directed at examining role of Tfh cells during cholera directly in gut mucosa of biopsied samples, at the single cell level if feasible.

Efficacy of a single-dose regimen of inactivated whole-cell oral cholera vaccine: results from 2 years of follow-up of a randomised trial

BACKGROUND

A single-dose regimen of inactivated whole-cell oral cholera vaccine (OCV) is attractive because it reduces logistical challenges for vaccination and could enable more people to be vaccinated. Previously, we reported the efficacy of a single dose of an OCV vaccine during the 6 months following dosing. Herein, we report the results of 2 years of follow-up.

METHODS

In this placebo-controlled, double-blind trial done in Dhaka, Bangladesh, individuals aged 1 year or older with no history of receipt of OCV were randomly assigned to receive a single dose of inactivated OCV or oral placebo. The primary endpoint was a confirmed episode of non-bloody diarrhoea for which the onset was at least 7 days after dosing and a faecal culture was positive for Vibrio cholerae O1 or O139. Passive surveillance for diarrhoea was done in 13 hospitals or major clinics located in or near the study area for 2 years after the last administered dose. We assessed the protective efficacy of the OCV against culture-confirmed cholera occurring 7-730 days after dosing with both crude and multivariable per-protocol analyses. This trial is registered at ClinicalTrials.gov, number NCT02027207.

FINDINGS

Between Jan 10, 2014, and Feb 4, 2014, 205 513 people were randomly assigned to receive either vaccine or placebo, of whom 204 700 (102 552 vaccine recipients and 102 148 placebo recipients) were included in the per-protocol analysis. 287 first episodes of cholera (109 among vaccine recipients and 178 among placebo recipients) were detected during the 2-year follow-up; 138 of these episodes (46 in vaccine recipients and 92 in placebo recipients) were associated with severe dehydration. The overall incidence rates of initial cholera episodes were 0·22 (95% CI 0·18 to 0·27) per 100 000 person-days in vaccine recipients versus 0·36 (0·31 to 0·42) per 100 000 person-days in placebo recipients (adjusted protective efficacy 39%, 95% CI 23 to 52). The overall incidence of severe cholera was 0·09 (0·07 to 0·12) per 100 000 person-days versus 0·19 (0·15 to 0·23; adjusted protective efficacy 50%, 29 to 65). Vaccine protective efficacy was 52% (8 to 75) against all cholera episodes and 71% (27 to 88) against severe cholera episodes in participants aged 5 years to younger than 15 years. For participants aged 15 years or older, vaccine protective efficacy was 59% (42 to 71) against all cholera episodes and 59% (35 to 74) against severe cholera. The protection in the older age groups was sustained throughout the 2-year follow-up. In participants younger than 5 years, the vaccine did not show protection against either all cholera episodes (protective efficacy -13%, -68 to 25) or severe cholera episodes (-44%, -220 to 35).

INTERPRETATION

A single dose of the inactivated whole-cell OCV offered protection to older children and adults that was sustained for at least 2 years. The absence of protection of young children might reflect a lesser degree of pre-existing natural immunity in this age group.

FUNDING

Bill & Melinda Gates Foundation to the International Vaccine Institute.

Development of a new dipstick (Cholkit) for rapid detection of Vibrio cholerae O1 in acute watery diarrheal stools

Recognizing cholera cases early, especially in the initial phase of an outbreak and in areas where cholera has not previously circulated, is a high public health priority. Laboratory capacity in such settings is often limited. To address this, we have developed a rapid diagnostic test (RDT) termed Cholkit that is based on an immunochromatographic lateral flow assay for the diagnosis of cholera cases using stool. Cholkit contains a monoclonal antibody (ICL-33) to the O-specific polysaccharide (OSP) component of V. cholerae O1 lipopolysaccharide, and recognizes both Inaba and Ogawa serotypes. We tested the Cholkit dipstick using fresh stool specimens of 76 adults and children presenting with acute watery diarrhea at the icddr,b hospital in Dhaka, Bangladesh. We compared Cholkit’s performance with those of microbial culture, PCR (targeting the rfb and ctxA genes of V. cholerae) and the commercially available RDT, Crystal VC (Span Diagnostics; Surat, India). We found that all stool specimens with a positive culture for V. cholerae O1 (n = 19) were positive by Cholkit as well as Crystal VC. We then used Bayesian latent class modeling to estimate the sensitivity and specificity of each diagnostic assay. The sensitivity of Cholkit, microbiological culture, PCR and Crystal VC was 98% (95% CI: 88–100), 71% (95% CI: 59–81), 74% (95% CI: 59–86) and 98% (95% CI: 88–100), respectively. The specificity for V. cholerae O1 was 97% (95% CI: 89–100), 100%, 97% (95% CI: 93–99) and 98% (95% CI: 92–100), respectively. Of note, two Crystal VC dipsticks were positive for V. cholerae O139 but negative by culture and PCR in this area without known circulating epidemic V. cholerae O139. In conclusion, the Cholkit dipstick is simple to use, requires no dedicated laboratory capacity, and has a sensitivity and specificity for V. cholerae O1 of 98% and 97%, respectively. Cholkit warrants further evaluation in other settings.

Cholera is a severely dehydrating diarrheal disease that can lead to death if remains untreated. The incidence of case fatality is higher at the beginning of the outbreak. Diagnosis of cholera in the early stage of outbreak is a high public health priority. Although countries facing complex emergencies are more vulnerable to cholera outbreak, laboratory capacity in such settings is usually limited. To address this, here we report the development of a rapid diagnostic test (RDT) termed Cholkit for the diagnosis of cholera cases using stool and the assessment of its performance with those of microbial culture, PCR and Crystal VC assay, a commercially available dipstick using a latent class modeling approach.

Resistance Pattern and Molecular Characterization of Enterotoxigenic Escherichia coli (ETEC) Strains Isolated in Bangladesh

Background

Enterotoxigenic Escherichia coli (ETEC) is a common cause of bacterial infection leading to acute watery diarrhea in infants and young children as well as in travellers to ETEC endemic countries. Ciprofloxacin is a broad-spectrum antimicrobial agent nowadays used for the treatment of diarrhea. This study aimed to characterize ciprofloxacin resistant ETEC strains isolated from diarrheal patients in Bangladesh.

