Abstract
The world's worst cholera epidemic in Haiti (2010) coerced to trace the origin and dissemination of the causative agent Vibrio cholerae O1 for proper management of cholera. Sequence analysis of the Haitian strain showed several variations in the genes encoding cholera toxin B subunit (ctxB); toxin-co-regulated pilus (tcpA), repeat in toxins (rtxA), quinolone resistance-determining region (QRDR) of gyrase A (gyrA), rstB of RS element along with the change in the number of repeat sequences at the promoter region of ctxAB. Our earlier studies showed that variant tcpA (tcpA CIRS) and ctxB (ctxB7) first appeared in Kolkata during 2003 and 2006, respectively. The present study revealed that a variant rtxA was first isolated in Kolkata during 2004 and probably formed the genetic background for the emergence of the ctxB7 allele as we were unable to detect a single strain with the combination of El Tor rtxA and ctxB7. The variant gyrA was first time detected in Kolkata during 1994. The Kolkata strains contained four heptad repeats (TTTTGAT) in their CT promoter regions whereas Haitian strains carried 5 heptad repeats. Haitian strains had 3 nucleotide deletions at the rstB gene, which is a unique feature of the classical biotype strains. But the Kolkata strains did not have such deletion mutations in the rstB. Our study demonstrated the existence of some Haitian genetic traits in Kolkata isolates along with the dissimilarities in genomic content with respect to rstB and ctxAB promoter region. Finally, we conclude that Haitian variant strain may be evolved due to sequential event in the Indian subcontinent strain with some cryptic modification in the genome.
Highlights
Cholera is still a considerable health burden due to poor hygiene and sanitation in developing countries, especially in Africa and Asia
All the V. cholerae strains in Kolkata had classical cholera toxin B subunit (ctxB) with El Tor tcpA up to September 2003
Our previous study indicated that the variant tcpA and ctxB first appeared in Kolkata during October 2003 and April 2006, respectively [4, 23]
Summary
Cholera is still a considerable health burden due to poor hygiene and sanitation in developing countries, especially in Africa and Asia. This severe, dehydrating diarrheal disease is triggered by the Gram negative bacterium Vibrio cholerae. The devastating cholera outbreak during 2010 in Haiti, for the first time in almost a century, placed this ancient scourge at the forefront of the global public health agenda [8]. In this outbreak, more than 500,000 were infected and around 8000 people died. The World Health Organization, in May 2011, documented the re-emergence of cholera as a substantial global public health problem and asked for the execution of an integrated and inclusive global approach to control the cholera [12]
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