Evidence for a clonally different origin of the two cholera epidemics of 2001-2002 and 1980-1987 in South Africa.

Vibrio cholerae O1 serotype Ogawa and serotype Inaba isolates from the cholera epidemic that occurred in 2001 and 2002 in South Africa were compared with isolates of V. cholerae O1 serotype Inaba from the epidemic that occurred between 1980 and 1987. PFGE using NotI digestion was used to compare stored isolates received during the 1980s epidemic with those received during the epidemic in 2001/2002. A selected number of these isolates were then sequenced to compare the sequence of the wbeT gene in the V. cholerae O1 Ogawa strains of 2001/2002 with that in the V. cholerae O1 Inaba strains of the 1980s and 2001/2002. Isolates from the recent epidemic were shown to be related, irrespective of serotype, and had comparable banding patterns on PFGE, using NotI. They were distinctly different from those from the previous epidemic. Sequencing of the wbeT gene showed that the gene was highly conserved between the two epidemics. A single deletional mutation of an adenine residue was observed in the V. cholerae serotype Inaba isolates from the 2001/2002 epidemic, resulting in the serotype switch between the V. cholerae O1 strains from the recent epidemic. The distinct differences in PFGE patterns among isolates from the first and second epidemics exclude the possibility that the Inaba strain from the 1980s became dormant in the environment and mutated to serotype Ogawa, causing the 2001/2002 epidemic, despite the apparent consistency in the site of mutation in the Inaba serotypes between the two epidemics.