Methods

A total of 8580 stool specimens from diarrheal patients attending the icddr,b Dhaka hospital was screened for ETEC between 2005 and 2009. PCR and Ganglioside GM1- Enzyme Linked Immuno sorbent Assay (ELISA) was used for detection of Heat labile (LT) and Heat stable (ST) toxins of ETEC. Antimicrobial susceptibilities for commonly used antibiotics and the minimum inhibitory concentration (MIC) of nalidixic acid, ciprofloxacin and azithromycin were examined. DNA sequencing of representative ciprofloxacin resistant strains was performed to analyze mutations of the quinolone resistance-determining region of gyrA, gyrB, parC and parE. PCR was used for the detection of qnr, a plasmid mediated ciprofloxacin resistance gene. Clonal variations among ciprofloxacin resistant (Cip^R) and ciprofloxacin susceptible (Cip^S) strains were determined by Pulsed-field gel electrophoresis (PFGE).

Results

Among 1067 (12%) ETEC isolates identified, 42% produced LT/ST, 28% ST and 30% LT alone. Forty nine percent (n = 523) of the ETEC strains expressed one or more of the 13 tested colonization factors (CFs) as determined by dot blot immunoassay. Antibiotic resistance of the ETEC strains was observed as follows: ampicillin 66%, azithromycin 27%, ciprofloxacin 27%, ceftriazone 13%, cotrimaxazole 46%, doxycycline 44%, erythromycin 96%, nalidixic acid 83%, norfloxacin 27%, streptomycin 48% and tetracycline 42%. Resistance to ciprofloxacin increased from 13% in 2005 to 34% in 2009. None of the strains was resistant to mecillinam. The MIC of the nalidixic acid and ciprofloxacin of representative Cip^R strains were 256 μg/ml and 32μg/ml respectively. A single mutation (Ser⁸³-Leu) in gyrA was observed in the nalidixic acid resistant ETEC strains. In contrast, double mutation in gyrA (Ser⁸³-Leu, Asp⁸⁷-Asn) and a single mutation in parC (Glu⁸⁴-Ly) were found in ciprofloxacin resistant strains. Mutation of gyrB was not found in either the nalidixic acid or ciprofloxacin resistant strains. None of the ciprofloxacin resistant strains was found to be positive for the qnr gene. Diverse clones were identified from all ciprofloxacin resistant strains by PFGE analysis in both CF positive and CF negative ETEC strains.

Conclusion

Emergence of ciprofloxacin resistant ETEC strains results in a major challenge in current treatment strategies of ETEC diarrhea.

Efficacy of a Single-Dose, Inactivated Oral Cholera Vaccine in Bangladesh

BACKGROUND

A single-dose regimen of the current killed oral cholera vaccines that have been prequalified by the World Health Organization would make them more attractive for use against endemic and epidemic cholera. We conducted an efficacy trial of a single dose of the killed oral cholera vaccine Shanchol, which is currently given in a two-dose schedule, in an urban area in which cholera is highly endemic.

METHODS

Nonpregnant residents of Dhaka, Bangladesh, who were 1 year of age or older were randomly assigned to receive a single dose of oral cholera vaccine or oral placebo. The primary outcome was vaccine protective efficacy against culture-confirmed cholera occurring 7 to 180 days after dosing. Prespecified secondary outcomes included protective efficacy against severely dehydrating culture-confirmed cholera during the same interval, against cholera and severe cholera occurring 7 to 90 versus 91 to 180 days after dosing, and against cholera and severe cholera according to age at baseline.

RESULTS

A total of 101 episodes of cholera, 37 associated with severe dehydration, were detected among the 204,700 persons who received one dose of vaccine or placebo. The vaccine protective efficacy was 40% (95% confidence interval [CI], 11 to 60%; 0.37 cases per 1000 vaccine recipients vs. 0.62 cases per 1000 placebo recipients) against all cholera episodes, 63% (95% CI, 24 to 82%; 0.10 vs. 0.26 cases per 1000 recipients) against severely dehydrating cholera episodes, and 63% (95% CI, -39 to 90%), 56% (95% CI, 16 to 77%), and 16% (95% CI, -49% to 53%) against all cholera episodes among persons vaccinated at the age of 5 to 14 years, 15 or more years, and 1 to 4 years, respectively, although the differences according to age were not significant (P=0.25). Adverse events occurred at similar frequencies in the two groups.

CONCLUSIONS

A single dose of the oral cholera vaccine was efficacious in older children (≥5 years of age) and in adults in a setting with a high level of cholera endemicity. (Funded by the Bill and Melinda Gates Foundation and others; ClinicalTrials.gov number, NCT02027207.).

Vibrio cholerae Serogroup O139: Isolation from Cholera Patients and Asymptomatic Household Family Members in Bangladesh between 2013 and 2014

Background

Cholera is endemic in Bangladesh, with outbreaks reported annually. Currently, the majority of epidemic cholera reported globally is El Tor biotype Vibrio cholerae isolates of the serogroup O1. However, in Bangladesh, outbreaks attributed to V. cholerae serogroup O139 isolates, which fall within the same phylogenetic lineage as the O1 serogroup isolates, were seen between 1992 and 1993 and in 2002 to 2005. Since then, V. cholerae serogroup O139 has only been sporadically isolated in Bangladesh and is now rarely isolated elsewhere.

Methods

Here, we present case histories of four cholera patients infected with V. cholerae serogroup O139 in 2013 and 2014 in Bangladesh. We comprehensively typed these isolates using conventional approaches, as well as by whole genome sequencing. Phenotypic typing and PCR confirmed all four isolates belonging to the O139 serogroup.

Findings

Whole genome sequencing revealed that three of the isolates were phylogenetically closely related to previously sequenced El Tor biotype, pandemic 7, toxigenic V. cholerae O139 isolates originating from Bangladesh and elsewhere. The fourth isolate was a non-toxigenic V. cholerae that, by conventional approaches, typed as O139 serogroup but was genetically divergent from previously sequenced pandemic 7 V. cholerae lineages belonging to the O139 or O1 serogroups.

Conclusion

These results suggest that previously observed lineages of V. cholerae O139 persist in Bangladesh and can cause clinical disease and that a novel disease-causing non-toxigenic O139 isolate also occurs.

Vibrio cholerae serogroup O1 is thought to be the sole causative agent for cholera in Bangladesh and most of the high risk developing countries. Whilst historically Vibrio cholerae serogroup O139 has been seen to cause sporadic disease, the overall numbers of reported O139 clinical cases are low, with none reported in Bangladesh since 2005. Here we report four patients suffering from cholera attributed to serogroup O139 V. cholerae. Cases 1 and 2 were symptomatic (isolated strains 1, 2), and cases 3 and 4 were asymptomatic (isolated strains 3, 4). All cases were from urban Dhaka and represented a range of age groups. Cases 2–4 presented with no sign of dehydration whereas case 1 showed some signs of dehydration. Phenotypic and whole genome sequence data indicates that one of the four O139 V. cholerae isolates represents a novel O139 subtype. Since natural infection with V. cholerae O1 or vaccination with currently available licensed cholera vaccines (e.g., Dukoral) provides little protection against O139, we conclude that V. cholerae O139 remains in circulation and is still causing a low incidence of cholera. Therefore, further studies looking at the significance of these isolates towards the total burden of cholera in Bangladesh is warranted, including clinical evaluation, genome sequencing and immunobiochemistry.

