Detection of Vibrio cholerae O1 and O139 in environmental waters of rural Bangladesh: a flow-cytometry-based field trial

Comparison of O-specific polysaccharide responses in patients following infection with Vibrio cholerae O139 versus vaccination with a bivalent (O1/O139) oral killed cholera vaccine in Bangladesh

Cholera caused by Vibrio cholerae O139 emerged in the early 1990s and spread rapidly to 11 Asian countries before receding for unclear reasons. Protection against cholera is serogroup-specific, which is defined by the O-specific polysaccharide (OSP) component of lipopolysaccharide (LPS). V. cholerae O139 also expresses the OSP-capsule. We, therefore, assessed antibody responses targeting V. cholerae O139 OSP, LPS, capsule, and vibriocidal responses in patients in Bangladesh with cholera caused by V. cholerae O139. We compared these responses to those of age-gender-blood group-matched recipients of the bivalent oral cholera vaccine (OCV O1/O139). We found prominent OSP, LPS, and vibriocidal responses in patients, with a high correlation between these responses. OSP responses primarily targeted the terminal tetrasaccharide of OSP. Vaccinees developed OSP, LPS, and vibriocidal antibody responses, but of significantly lower magnitude and responder frequency (RF) than matched patients. We separately analyzed responses in pediatric vaccinees born after V. cholerae O139 had receded in Bangladesh. We found that OSP responses were boosted in children who had previously received a single dose of bivalent OCV 3 yr previously but not in vaccinated immunologically naïve children. Our results suggest that OSP-specific responses occur during cholera caused by V. cholerae O139 despite the presence of capsules, that vaccination with bivalent OCV is poorly immunogenic in the short term in immunologically naïve individuals, but that OSP-specific immune responses can be primed by previous exposure, although whether such responses can protect against O139 cholera is uncertain. IMPORTANCE Cholera is a severe dehydrating illness in humans caused by Vibrio cholerae serogroups O1 or O139. Protection against cholera is serogroup-specific, which is defined by the O-specific polysaccharide (OSP) of V. cholerae LPS. Yet, little is known about immunity to O139 OSP. In this study, we assessed immune responses targeting OSP in patients from an endemic region with cholera caused by V. cholerae O139. We compared these responses to those of the age-gender-blood group-matched recipients of the bivalent oral cholera vaccine. Our results suggest that OSP-specific responses occur during cholera caused by V. cholerae O139 and that the OSP responses primarily target the terminal tetrasaccharide of OSP. Our results further suggest that vaccination with the bivalent vaccine is poorly immunogenic in the short term for inducing O139-specific OSP responses in immunologically naïve individuals, but OSP-specific immune responses can be primed by previous exposure or vaccination.

Usability of Rapid Cholera Detection Device (OmniVis) for Water Quality Workers in Bangladesh: Iterative Convergent Mixed Methods Study

BACKGROUND

Cholera poses a significant global health burden. In Bangladesh, cholera is endemic and causes more than 100,000 cases each year. Established environmental reservoirs leave millions at risk of infection through the consumption of contaminated water. The Global Task Force for Cholera Control has called for increased environmental surveillance to detect contaminated water sources prior to human infection in an effort to reduce cases and deaths. The OmniVis rapid cholera detection device uses loop-mediated isothermal amplification and particle diffusometry detection methods integrated into a handheld hardware device that attaches to an iPhone 6 to identify and map contaminated water sources.

OBJECTIVE

The aim of this study was to evaluate the usability of the OmniVis device with targeted end users to advance the iterative prototyping process and ultimately design a device that easily integrates into users' workflow.

METHODS

Water quality workers were trained to use the device and subsequently completed an independent device trial and usability questionnaire. Pretraining and posttraining knowledge assessments were administered to ensure training quality did not confound trial and questionnaire.

RESULTS

Device trials identified common user errors and device malfunctions including incorrect test kit insertion and device powering issues. We did not observe meaningful differences in user errors or device malfunctions accumulated per participant across demographic groups. Over 25 trials, the mean time to complete a test was 47 minutes, a significant reduction compared with laboratory protocols, which take approximately 3 days. Overall, participants found the device easy to use and expressed confidence and comfort in using the device independently.

CONCLUSIONS

These results are used to advance the iterative prototyping process of the OmniVis rapid cholera detection device so it can achieve user uptake, workflow integration, and scale to ultimately impact cholera control and elimination strategies. We hope this methodology will promote robust usability evaluations of rapid pathogen detection technologies in device development.

Diagnostic techniques for rapid detection of Vibrio cholerae O1/O139

Cholera caused by the toxigenic Vibrio cholerae is still a major public health problem in many countries. This disease is mainly due to poor sanitation, hygiene and consumption of unsafe water. Several recent epidemics of cholera showed its increasing intensity, duration and severity of the illness. This indicates an urgent need for effective management and preventive measures in controlling the outbreaks and epidemics. In preventing and spread of epidemic cholera, rapid diagnostic tests (RDTs) are useful in screening suspected stool specimens, water/food samples. Several RDTs developed recently are considered as investigative tools in confirming cholera cases, as the culture techniques are difficult to establish and/or maintain. The usefulness of RDTs will be more at the point-of-care facilities as it helps to make appropriate decisions in the management of outbreaks or epidemiological surveillance by the public health authorities. Apart from RDTs, several other tests are available for the direct detection of either V. cholerae or its cholera toxin. Viable but non-culturable (VBNC) state of V. cholerae poses a great challenge in developing RDTs. The aim of this article is to provide an overview of current knowledge about RDT and other techniques with reference to their status and future potentials in detecting cholera/V. cholerae.

Environmental Surveillance of Vibrio cholerae O1/O139 in the Five African Great Lakes and Other Major Surface Water Sources in Uganda

Cholera is a major public health problem in the African Great Lakes basin. Two hypotheses might explain this observation, namely the lakes are reservoirs of toxigenic Vibrio cholerae O1 and O139 bacteria, or cholera outbreaks are a result of repeated pathogen introduction from the neighboring communities/countries but the lakes facilitate the introductions. A prospective study was conducted in Uganda between February 2015 and January 2016 in which 28 selected surface water sources were tested for the presence of V. cholerae species using cholera rapid test and multiplex polymerase chain reaction. Of 322 water samples tested, 35 (10.8%) were positive for V. cholerae non O1/non O139 and two samples tested positive for non-toxigenic atypical V. cholerae O139. None of the samples tested had toxigenic V. cholerae O1 or O139 that are responsible for cholera epidemics. The Lake Albert region registered the highest number of positive tests for V. cholerae non O1/non O139 at 47% (9/19). The peak period for V. cholerae non O1/non O139 positive tests was in March–July 2015 which coincided with the first rainy season in Uganda. This study showed that the surface water sources, including the African Great Lakes in Uganda, are less likely to be reservoirs for the observed V. cholerae O1 or O139 epidemics, though they are natural habitats for V. cholerae non O1/non O139 and atypical non-toxigenic V. cholerae O139. Further studies by WGS tests of non-toxigenic atypical V. cholerae O139 and physicochemical tests of surface water sources that supports V. cholerae should be done to provide more information. Since V. cholerae non O1/non O139 may cause other human infections, their continued surveillance is needed to understand their potential pathogenicity.