Comparison of clinical features and immunological parameters of patients with dehydrating diarrhoea infected with Inaba or Ogawa serotypes of Vibrio cholerae O1

Phage for treatment of Vibrio cholerae infection

Bacteriophages (or "phages") are ubiquitous and the amplest biological entities on our planet. It is a natural enemy of bacteria. Cholera is one of the most known diseases to cause multiple pandemics around the world, killing millions of people. The pathogen of cholera is Vibrio species. Up until the emergence of multidrug resistance, preventive therapeutics like antibiotics were the most effective means of battling bacteria. Globally, one of the most significant challenges in treating microbial infections is the development of drug-resistant strains. Based on their antibacterial properties and unique characteristics, phages are being comprehensively evaluated taxonomically. Moreover, phage-based vaccination is evolving as one of the most encouraging preventive approaches. Due to this, its related research got remarkable recognition. However, due to the rapid emergence of bacterial resistance to antibiotics, the use of phages (phage therapy) could be a major motive for research because the most promising solution lies in bacteriophages. This chapter briefly highlights the promising use of bacteriophages to combat Vibrio-related infectious diseases.

Molecular Basis of the Toxigenic Vibrio cholerae O1 Serotype Switch from Ogawa to Inaba in Haiti

Toxigenic Vibrio cholerae O1 serotype Ogawa was introduced involuntarily into Haiti in October 2010, and virtually all of the clinical strains isolated during the first 5 years of the epidemic were Ogawa. Inaba strains were identified intermittently prior to 2015, with diverse mutations resulting in a common phenotype. In 2015, the percentage of clinical infections due to the Inaba serotype began to rapidly increase, with Inaba supplanting Ogawa as the dominant serotype during the subsequent 4 years. We investigated the molecular basis of the serotype switch and confirmed that all Inaba strains had the same level of mRNA expression of the wbeT genes, as well as the same translation levels for the truncated WbeT proteins in the V. cholerae Inaba isolates. Neither wbeT gene expression levels, differential mutations, or truncation size of the WbeT proteins appeared to be responsible for the successful Inaba switch in 2015. Our phylodynamic analysis demonstrated that the V. cholerae Inaba strains in Haiti evolved directly from Ogawa strains and that a significant increase of diversifying selection at the population level occurred at the time of the Ogawa-Inaba switch. We conclude that the emergence of the Inaba serotype was driven by diversifying selection, independent of the mutational pattern in the wbeT gene. IMPORTANCE Our phylodynamic analysis demonstrated that Vibrio cholerae Inaba strains in Haiti evolved directly from Ogawa strains. Our results support the hypothesis that after an initial Ogawa-dominated epidemic wave, V. cholerae Inaba was able to become the dominant strain thanks to a selective advantage driven by ongoing diversifying selection, independently from the mutational pattern in the wbeT gene.

Effect of HIV status and retinol on immunogenicity to oral cholera vaccine in adult population living in an endemic area of Lukanga Swamps, Zambia

BACKGROUND

We set out to assess the impact of human immunodeficiency virus (HIV) and micronutrient deficiency as indicated by serum retinol levels on the immune responses to Oral Cholera Vaccine (Shanchol™) in a cohort of participants in Lukanga Swamps, Zambia. Cholera remains endemic in Zambia with vaccines being the only effective preventive measures. However, the effect of these vaccines on populations living with HIV has not been widely documented.

METHODS

HIV testing and confirmation was done using the Alere Determine™ HIV-1/2 and Uni-Gold™ kits while vibriocidal antibody assay was applied for vaccine immunogenicity. Serum retinol analysis was assessed by Shimadzu Prominence HCT-2010 High Performance Liquid Chromatography (HPLC). The primary outcome was log transformed geometric mean titre.

RESULTS

From 47 participants screened for HIV, 51% (24) tested positive. There was a statistically significant reduction in Ogawa geometric mean ratio (GMR) by 67% (GMR = 0.33; 95% CI: -0.15, 0.76; p-value = 0.009) attributable to HIV positivity with a non-significant reduction in Inaba GMR by about 50% due to HIV positivity. When doubling of retinol levels modelled, GMR reduction against Ogawa were non-significant but that against Inaba resulted in a significant reduction in geometric mean titer (GMT) (GMT-0.33, C.I 0.16-0.66, p-value 0.002). At 1000copies/ml viral load cut off and 350 cells/μl CD4 counts, Ogawa GMT was two times higher 11.16 (95%CI: 8.20-15.19) versus 6.06 (95%CI: 4.04-9.10) in low viremia participants, and three times higher in above threshold CD4 count participants; 24.81 (95%CI: 18.94-32.50) versus 7.07 (95%CI: 5.22-9.58).