Bacterial shedding in household contacts of cholera patients in Dhaka, Bangladesh

Multiple Vibrio cholerae infections within the same household are common. Household contacts of patients with cholera were observed with daily clinical assessments and collection of rectal swab cultures for nine days after presentation of the index case. During the follow-up period, 71 (24%) of 294 household contacts developed a positive V. cholerae rectal swab, signifying bacterial shedding. The average length of bacterial shedding was 2.0 days (95% confidence interval 1.7-2.4). However, 16 (5%) of 294 contacts shed V. cholerae for ≥ 4 days. In a multivariate analysis, malnutrition was predictive of long-term shedding (odds ratio = 1.4, 95% confidence interval = 1.3-13, P = 0.02). High rates of V. cholerae infection and bacterial shedding among household contacts of cholera patients represent an opportunity for intervention to reduce V. cholerae transmission.

Cholera Outbreaks in Urban Bangladesh In 2011

BACKGROUND

In 2011, a multidisciplinary team investigated two diarrhoea outbreaks affecting urban Bangladeshi communities from the districts of Bogra and Kishorganj to identify etiology, pathways of transmission, and factors contributing to these outbreaks.

METHODS

We defined case-patients with severe diarrhoea as residents from affected communities admitted with ≥3 loose stools per day. We listed case-patients, interviewed and examined them, and collected rectal swabs. We visited the affected communities to explore the water and sanitation infrastructure. We tested the microbial load of water samples from selected case household taps, tube wells, and pump stations. We conducted anthropological investigations to understand community perceptions regarding the outbreaks.

RESULTS

We identified 21 case-patients from Bogra and 84 from Kishorganj. The median age in Bogra was 23 years, and 21 years in Kishorganj. There were no reported deaths. We isolated Vibrio in 29% (5/17) of rectal swabs from Bogra and in 40% (8/20) from Kishorganj. We found Vibrio in 1/8 tap water samples from Bogra and in both of the samples from Kishorganj. We did not find Vibrio in water samples from pumps or tube wells in either outbreak. Ground water extracted through deep tube wells was supplied intermittently through interconnected pipes without treatment in both areas. We found leakages in the water pipes in Bogra, and in Kishorganj water pipes passed through open sewers.

CONCLUSION

The rapid onset of severe diarrhoea predominantly affecting adults and the isolation of cholera in rectal swabs confirmed that these outbreaks were caused by Vibrio cholerae. The detection of Vibrio in water samples organisms from taps but not from pumps or tube wells, suggested contamination within the pipes. Safe water provision is difficult in municipalities where supply is intermittent, and where pipes commonly leak. Research to develop and evaluate water purification strategies could identify appropriate approaches for ensuring safe drinking water in resource-poor cities.

Severity of diarrhea and malnutrition among under five-year-old children in rural Bangladesh

Enteric pathogens are commonly associated with diarrhea among malnourished children. This study aimed to determine the association between the severity of diarrheal illnesses and malnutrition among under 5-year-old children. During 2010 and 2011, we studied 2,324 under 5-year-old diarrheal children with mild disease (MD) and moderate-to-severe disease (MSD) attending a hospital in Bangladesh. Children with MSD were more likely to be malnourished compared with children with MD (35% versus 24%, P < 0.001). In multivariate analysis, malnutrition (odds ratio [95% confidence interval] = 1.53 [1.22, 1.92]), age of the child (24-59 months; 1.67 [1.28, 2.19]), fever (1.65 [1.28, 2.12]), abdominal pain (1.87 [1.48, 2.37]), straining (5.93 [4.80, 7.33]), and infection with Shigella (3.26 [2.38, 4.46]) and Vibrio cholerae (2.21 [1.07, 4.58]) were shown to be significantly associated with MSD. Factors significantly associated with malnutrition were disease severity (1.56 [1.24, 1.95]), age (24-59 months; 1.75 [1.38, 2.22]), mother's schooling (1.54 [1.16, 2.04]), and monthly household income (1.71 [1.42, 2.07]). Childhood malnutrition was associated with dysentery and dehydrating diarrhea.

Frequency of reexposure to Vibrio cholerae O1 evaluated by subsequent vibriocidal titer rise after an episode of severe cholera in a highly endemic area in Bangladesh

Vibriocidal antibody is a marker of recent exposure to Vibrio cholerae O1 infection. We examined vibriocidal titers for 1 year after an episode of severe cholera in patients in Dhaka, Bangladesh; 16 of 53 (30%) patients had a fourfold or greater increase in vibriocidal titer between 6 and 12 months after an episode of severe cholera, suggesting reexposure to the organism. Among patients with rises in titers during follow-up, the patients initially infected with serotype Ogawa had earlier rises in titer than the patients initially infected with serotype Inaba. These data and others suggest that an episode of severe cholera protects against symptomatic disease for several years, but reexposure to the organism occurs frequently in an endemic area, with immunological boosts beginning as early as 6 months after severe disease. Repeated exposures to V. cholerae in endemic areas may be a necessary component for long-lasting protection against severe disease.

Antigen-specific memory T cell responses after vaccination with an oral killed cholera vaccine in Bangladeshi children and comparison to responses in patients with naturally acquired cholera

Young children, older children, and adults develop comparable levels and durations of immunity following cholera. In comparison, young children receiving oral killed cholera vaccines (OCV) develop a lower level and shorter duration of protection than those of older children and adults. The reasons for this are unclear. We investigated OCV-induced memory T cell responses in younger and older children and compared responses to those in children with cholera. We found that patients with cholera developed significant levels of toxin-specific effector memory T cells (T(EM)) with follicular helper and gut-homing characteristics. Older children (6 to 14 years of age) receiving two doses of OCV containing recombinant cholera toxin B subunit (rCTB) had more modest T(EM) responses with follicular helper and gut-homing characteristics, but younger vaccinees (24 to 71 months of age) did not develop T(EM) responses. The T(EM) response correlated positively with subsequent IgG memory B cell responses specific to rCTB in older vaccinees. Cytokine analyses indicated that cholera patients developed significant Th1, Th17, and Th2 responses, while older children receiving vaccine developed more modest increases in Th1 and Th17 cells. Younger vaccinees had no increase in Th1 cells, a decrease in Th17 cells, and an increase in regulatory T (Treg) cells. Our findings suggest that T cell memory responses are markedly diminished in children receiving OCV, especially young children, compared to responses following naturally acquired cholera, and that these differences affect subsequent development of memory B cell responses. These findings may explain the lower efficacy and shorter duration of protection afforded by OCV in young children.

