Evolutionary perspective on the origin of Haitian cholera outbreak strain

Cholera epidemic has not been reported in Haiti for at least 100 years, although cholera has been present in Latin America since 1991. Surprisingly, the recent cholera epidemic in Haiti (October 2010) recorded more than 250,000 cases and 4000 deaths in the first 6 months and became one of the most explosive and deadly cholera outbreak in recent history. In the present study, we conducted genomic analyses of pathogenicity islands of three Haitian Vibrio cholerae strains and compared them with nine different V. cholerae O1 El Tor genomes. Although CIRS101 is evolutionarily most similar to the Haitian strains, our study also provides some important differences in the genetic organization of pathogenicity islands of Haitian strains with CIRS101. Evolutionary analysis suggests that unusual functional constraints have been imposed on the Haitian strains and we hypothesize that amino acid substitution is more deleterious in Haitian strains than in nonHaitian strains.