Characterization of Vibrio cholerae O139 of an Aquatic Isolate in Northern Vietnam

Beyond Cholera: Characterization of zot-Encoding Filamentous Phages in the Marine Fish Pathogen Vibrio anguillarum

Zonula occludens toxin (Zot) is a conserved protein in filamentous vibriophages and has been reported as a putative toxin in Vibrio cholerae. Recently, widespread distribution of zot-encoding prophages was found among marine Vibrio species, including environmental isolates. However, little is known about the dynamics of these prophages beyond V. cholerae. In this study, we characterized and quantified the zot-encoding filamentous phage VAIϕ, spontaneously induced from the fish pathogen V. anguillarum. VAIϕ contained 6117 bp encoding 11 ORFs, including ORF8^pVAI, exhibiting 27%–73% amino acid identity to Inovirus Zot-like proteins. A qPCR method revealed an average of four VAIϕ genomes per host genome during host exponential growth phase, and PCR demonstrated dissemination of induced VAIϕ to other V. anguillarum strains through re-integration in non-lysogens. VAIϕ integrated into both chromosomes of V. anguillarum by recombination, causing changes in a putative ORF in the phage genome. Phylogenetic analysis of the V. anguillarumInoviridae elements revealed mosaic genome structures related to mainly V. cholerae. Altogether, this study contributes to the understanding of Inovirus infection dynamics and mobilization of zot-like genes beyond human pathogenic vibrios, and discusses their potential role in the evolution of the fish pathogen V. anguillarum.

Genetic diversity of environmental Vibrio cholerae O1 strains isolated in Northern Vietnam

Cholera epidemics have been recorded periodically in Vietnam during the seventh cholera pandemic. Since cholera is a water-borne disease, systematic monitoring of environmental waters for Vibrio cholerae presence is important for predicting and preventing cholera epidemics. We conducted monitoring, isolation, and genetic characterization of V. cholerae strains in Nam Dinh province of Northern Vietnam from Jul 2013 to Feb 2015. In this study, four V. cholerae O1 strains were detected and isolated from 110 analyzed water samples (3.6%); however, none of them carried the cholera toxin gene, ctxA, in their genomes. Whole genome sequencing and phylogenetic analysis revealed that the four O1 isolates were separated into two independent clusters, and one of them diverged from a common ancestor with pandemic strains. The analysis of pathogenicity islands (CTX prophage, VPI-I, VPI-II, VSP-I, and VSP-II) indicated that one strain (VNND_2014Jun_6SS) harbored an unknown prophage-like sequence with high homology to vibriophage KSF-1 phi and VCY phi, identified from Bangladesh and the USA, respectively, while the other three strains carried tcpA gene with a distinct sequence demonstrating a separate clonal lineage. These results suggest that the aquatic environment can harbor highly divergent V. cholera strains and serve as a reservoir for multiple V. cholerae virulence-associated genes which may be exchanged via mobile genetic elements. Therefore, continuous monitoring and genetic characterization of V. cholerae strains in the environment should contribute to the early detection of the sources of infection and prevention of cholera outbreaks as well as to understanding the natural ecology and evolution of V. cholerae.

Cholera returns to southern Vietnam in an outbreak associated with consuming unsafe water through iced tea: A matched case-control study

Background

After more than a decade of steadily declining notifications, the number of reported cholera cases has recently increased in Vietnam. We conducted a matched case-control study to investigate transmission of cholera during an outbreak in Ben Tre, southern Vietnam, and to explore the associated risk factors.

Methodology/Principal findings

Sixty of 71 diarrheal patients confirmed to be infected with cholera by culture and diagnosed between May 9 and August 3, 2010 in Ben Tre were consecutively recruited as case-patients. Case-patients were matched 1:4 to controls by commune, sex, and 5-year age group. Risk factors for cholera were examined by multivariable conditional logistic regression. In addition, environmental samples from villages containing case-patients were taken to identify contamination of food and water sources. The regression indicated that drinking iced tea (adjusted odds ratio (aOR) = 8.40, 95% confidence interval (CI): 1.84–39.25), not always boiling drinking water (aOR = 2.62, 95% CI: 1.03–6.67), having the main source of water for use being close to a toilet (aOR = 4.36, 95% CI: 1.37–13.88), living with people who had acute diarrhea (aOR = 13.72, 95% CI: 2.77–67.97), and little or no education (aOR = 4.89, 95% CI: 1.18–20.19) were significantly associated with increased risk of cholera. In contrast, drinking stored rainwater (aOR = 0.17, 95% CI: 0.04–0.63), eating cooked seafood (aOR = 0.27, 95% CI: 0.10–0.73), and eating steamed vegetables (aOR = 0.22, 95% CI: 0.07–0.70) were protective against cholera. Vibrio cholerae O1 Ogawa carrying ctxA was found in two of twenty-five river water samples and one of six wastewater samples.

Conclusions/Significance

The magnitude of the cholera outbreak in Ben Tre was lower than in other similar settings. This investigation identified several risk factors and underscored the importance of continued responses targeting cholera prevention in southern Vietnam. The association between drinking iced tea and cholera and the spread of V. cholerae O1, altered El Tor strains warrant further research. These findings might be affected by a number of limitations due to the inability to capture asymptomatic or mildly symptomatic infections, the possible underreporting of personal unhygienic behaviors, and the purposive selection of environmental samples.

Cholera is a highly contagious, acute diarrheal illness, which poses a profound health threat in many parts of the less developed world. The majority of cases are reported from Sub-Saharan Africa, South-East Asia, and the Americas (i.e., Haiti) where infections are primarily transmitted through ingestion of contaminated water. Today in the era of widely available rehydration therapies and antibiotics, deaths due to cholera are quite rare. Despite this, early detection of contaminated water sources is crucial for directing early interventions for curbing community-wide transmission. The authors found evidence linking an outbreak of cholera in southern Vietnam to consumption of unsafe water, especially drinking iced tea. This finding suggests the need for a water-monitoring system at ice-making plants. Further research is needed to confirm the biological link between iced tea consumption and cholera infection. Larger studies should also be conducted to understand the clinical consequences of infection with the new cholera agent (V. cholerae O1, altered El Tor strains).