Individuals with Le(a+b-) blood group have increased susceptibility to symptomatic vibrio cholerae O1 infection

BACKGROUND

Human genetic factors such as blood group antigens may affect the severity of infectious diseases. Presence of specific ABO and Lewis blood group antigens has been shown previously to be associated with the risk of different enteric infections. The aim of this study was to determine the relationship of the Lewis blood group antigens with susceptibility to cholera, as well as severity of disease and immune responses to infection.

METHODOLOGY

We determined Lewis and ABO blood groups of a cohort of patients infected by Vibrio cholerae O1, their household contacts, and healthy controls, and analyzed the risk of symptomatic infection, severity of disease if infected and immune response following infection.

PRINCIPAL FINDINGS

We found that more individuals with cholera expressed the Le(a+b-) phenotype than the asymptomatic household contacts (OR 1.91, 95% CI 1.03-3.56) or healthy controls (OR 1.90, 95% CI 1.13-3.21), as has been seen previously for the risk of symptomatic ETEC infection. Le(a-b+) individuals were less susceptible to cholera and if infected, required less intravenous fluid replacement in hospital, suggesting that this blood group may be associated with protection against V. cholerae O1. Individuals with Le(a-b-) blood group phenotype who had symptomatic cholera had a longer duration of diarrhea and required higher volumes of intravenous fluid replacement. In addition, individuals with Le(a-b-) phenotype also had lessened plasma IgA responses to V. cholerae O1 lipopolysaccharide on day 7 after infection compared to individuals in the other two Lewis blood group phenotypes.

CONCLUSION

Individuals with Lewis blood type Le(a+b-) are more susceptible and Le(a-b+) are less susceptible to V. cholerae O1 associated symptomatic disease. Presence of this histo-blood group antigen may be included in evaluating the risk for cholera in a population, as well as in vaccine efficacy studies, as is currently being done for the ABO blood group antigens.

Concomitant enterotoxigenic Escherichia coli infection induces increased immune responses to Vibrio cholerae O1 antigens in patients with cholera in Bangladesh

Vibrio cholerae O1 and enterotoxigenic Escherichia coli (ETEC) are major bacterial pathogens that cause dehydrating disease requiring hospitalization of children and adults. The cholera toxin (CT) produced by V. cholerae O1 and the heat-labile toxin (LT) and/or heat-stable toxin (ST) of ETEC are responsible for secretory diarrhea. We have observed that about 13% of hospitalized diarrheal patients are concomitantly infected with V. cholerae O1 and ETEC. In order to understand the outcome of such dual infections on the clinical and immunological responses in cholera patients, we studied patients infected with V. cholerae O1 (group VC; n = 25), those infected with both V. cholerae O1 and ETEC (group VCET; n = 25), and those infected with ETEC only (group ET; n = 25). The VCET group showed more severe dehydration and had a higher intake of intravenous fluid and more vomiting than the ETEC group (P = 0.01 to 0.003). The VCET patients showed higher vibriocidal responses and increased antibody titers to cholera toxin and lipopolysaccharide (LPS) in plasma than did the V. cholerae O1 patients (P = 0.02 to <0.001). All responses in the V. cholerae O1 and in the VCET groups were more robust than those seen in the group infected with ETEC only (P = 0.01 to <0.001). We thus show that concomitant colonization with ETEC induces immune responses to V. cholerae antigens that are more robust than those seen with V. cholerae O1 infection alone. It is possible that LT or other factors expressed by ETEC may play a role as a mucosal adjuvant in enhancing the immune responses to V. cholerae O1.

Clinical outcomes in household contacts of patients with cholera in Bangladesh

BACKGROUND

Multiple Vibrio cholerae infections in the same household are common. The objective of this study was to examine the incidence of V. cholerae infection and associated clinical symptoms in household contacts of patients with cholera and to identify risk factors for development of severe dehydration in this cohort.

METHODS

Household contacts of hospitalized patients with cholera were observed with frequent clinical assessments and collection of serum and rectal swab samples for culture for a period of 21 days after presentation of the index case.

RESULTS

One-half (460 of 944) of all contacts reported diarrhea during the study period, and symptoms most frequently began 2 days after presentation of the index case. Antibiotics were used by 199 (43%) of 460 contacts with diarrhea. Results of rectal swab cultures for V. cholerae were positive for 202 (21%) of 944 contacts, and 148 (73%) infected contacts experienced diarrhea. Significant dehydration developed in 26 contacts; predictors of dehydration included vomiting, each additional day of diarrhea, and blood group O status.

CONCLUSIONS

In urban Bangladesh, the burden of diarrheal illness among household contacts of patients with cholera is higher than was previously estimated, and prophylactic intervention is feasible, because the majority of symptomatic cases of V. cholerae infection in contacts begin soon after presentation of the index case. Re-evaluation of targeted chemoprophylaxis for household contacts of patients with cholera may be warranted.

Development of immunoglobulin M memory to both a T-cell-independent and a T-cell-dependent antigen following infection with Vibrio cholerae O1 in Bangladesh

Vibrio cholerae O1 can cause severe watery diarrhea that can be life-threatening without treatment. Infection results in long-lasting protection against subsequent disease. Development of memory B cells of the immunoglobulin G (IgG) and IgA isotypes to V. cholerae O1 antigens, including serotype-specific lipopolysaccharide (LPS) and the B subunit of cholera toxin (CTB), after cholera infection has been demonstrated. Memory B cells of the IgM isotype may play a role in long-term protection, particularly against T-cell-independent antigens, but IgM memory has not been studied in V. cholerae O1 infection. Therefore, we assayed acute- and convalescent-phase blood samples from cholera patients for the presence of memory B cells that produce cholera antigen-specific IgM antibody upon polyclonal stimulation in in vitro culture. We also examined the development of serological and antibody-secreting cell responses following infection. Subjects developed significant IgM memory responses by day 30 after infection, both to the T-cell-independent antigen LPS and to the T-cell-dependent antigen CTB. No significant corresponding elevations in plasma IgM antibodies or circulating IgM antibody-secreting cells to CTB were detected. In 17 subjects followed to day 90 after infection, significant persistence of elevated IgM memory responses was not observed. The IgM memory response to CTB was negatively correlated with the IgG plasma antibody response to CTB, and there was a trend toward negative correlation between the IgM memory and IgA plasma antibody responses to LPS. We did not observe an association between the IgM memory response to LPS and the vibriocidal titer.