CONCLUSION

Our results show that while Shanchol™ is immunogenic in both HIV+/- individuals, HIV + participants responded poorly. Viral load and CD4 count affected vaccine immunogenicity. More research is required for detailed understanding of this in order to appropriately inform policy and practice.

Gut Microbiota and Development of Vibrio cholerae-Specific Long-Term Memory B Cells in Adults after Whole-Cell Killed Oral Cholera Vaccine

Cholera is a diarrheal disease caused by Vibrio cholerae that continues to be a major public health concern in populations without access to safe water. IgG- and IgA-secreting memory B cells (MBC) targeting the V. cholerae O-specific polysaccharide (OSP) correlate with protection from infection in persons exposed to V. cholerae and may be a major determinant of long-term protection against cholera. Shanchol, a widely used oral cholera vaccine (OCV), stimulates OSP MBC responses in only some people after vaccination, and the gut microbiota is a possible determinant of variable immune responses observed after OCV. Using 16S rRNA sequencing of feces from the time of vaccination, we compared the gut microbiota among adults with and without MBC responses to OCV. Gut microbial diversity measures were not associated with MBC isotype or OSP-specific responses, but individuals with a higher abundance of Clostridiales and lower abundance of Enterobacterales were more likely to develop an MBC response. We applied protein-normalized fecal supernatants of high and low MBC responders to THP-1-derived human macrophages to investigate the effect of microbial factors at the time of vaccination. Feces from individuals with higher MBC responses induced significantly different IL-1β and IL-6 levels than individuals with lower responses, indicating that the gut microbiota at the time of vaccination may "prime" the mucosal immune response to vaccine antigens. Our results suggest the gut microbiota could impact immune responses to OCVs, and further study of microbial metabolites as potential vaccine adjuvants is warranted.

Dissecting serotype-specific contributions to live oral cholera vaccine efficacy

The O1 serogroup of Vibrio cholerae causes pandemic cholera and is divided into the Ogawa and Inaba serotypes. The O-antigen is V. cholerae's immunodominant antigen, and the two serotypes, which differ by the presence or absence of a terminally methylated O-antigen, likely influence development of immunity to cholera and oral cholera vaccines (OCVs). However, there is no consensus regarding the relative immunological potency of each serotype, in part because previous studies relied on genetically heterogeneous strains. Here, we engineered matched serotype variants of a live OCV candidate, HaitiV, and used a germfree mouse model to evaluate the immunogenicity and protective efficacy of each vaccine serotype. By combining vibriocidal antibody quantification with single- and mixed-strain infection assays, we found that all three HaitiV variants-Inaba^V, Ogawa^V, and Hiko^V (bivalent Inaba/Ogawa)-were immunogenic and protective. None of the vaccine serotypes were superior across both of these vaccine metrics, suggesting that the impact of O1-serotype variation in OCV design, although detectable, is subtle. However, all three live vaccines significantly outperformed formalin-killed Hiko^V, supporting the idea that live OCV usage will bolster current cholera control practices. The potency of OCVs was found to be challenge strain-dependent, emphasizing the importance of appropriate strain selection for cholera challenge studies. Our findings and experimental approaches will be valuable for guiding the development of live OCVs and oral vaccines for additional pathogens.

Update on Environmental and Host Factors Impacting the Risk of Vibrio cholerae Infection

Vibrio cholerae is the causative agent of cholera, a diarrheal disease that kills tens of thousands of people each year. Cholera is transmitted primarily by the ingestion of drinking water contaminated with fecal matter, and a safe water supply remains out of reach in many areas of the world. In this Review, we discuss host and environmental factors that impact the susceptibility to V. cholerae infection and the severity of disease.

Influences of Vibrio cholerae Lipid A Types on LPS Bilayer Properties

Lipopolysaccharides (LPS) present in the outer leaflet of Gram-negative bacterial outer membranes protect the bacteria from external threats and influence antibiotic permeability as well as immune system recognition. The structure of lipid A, the anchor of an LPS molecule to the outer membrane, can make direct influences on membrane properties. Particularly, in Vibrio cholerae, a Gram-negative bacterium responsible for cholera, a severe diarrheal disease, modifications of lipid A structures grant antibiotic resistance and are a primary factor that led to the current cholera pandemic. However, the difference in structural properties incurred by such modifications has not been fully explored. In this work, five symmetric bilayer systems comprised of distinct lipid A structures of Vibrio cholerae LPS with O1 O-antigen were modeled and simulated to explore influences of different lipid A types on membrane properties. All-atom molecular dynamics simulations reveal that membrane properties such as hydrophobic thickness, acyl chain order parameter, and area per lipid are largely impacted by lipid A modifications due to differences in composition and acyl chain distortions. The modified lipid A is also less negatively charged, which possibly reveals a resistance mechanism to cationic antimicrobial peptide evasion. These findings present a possible explanation for Vibrio cholerae's immune system evasion properties and establish the differences between the lipid A types, which should be of use for any future study of the Gram-negative bacteria.

