LETTER
Vibrio cholerae, the causative agent of cholera, is endemic in many areas of the world. The V. cholerae serogroup O1, consisting of two biotypes (classical and El Tor), and the derivative serotype O139 can cause epidemics of cholera. V. cholerae O139 first emerged in South India during 1992, and subsequently in Bangladesh and China in 1993 (1). Three V. cholerae O139 isolates were reported from Bangladesh (2013 to 2014) (2), and 37 were reported from China (2013) (3). V. cholerae O139 isolates were reported for the first time in 1995 (4), and the last report was in 2006 (5), from Odisha. A large outbreak of severe watery diarrhea reported on 2 May 2017 from Belabahali village, Anandapur block, Keonjhar District, was investigated to find out the causative organism.
The village is located at the bank of Kosei River (Fig. 1), and the water supply of the village was directly through a borewell pipe submerged in the river. The index case was a 75-year-old female who was suffering from rice-watery stool, vomiting, abdominal cramping, and muscular pain on 30 April 2017. There was torrential rainfall for about 5 h on 1 May 2017. Suddenly, 18 severe watery diarrhea cases were reported on 2 May 2017; 67 diarrhea cases and no deaths were reported from 30 April 2017 to 11 May 2017. Twenty rectal swabs and 11 water samples, including the starting supply water point, were processed per our previous practice (5). Fifteen (75%) out of 20 rectal swabs and one out of 11 water samples were positive for the V. cholerae O139 serogroup. V. cholerae O139 strains were resistant to ampicillin and streptomycin only. The selected V. cholerae O139 strains were subjected to double-mismatch-amplification mutation assay (DMAMA) PCR assay, sequencing, and pulsed-field gel electrophoresis (PFGE) analysis (6). The DMAMA PCR assay of the ctxB gene of all V. cholerae O139 isolates indicated that all were negative for ctxB7 of Haitian variant V. cholerae; however, sequencing of the ctxB gene indicated that both the clinical and water isolates of V. cholerae O139 were prototype El Tor ctxB with a single mutation at position 132 of the amino acid sequence and the cysteine substituted by glutamine, therefore indicating a new genotype (GenBank accession number MH423442). The PFGE result for selected V. cholerae O139 strains, including the water isolate, indicated that there were three different pulsotypes (Fig. 2).
FIG 1.
Map showing cholera outbreak village, Anandapur block, Keonjhar district.
FIG 2.
PFGE patterns of the NotI-digested V. cholerae O139 strains (clinical isolates BS2, BS3, BS5 BS9, BS19, and BS20; water isolate BW 11) from Odisha and the SG 24 (standard V. cholerae O139) strain, along with dendrogram analysis using BioNumerics software (Applied Maths, Sint-Martens-Latem, Belgium). Analysis showed 3 distinct pulsotypes, suggesting 90% similarity with the standard strain.
Torrential rainfall for 5 h on 1 May 2017 and a contaminated muddy water supply to the village were the major source of infection. The first emergence of V. cholerae O139 was reported in 1995 from Odisha (5). The V. cholerae O139 strains isolated in Bangladesh from 1993 to 2005 were 3 new ctxB genotypes, closely similar to ctxB El Tor (7), and were completely different from the present findings.
Three interesting findings emerged from this investigation, namely (i) the reemergence of V. cholerae O139 in Odisha after a hiatus of 10 years; (ii) the reemerged O139 strains carried a novel ctxB genotype, and this is the first report of such strains of O139 causing outbreaks of cholera; and (iii) a new variant of V. cholerae O139 has again emerged from the Bay of Bengal region (7). By sequencing and comparing hundreds of bacterial genomes, recent studies have shown that all of the explosive epidemics of cholera in Africa and the Americas in the past half-century arose after the arrival of new strains that had evolved in Asia (8, 9). Although the O139 serotype of V. cholerae has not spread to the African or American continents, the likelihood of this new variant spreading to other parts of the world should not be underestimated.
ACKNOWLEDGMENTS
We thank S. Pati, Director, Regional Medical Research Centre (ICMR), Bhubaneswar, for her support; S. S. Bal, ADMO (PH), CDMO office, Keonjhar, for cooperation and sample collection; and G. B. Nair and T. Ramamurthy for their valuable suggestions. We also acknowledge the PFGE analysis rendered by D. V. Singh, Institute of Life Science, Bhubaneswar.
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