Memory T-cell responses to Vibrio cholerae O1 infection

Vibrio cholerae O1 can cause diarrheal disease that may be life-threatening without treatment. Natural infection results in long-lasting protective immunity, but the role of T cells in this immune response has not been well characterized. In contrast, robust B-cell responses to V. cholerae infection have been observed. In particular, memory B-cell responses to T-cell-dependent antigens persist for at least 1 year, whereas responses to lipopolysaccharide, a T-cell-independent antigen, wane more rapidly after infection. We hypothesize that protective immunity is mediated by anamnestic responses of memory B cells in the gut-associated lymphoid tissue, and T-cell responses may be required to generate and maintain durable memory B-cell responses. In this study, we examined B- and T-cell responses in patients with severe V. cholerae infection. Using the flow cytometric assay of the specific cell-mediated immune response in activated whole blood, we measured antigen-specific T-cell responses using V. cholerae antigens, including the toxin-coregulated pilus (TcpA), a V. cholerae membrane preparation, and the V. cholerae cytolysin/hemolysin (VCC) protein. Our results show that memory T-cell responses develop by day 7 after infection, a time prior to and concurrent with the development of B-cell responses. This suggests that T-cell responses to V. cholerae antigens may be important for the generation and stability of memory B-cell responses. The T-cell proliferative response to VCC was of a higher magnitude than responses observed to other V. cholerae antigens.

Immunologic responses to Vibrio cholerae in patients co-infected with intestinal parasites in Bangladesh

Background

Infection with intestinal helminths is common and may contribute to the decreased efficacy of Vibrio cholerae vaccines in endemic compared to non-endemic areas. However, the immunomodulatory effects of concomitant intestinal parasitic infection in cholera patients have not been systematically evaluated.

Methods

We evaluated V. cholerae-specific immune responses in a cohort of patients with severe cholera. 361 patients completed 21 days of observation and 53 (15%) had evidence of a concomitant intestinal parasitic infection based on direct microscopy. Although there were no significant differences in the vibriocidal or lipopolysaccharide (LPS)-specific immune responses to V. cholerae, helminth-infected cholera patients had decreased fecal and serum IgA immune responses to the B subunit of cholera toxin (CTB) as well as a more modest decrease in serum IgG response to CTB. These findings remained significant for all classes of helminth infection and when controlling for potential confounding variables such as age and nutritional status. Although we hypothesized the differential effect on CTB and LPS immune responses was due to T-cell-dependent immunomodulatory effects of helminth infection, we did not find additional evidence to support a classic Th1 or Th2 polarization of the immune response to V. cholerae infection related to parasite infection.

Conclusions/Significance

The finding that helminth infection has a profound association with the mucosal humoral immune response to V. cholerae has implications for the development of protective immunity in cholera-endemic areas and provides an additional basis for deworming programs in cholera-endemic areas. Additional studies, including further characterization of the role of T cells in the immune response to human V. cholerae infection and the development of an animal model of co-infection, may provide additional insight into the mechanisms underlying these findings.

Vibrio cholerae causes cholera, a severe diarrhea that may lead to fatal dehydration if not treated. Cholera occurs mostly in impoverished areas where there is poor sanitation and intestinal parasites are also common. However, little is known about the relationship between intestinal parasites and cholera. To learn about how parasites affect the immune response to Vibrio cholerae, this article describes 361 patients with cholera, including 53 who had intestinal parasitic infection. We found that cholera patients with parasitic worms had decreased antibody response to cholera toxin. The decrease was greatest in IgA antibodies, which are secreted in the intestine. However, patients with worm infection did not have a difference in their immune response to lipopolysaccharide, a sugar-based molecule that is important for immunity. These different effects on the immune response to cholera toxin and lipopolysaccharide could be explained by the effect of parasitic infection on CD4+ T cells, a type of cell that influences the development of the antibody response to proteins such as cholera toxin but may not always influence the response to sugar-based molecules. The finding that worm infection is associated with decreased immune responses to cholera provides an additional reason for deworming in cholera-endemic areas.

A comparison of clinical and immunologic features in children and older patients hospitalized with severe cholera in Bangladesh

BACKGROUND

: Infection with Vibrio cholerae induces protection from subsequent severe disease, suggesting that an effective vaccine could be an important preventive strategy. Available vaccines provide less protection against cholera than natural infection, particularly in children.

METHODS

: We examined a cohort of 121 children (2 years-12 years of age) and 276 older patients (>12 years of age) hospitalized with cholera in Dhaka, Bangladesh over a 4-year period, to compare clinical features in older patients and children and immune responses to key antigens.

RESULTS

: Older patients had more severe disease. Children with cholera were more commonly retinol deficient, while zinc deficiency was equally prevalent in both groups. Children developed higher vibriocidal and serum immune responses to the B subunit of cholera toxin (CTB). In contrast, older patients mounted higher immune responses to 2 other key V. cholerae antigens, the lipopolysaccharide (LPS) and toxin coregulated pilus antigens (TcpA). We compared immune responses following infection with those occurring after receipt of a live, oral vaccine in both children and older patients in Bangladesh, during a similar time period. The response rates for vibriocidal and LPS antibodies were higher after infection than after vaccination. Both vaccinated older patients and children responded poorly to CTB and TcpA.

CONCLUSIONS

: Although children developed vigorous vibriocidal and CTB-specific responses following infection, they had lessened responses to LPS and TcpA compared with older patients, as well as lessened responses to vaccination. More studies need to be carried out to determine factors, including micronutrient interventions that can improve responses in children to both natural infection and vaccination.

Susceptibility to Vibrio cholerae infection in a cohort of household contacts of patients with cholera in Bangladesh

Background

Despite recent progress in understanding the molecular basis of Vibrio cholerae pathogenesis, there is relatively little knowledge of the factors that determine the variability in human susceptibility to V. cholerae infection.