Genomics of the Argentinian cholera epidemic elucidate the contrasting dynamics of epidemic and endemic Vibrio cholerae

In order to control and eradicate epidemic cholera, we need to understand how epidemics begin, how they spread, and how they decline and eventually end. This requires extensive sampling of epidemic disease over time, alongside the background of endemic disease that may exist concurrently with the epidemic. The unique circumstances surrounding the Argentinian cholera epidemic of 1992-1998 presented an opportunity to do this. Here, we use 490 Argentinian V. cholerae genome sequences to characterise the variation within, and between, epidemic and endemic V. cholerae. We show that, during the 1992-1998 cholera epidemic, the invariant epidemic clone co-existed alongside highly diverse members of the Vibrio cholerae species in Argentina, and we contrast the clonality of epidemic V. cholerae with the background diversity of local endemic bacteria. Our findings refine and add nuance to our genomic definitions of epidemic and endemic cholera, and are of direct relevance to controlling current and future cholera epidemics.

Phage Types of Vibrio cholerae 01 Biotype ElTor Strains Isolated from India during 2012-2017

Background

Cholera is a primordial disease caused by Vibrio cholerae which existed from centuries in different parts of the world and still shows its periodic, endemic and epidemic presence. Thousands of cholera cases are reported from different parts of India and the disease remains endemic throughout the year. At present, we do not have enough knowledge about the phenotypic nature of the circulating V. cholerae strains in this part of the world.

Objectives

This study was carried out over a period of 6 years with the aim defer with the changes in the prevalence and distribution of biotypes, serotypes and phage types of V. cholerae clinical isolates from various endemic regions of the country to determine phenotypic characteristics of the circulating strains and also to predict the attributes of cholera strains responsible for causing significant outbreaks in future.

Materials and Methods

A total of 1882 V.cholerae O1 isolates from different cholera endemic areas of India were included in this study. V.cholerae strains which were identified as O1 biotype ElTor further analyzed for serotype and phage types using the standard methodologies. Polyvalent O1 and monospecific Inaba and Ogawa antisera were used for serotyping. A panel of five phages of Basu and Mukherjee phage typing scheme and five phages from the new phage typing scheme were used for phage typing analysis following standard methodology.

Results

Maximum numbers of strains were isolated from cholera-endemic states like Gujarat and Maharashtra. All the isolates were confirmed as V. cholerae O1 biotype ElTor and majority of them were serotype Ogawa (93.2%). New phage typing scheme resulted in almost 100% typeable V. cholerae O1 strains included in this study and phage type 27 was the predominant type. Although 80% of the strains used in this study were sensitive to all the vibrio phages, S5 phage was found most efficient in lysing cholera strains indicating its broader host range.

Conclusion

The current study identified phage type 27 as the most dominant type and serotype Ogawa was found continuous in circulation throughout the year which has caused recent cholera outbreaks in India during the past years. Phage sensitivity data propose an alternative cost-effective approach to prevent cholera outbreak by therapeutic uses of typing phages irrespective of origin or clonality of the strains.

Descriptive epidemiology of cholera outbreak in Nigeria, January-November, 2018: implications for the global roadmap strategy

BACKGROUND

The cholera outbreak in 2018 in Nigeria reaffirms its public health threat to the country. Evidence on the current epidemiology of cholera required for the design and implementation of appropriate interventions towards attaining the global roadmap strategic goals for cholera elimination however seems lacking. Thus, this study aimed at addressing this gap by describing the epidemiology of the 2018 cholera outbreak in Nigeria.

METHODS

This was a retrospective analysis of surveillance data collected between January 1st and November 19th, 2018. A cholera case was defined as an individual aged 2 years or older presenting with acute watery diarrhoea and severe dehydration or dying from acute watery diarrhoea. Descriptive analyses were performed and presented with respect to person, time and place using appropriate statistics.

RESULTS

There were 43,996 cholera cases and 836 cholera deaths across 20 states in Nigeria during the outbreak period, with an attack rate (AR) of 127.43/100,000 population and a case fatality rate (CFR) of 1.90%. Individuals aged 15 years or older (47.76%) were the most affected age group, but the proportion of affected males and females was about the same (49.00 and 51.00% respectively). The outbreak was characterised by four distinct epidemic waves, with higher number of deaths recorded in the third and fourth waves. States from the north-west and north-east regions of the country recorded the highest ARs while those from the north-central recorded the highest CFRs.

CONCLUSION

The severity and wide-geographical distribution of cholera cases and deaths during the 2018 outbreak are indicative of an elevated burden, which was more notable in the northern region of the country. Overall, the findings reaffirm the strategic role of a multi-sectoral approach in the design and implementation of public health interventions aimed at preventing and controlling cholera in Nigeria.