Methods and Findings

We performed an observational study of a cohort of household contacts of cholera patients in Bangladesh, and compared the baseline characteristics of household members who went on to develop culture-positive V. cholerae infection with individuals who did not develop infection. Although the vibriocidal antibody is the only previously described immunologic marker associated with protection from V. cholerae infection, we found that levels of serum IgA specific to three V. cholerae antigens—the B subunit of cholera toxin, lipopolysaccharide, and TcpA, the major component of the toxin–co-regulated pilus—also predicted protection in household contacts of patients infected with V. cholerae O1, the current predominant cause of cholera. Circulating IgA antibodies to TcpA were also associated with protection from V. cholerae O139 infection. In contrast, there was no association between serum IgG antibodies specific to these three antigens and protection from infection with either serogroup. We also found evidence that host genetic characteristics and serum retinol levels modify susceptibility to V. cholerae infection.

Conclusions

Our observation that levels of serum IgA (but not serum IgG) directed at certain V. cholerae antigens are associated with protection from infection underscores the need to better understand anti–V. cholerae immunity at the mucosal surface. Furthermore, our data suggest that susceptibility to V. cholerae infection is determined by a combination of immunologic, nutritional, and genetic characteristics; additional factors that influence susceptibility to cholera remain unidentified.

Vibrio cholerae is the bacterium that causes cholera, a severe form of diarrhea that leads to rapid and potentially fatal dehydration when the infection is not treated promptly. Cholera remains an important cause of diarrhea globally, and V. cholerae continues to cause major epidemics in the most vulnerable populations. Although there have been recent discoveries about how the bacterium adapts to the human intestine and causes diarrhea, there is little understanding of why some people are protected from infection with V. cholerae. This article describes several factors that are associated with the risk of developing V. cholerae infection among people living in the same household with a patient with severe cholera who are at high risk of contracting the infection. One of the findings is that IgA antibodies, a type of antibody associated with immunity at mucosal surfaces such as the intestine, that target several components of the bacteria are associated with immunity to V. cholerae infection. This article also describes genetic and nutritional factors that additionally influence susceptibility to V. cholerae infection.

Complexity of rice-water stool from patients with Vibrio cholerae plays a role in the transmission of infectious diarrhea

At the International Centre for Diarrhoeal Disease Research, Bangladesh, one-half of the rice-water stool samples that were culture-positive for Vibrio cholerae did not contain motile V. cholerae by standard darkfield microscopy and were defined as darkfield-negative (DF(-)). We evaluated the host and microbial factors associated with DF status, as well as the impact of DF status on transmission. Viable counts of V. cholerae in DF(-) stools were three logs lower than in DF(+) stools, although DF(-) and DF(+) stools had similar direct counts of V. cholerae by microscopy. In DF(-) samples, non-V. cholerae bacteria outnumbered V. cholerae 10:1. Lytic V. cholerae bacteriophage were present in 90% of DF(-) samples compared with 35% of DF(+) samples, suggesting that bacteriophage may limit culture-positive patients from producing DF(+) stools. V. cholerae in DF(-) and DF(+) samples were found both planktonically and in distinct nonplanktonic populations; the distribution of organisms between these compartments did not differ appreciably between DF(-) and DF(+) stools. This biology may impact transmission because epidemiological data suggested that household contacts of a DF(+) index case were at greater risk of infection with V. cholerae. We propose a model in which V. cholerae multiply in the small intestine to produce a fluid niche that is dominated by V. cholerae. If lytic phage are present, viable counts of V. cholerae drop, stools become DF(-), other microorganisms bloom, and cholera transmission is reduced.

Mucosal and systemic immune responses in patients with diarrhea due to CS6-expressing enterotoxigenic Escherichia coli

Colonization factor CS6 expressed by enterotoxigenic Escherichia coli (ETEC) is a nonfimbrial polymeric protein. A substantial proportion of ETEC strains isolated from patients in endemic settings and in people who travel to regions where ETEC is endemic are ETEC strains expressing CS6, either alone or in combination with fimbrial colonization factor CS5 or CS4. However, relatively little is known about the natural immune responses elicited against CS6 expressed by ETEC strains causing disease. We studied patients who were hospitalized with diarrhea (n = 46) caused by CS6-expressing ETEC (ETEC expressing CS6 or CS5 plus CS6) and had a disease spectrum ranging from severe dehydration (27%) to moderate or mild dehydration (73%). Using recombinant CS6 antigen, we found that more than 90% of the patients had mucosal immune responses to CS6 expressed as immunoglobulin (IgA) antibody-secreting cells (ASC) or antibody in lymphocyte supernatant (ALS) and that about 57% responded with CS6-specific IgA antibodies in feces. More than 80% of the patients showed IgA seroconversion to CS6. Significant increases in the levels of anti-CS6 antibodies of the IgG isotype were also observed in assays for ASC (75%), ALS (100%), and serum (70%). These studies demonstrated that patients hospitalized with the noninvasive enteric pathogen CS6-expressing ETEC responded with both mucosal and systemic antibodies against CS6. Studies are needed to determine if the anti-CS6 responses protect against reinfection and if protective levels of CS6 immunity are induced by vaccination.

Blood group, immunity, and risk of infection with Vibrio cholerae in an area of endemicity

Individuals with blood group O are more susceptible than other individuals to severe cholera, although the mechanism underlying this association is unknown. To assess the respective roles of both intrinsic host factors and adaptive immune responses that might influence susceptibility to infection with Vibrio cholerae, we prospectively followed a cohort of household contacts of patients with cholera in Bangladesh. In this study, we made the novel observation that persons with blood group O were less likely than those with other blood groups to become infected with V. cholerae O1 (odds ratio [OR], 0.67; 95% confidence interval [CI], 0.53 to 0.85; P = 0.008). Consistent with prior studies, however, household contacts with blood group O were more likely to develop severe illness if infected with V. cholerae O1 (OR, 2.3; 95% CI, 0.98 to 5.59; P = 0.05). While blood group O protected significantly against infection with V. cholerae O1, there was no evidence of protection against V. cholerae O139. A multivariate analysis demonstrated that the association between blood group O and protection from infection with V. cholerae O1 was independent of age, gender, and baseline anti-cholera toxin and vibriocidal antibody titers. Based on this epidemiologic evidence, we propose a hypothesis for understanding the association between blood group O and the risk of infection with V. cholerae O1 and O139 as well as the risk of developing severe symptoms once infected.

Antigen-specific immunoglobulin A antibodies secreted from circulating B cells are an effective marker for recent local immune responses in patients with cholera: comparison to antibody-secreting cell responses and other immunological markers

Gut-derived lymphocytes transiently migrate through the peripheral circulation before homing back to mucosal sites and can be detected using an ELISPOT-based antibody secreting cell (ASC) assay. Alternatively, transiently circulating lymphocytes may be cultured in vitro, and culture supernatants may be assayed for antigen-specific responses (antibody in lymphocyte supernatant [ALS] assay). The ALS assay has not been validated extensively in natural mucosal infection, nor has the ALS response been compared to the ASC assay and other cholera-specific immunological responses. Accordingly, we examined immune responses in 30 adult patients with acute cholera in Bangladesh, compared with 10 healthy controls, measuring ALS-immunoglobulin A (IgA), ASC-IgA, and serum and fecal IgA responses to two potent Vibrio cholerae immunogens, the nontoxic B subunit of cholera toxin (CtxB) and lipopolysaccharide (LPS) and a weaker V. cholerae immunogen, the mannose-sensitive hemagglutinin (MSHA). We found significant increases of anti-CtxB, anti-LPS, and anti-MSHA IgA in supernatants of lymphocytes cultured 7 days after onset of cholera using the ALS assay. We found that ALS and ASC responses correlated extremely well; both had comparable sensitivities as the vibriocidal responses, and both procedures were more sensitive than fecal IgA measurements. An advantage of the ALS assay for studying mucosal immune responses is the ability to freeze antibodies in supernatants for subsequent evaluation; like the ASC assay, the ALS assay can distinguish recent from remote mucosal infection, a distinction that may be difficult to make in endemic settings using other procedures.

Isolation and characterization of bacteriophage-resistant mutants of Vibrio cholerae O139

Vibrio cholerae O139 strains produce a capsule which is associated with complement resistance and is used as a receptor by bacteriophage JA1. Spontaneous JA1-resistant mutants were found to have several phenotypes, with loss of capsule and/or O-antigen from the cell surface. Determination of the residual complement resistance and infant mouse colonization potential of each mutant suggested that production of O-antigen is of much greater significance than the presence of capsular material for both of these properties. Two different in vitro assays of complement resistance were compared and the results of one shown to closely reflect the comparative recoveries of bacteria from the colonization experiments. Preliminary complementation studies implicated two rfb region genes, wzz and wbfP, as being essential for the biosynthesis of capsule but not O-antigen.

Susceptibility of Vibrio cholerae O139 to antibody-dependent, complement-mediated bacteriolysis

Volunteer studies with Vibrio cholerae O1 have shown that the best correlate of a vaccine's protective efficacy is its propensity to elicit serum bactericidal responses in its recipients. Attempts to detect such responses following infection with V. cholerae O139, however, have met with varying success. Using a tube-based assay which involves viable counting, we now report that strains of serogroup O139 can appear to be sensitive or resistant to a fixed concentration of complement in the presence of antibody, depending on assay conditions. Susceptibility to lysis is critically dependent on the availability of complement, but with O139 indicator strains this is not simply determined by the concentration of serum added to the reaction mix. The nature of the assay diluent and the concentration of indicator bacteria can also dramatically affect bactericidal end points, whereas such variables have minimal significance with O1 indicator bacteria. Although some laboratories use unencapsulated mutant strains to seek evidence of seroconversion following exposure to V. cholerae O139, this is not necessary, and our findings question the significance of capsule expression as a determinant of complement sensitivity when antibody is present. The medium used for growth of the indicator strain and the particular strain used appeared to be unimportant. Each of seven O139 isolates tested was found to be lysed by antibody and complement in our standard assay system, which allowed the detection of significant serum bactericidal responses in 9 of 11 cases of O139 disease.

Comparison of immune responses in patients infected with Vibrio cholerae O139 and O1

Vibrio cholerae O139 has recently emerged as the second etiologic agent of cholera in Asia. A study was carried out to evaluate the induction of specific immune responses to the organism in V. cholerae O139-infected patients. The immune responses to V. cholerae O139 Bengal were studied in patients by measuring antibody-secreting cells (ASC), as well as vibriocidal and antitoxic antibodies in the circulation. These responses were compared with those in patients with V. cholerae O1 disease. Strong immunoglobulin A (IgA) and IgM ASC responses were seen against the homologous lipopolysaccharide or serogroup of V. cholerae. The magnitude and isotype of the responses were similar in O139- and O1-infected patients. Vibriocidal antibody responses were seen against bacteria of the homologous but not heterologous serogroup, and these responses reflect the lack of cross-protection between the infections caused by the two serogroups. The two groups of patients showed comparable cholera toxin-specific ASC responses, with the IgG isotype dominating over the IgA isotype, as well as comparable antitoxic immune responses in plasma. These results suggest that despite having a polysaccharide capsule, V. cholerae O139 induces systemic and intestine-derived ASC responses in peripheral blood comparable to those seen in patients with V. cholerae O1 disease.

Immune response to the mannose-sensitive hemagglutinin in patients with cholera due to Vibrio cholerae O1 and O0139

The mannose-sensitive hemagglutinin (MSHA) is a type 4 pilus present in Vibrio cholerae O1 strains of the El Tor biotype, as well as in strains of serogroup O139. It has been shown to be a colonization antigen in animal models. The aim of this study was to investigate systemic and local antibody responses to MSHA in adult patients with cholera due to V. cholerae O1 and O139. Twenty-four of 28 (86%) patients with O1 cholera and 11 of 17 (65%) patients with O139 cholera showed significant increases in MSHA-specific immunoglobulin A (IgA) and IgM antibody-secreting cells (ASCs) 7 days after the onset of disease. However, the magnitude of the ASC response in O1 cholera patients was significantly higher than that in the O139 cholera patients in both IgA-producing (P = 0.015) and IgM-producing (P = 0.029) cells. Both groups of patients responded with antibody responses to MSHA in plasma, seroconverting with both IgA (63 to 70% of patients) and IgG (43 to 59% of patients) antibodies. Compared to the MSHA-specific antibody levels determined in healthy controls (n = 10), more than 90% of O1 and O139 cholera patients showed responses to MSHA of both the IgA and the IgG isotypes. About 70% of the patients in both groups also had antibody responses to MSHA in their feces. In summary, we demonstrated that MSHA is immunogenic, giving rise to both systemic and local antibodies in patients with cholera due to both O1 and O139 serogroups.

Cloning and sequence of a region of Vibrio cholerae O139 Bengal and its use in PCR-based detection

We isolated and characterized a Vibrio cholerae O139 Bengal-specific DNA region by arbitrary PCR. The fragment contains open reading frames encoding two potential glycosyltransferases possibly involved in capsular polysaccharide or lipopolysaccharide biosynthesis. In order to evaluate the possibility that this region could be used for the specific detection of V. cholerae O139 Bengal, a PCR system was established. The specificity and sensitivity of the PCR were investigated by analyzing 240 strains within the family Vibrionaceae and 178 stains of other gram-negative bacteria. All V. cholerae O139 Bengal strains tested were positive, and none of the 384 control strains were amplified. The sensitivity of the assay was 10(2) CFU/ml.