Oral immunization with a probiotic cholera vaccine induces broad protective immunity against Vibrio cholerae colonization and disease in mice

Oral cholera vaccines (OCVs) are being increasingly employed, but current killed formulations generally require multiple doses and lack efficacy in young children. We recently developed a new live-attenuated OCV candidate (HaitiV) derived from a Vibrio cholerae strain isolated during the 2010 Haiti cholera epidemic. HaitiV exhibited an unexpected probiotic-like activity in infant rabbits, preventing intestinal colonization and disease by wild-type V. cholerae before the onset of adaptive immunity. However, it remained unknown whether HaitiV would behave similarly to other OCVs to stimulate adaptive immunity against V. cholerae. Here, we orally immunized adult germ-free female mice to test HaitiV’s immunogenicity. HaitiV safely and stably colonized vaccinated mice and induced known adaptive immune correlates of cholera protection within 14 days of administration. Pups born to immunized mice were protected against lethal challenges of both homologous and heterologous V. cholerae strains. Cross-fostering experiments revealed that protection was not dependent on vaccine colonization in or transmission to the pups. These findings demonstrate the protective immunogenicity of HaitiV and support its development as a new tool for limiting cholera.

Oral cholera vaccines are increasingly used as public health tools for prevention of cholera and curtailing the spread of outbreaks. However, current killed vaccines provide minimal protection in young children, who are especially susceptible to this diarrheal disease, and require ~7–14 days between vaccination and development of protective immunity. We recently created HaitiV, a live-attenuated oral cholera vaccine candidate derived from a clinical isolate from the Haiti cholera outbreak. Unexpectedly, HaitiV protected against cholera-like illness in infant rabbits within 24 hours of administration, before the onset of adaptive immunity. However, HaitiV’s capacity to stimulate adaptive immune responses against the cholera pathogen were not investigated. Here, we report that HaitiV induces immunological correlates of protection against cholera in adult germ-free mice and leads to protection against disease in their offspring. Protection against disease was transferable through the milk of the immunized mice and was not due to transmission or colonization of HaitiV in this model. Coupling the immunogenicity data presented here with our previous observation that HaitiV can protect from cholera prior to the induction of adaptive immunity, we propose that HaitiV may provide both rapid-onset short-term protection from disease while eliciting stable and long-lasting immunity against cholera.

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

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

The increased severity in patients presenting to hospital with diarrhea in Dhaka, Bangladesh since the emergence of the hybrid strain of Vibrio cholerae O1 is not unique to cholera patients

BACKGROUND

A hybrid strain of Vibrio cholerae O1 El Tor that expresses a classical cholera toxin (CT) emerged in 2001. This hybrid variant rapidly replaced the previous El Tor strain around the world. The global emergence of this variant coincided with anecdotal reports that cholera patients were presenting with more severe dehydration and disease in many locations.

METHODS

A comparison was made of the severity of disease before and after the emergence of the hybrid strain in cholera patients attending an icddr,b hospital in Dhaka, Bangladesh.

RESULTS

It was found that cholera patients presented with more severe dehydration and severe disease in the later period. However, this was also true for all non-cholera patients as well. In addition, in sub-analyses of patients who presented with rotavirus and enterotoxigenic Escherichia coli (ETEC), similar results were found. Comparing the two periods for differences in patient characteristics, nutritional status, vaccination status, and income, no plausible cause for patients presenting with more severe disease was identified in the later period.

CONCLUSIONS

As a shift in severity for both cholera and non-cholera was observed, these results indicate that the altered El Tor strain cannot fully explain the difference in cholera severity before and after 2001.

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.

Memory B cell responses to Vibrio cholerae O1 lipopolysaccharide are associated with protection against infection from household contacts of patients with cholera in Bangladesh

Vibrio cholerae O1 causes cholera, a dehydrating diarrheal disease. We have previously shown that V. cholerae-specific memory B cell responses develop after cholera infection, and we hypothesize that these mediate long-term protective immunity against cholera. We prospectively followed household contacts of cholera patients to determine whether the presence of circulating V. cholerae O1 antigen-specific memory B cells on enrollment was associated with protection against V. cholerae infection over a 30-day period. Two hundred thirty-six household contacts of 122 index patients with cholera were enrolled. The presence of lipopolysaccharide (LPS)-specific IgG memory B cells in peripheral blood on study entry was associated with a 68% decrease in the risk of infection in household contacts (P = 0.032). No protection was associated with cholera toxin B subunit (CtxB)-specific memory B cells or IgA memory B cells specific to LPS. These results suggest that LPS-specific IgG memory B cells may be important in protection against infection with V. cholerae O1.