Monoclonal antibodies to the enterotoxin of Bacteroides fragilis: production, characterization, and immunodiagnostic application

A monoclonal antibody, ICT11, specific for the toxin of enterotoxigenic Bacteroides fragilis (ETBF) neutralized the cytotoxic effect of the toxin on human colonic cell line HT-29/C1. In an evaluation using 115 diarrheal stool specimens and culture as the "gold standard," the assay showed a sensitivity of 85% and a specificity of 100%. An ICT11-based sandwich enzyme-linked immunosorbent assay showed a sensitivity of 100% and a specificity of 98% for direct detection of toxin from stool samples compared with those of culture. Thus, ICT11-based assays will be useful for screening for ETBF.

Analysis of Vibrio cholerae O139 Bengal isolated from different geographical areas using macrorestriction DNA analysis

Vibrio cholerae O139 isolated from different countries, as well as from different locations within a country, were examined using macrorestriction DNA analysis to determine the clonality of the O139 strains. NotI digests of genomic DNA of representative strains from Nepal, India, Bangladesh, China, Thailand, and Malaysia revealed very similar but not identical patterns. Examinations of the banding patterns generated by pulsed-field gel electrophoresis of strains isolated within countries revealed complete homogeneity. These results further reiterate the spread of an identical clone of V. cholerae O139 although it appears that genetic polymorphism among the O139 strains is becoming apparent.

Monoclonal antibodies specific for the bundle-forming pilus of enteropathogenic Escherichia coli

The bundle-forming pilus (BFP) produced by enteropathogenic Escherichia coli (EPEC) is associated with the presence of a large EPEC adherence factor plasmid and the formation of localized adherence clusters on tissue culture cells. Three mouse monoclonal antibodies (ICA2, ICA3, and ICA4) were produced against BFP purified from EPEC B171 (O111:NM). These monoclonal antibodies reacted in immunoblots with different epitopes of the 19.5-kDa bundlin subunit of BFP of heterologous EPEC. These reagents could serve as diagnostic tools for the identification of EPEC as well as for studying the role of BfpA in the interaction of EPEC with eukaryotic cells.

Characterization of Aeromonas trota strains that cross-react with Vibrio cholerae O139 Bengal

It has previously been shown that Vibrio cholerae O139 Bengal shares antigens with V. cholerae serogroups O22 and O155. We detected six surface water isolates of Aeromonas trota that agglutinated in polyclonal antisera to V. cholerae O139 and V. cholerae O22 but not in antiserum to V. cholerae O155. On the basis of agglutinin-absorption studies, the antigenic relationship between the cross-reacting bacteria were found to be in an a,b-a,c fashion, where a is the common antigenic epitope and b and c are unique epitopes. The antigen sharing between A. trota strains and V. cholerae O139 was confirmed in immunoblot studies. However, A. trota strains did not react with two monoclonal antibodies specific for V. cholerae O139 and, consequently, tested negative in the Bengal SMART rapid diagnostic test for V. cholerae O139 which uses one of the monoclonal antibodies. A polyclonal antiserum to a cross-reacting A. trota strain cross-protected infant mice against cholera on challenge with virulent V. cholerae O139. All A. trota strains were cytotoxic for HeLa cells, positive for adherence to HEp-2 cells, and weakly invasive for HEp-2 cells; one strain was heat-stable toxin positive in the suckling mouse assay; however, all strains were negative for cholera toxin-like enterotoxin. Studies on bacteria that share somatic antigen with V. cholerae O139 may shed further light on the genesis of V. cholerae O139.

Comparison of the vibriocidal antibody response in cholera due to Vibrio cholerae O139 Bengal with the response in cholera due to Vibrio cholerae O1

Vibrio cholerae serogroup O139, now considered to be the second organism capable of causing epidemic severe dehydrating cholera, contains a capsular polysaccharide which makes it difficult for it to be used in the conventional vibriocidal antibody assay optimized for V. cholerae O1. After modification of the procedure, which involved the use of specific bacterial strains, a lower bacterial inoculum, and increased amounts of complement, the vibriocidal antibody responses to V. cholerae O139 were measured in acute- and convalescent-phase sera from 33 V. cholerae O139-infected and 18 V. cholerae O1-infected patients and in single serum samples from 20 healthy control subjects. The responses in these individuals to V. cholerae O1 strains were also determined. Significant elevations in the homologous antibody response were found only in the convalescent-phase sera from both groups of patients with cholera. These findings may explain the basis for the lack of heterologous protection between the two serogroups of V. cholerae. Healthy controls had higher background levels of vibriocidal antibody to V. cholerae O1 than to V. cholerae O139.

Isolation of sucrose late-fermenting and nonfermenting variants of Vibrio cholerae O139 Bengal: implications for diagnosis of cholera

The sucrose-containing selective medium thiosulfate-citrate-bile salt-sucrose agar missed a sucrose nonfermenting and four sucrose late-fermenting variant strains of Vibrio cholerae O139 Bengal from diarrheal stools. These strains were, however, correctly identified as V. cholerae O139 on a sucrose-deficient selective medium, taurocholate-tellurite-gelatin agar.

Evaluation of the monoclonal antibody-based kit Bengal SMART for rapid detection of Vibrio cholerae O139 synonym Bengal in stool samples

A monoclonal antibody-based test, Bengal SMART, was developed for rapid detection of Vibrio cholerae O139 synonym Bengal directly from stool specimens. The test, which takes about 15 min to complete, was used to screen 189 diarrheal stool specimens. The results were compared with those of a monoclonal antibody-based coagglutination test (COAT) and the conventional culture methods used as the "gold standard" for detection of V. cholerae O139. The Bengal SMART test showed a sensitivity of 100% and a specificity of 97% in comparison with the gold standard. It also fared better than COAT, which had a sensitivity of 96% for rapid detection of V. cholerae O139 synonym Bengal. These results show that Bengal SMART is suitable for use in field settings for rapid diagnosis of cholera caused by V. cholerae O139.

Vibrio cholerae O139 Bengal

Images

Development and evaluation of rapid monoclonal antibody-based coagglutination test for direct detection of Vibrio cholerae O139 synonym Bengal in stool samples

A monoclonal antibody-based coagglutination test directly detected Vibrio cholerae O139 synonym Bengal in 83 of 120 watery diarrheal stool specimens; on culture, 90 samples were positive. Thus, with 92% sensitivity, 100% specificity, and 100% positive and 95% negative predictive values, the coagglutination test is a useful rapid test for V. cholerae O139.