Vibrio parahaemolyticus is a foodborne pathogen that has become a public health concern at the global scale. The epidemiological significance of V. parahaemolyticus infections in Latin America received little attention until the winter of 1997 when cases related to the pandemic clone were detected in the region, changing the epidemic dynamics of this pathogen in Peru. With the aim to assess the impact of the arrival of the pandemic clone on local populations of pathogenic V. parahaemolyticus in Peru, we investigated the population genetics and genomic variation in a complete collection of non-pandemic strains recovered from clinical sources in Peru during the pre- and post-emergence periods of the pandemic clone. A total of 56 clinical strains isolated in Peru during the period 1994 to 2007, 13 strains from Chile and 20 strains from Asia were characterized by Multilocus Sequence Typing (MLST) and checked for the presence of Variable Genomic Regions (VGRs). The emergence of O3:K6 cases in Peru implied a drastic disruption of the seasonal dynamics of infections and a shift in the serotype dominance of pathogenic V. parahaemolyticus. After the arrival of the pandemic clone, a great diversity of serovars not previously reported was detected in the country, which supports the introduction of additional populations cohabitating with the pandemic group. Moreover, the presence of genomic regions characteristic of the pandemic clone in other non-pandemic strains may represent early evidence of genetic transfer from the introduced population to the local communities. Finally, the results of this study stress the importance of population admixture, horizontal genetic transfer and homologous recombination as major events shaping the structure and diversity of pathogenic V. parahaemolyticus.
Infections caused by Vibrio parahaemolyticus have increased significantly over the last two decades, with cases now regularly reported globally. The emergence of cholera at global scale has brought the attention toward other Vibrio diseases in developing countries. This was the situation in Peru, where the investigation of V. cholerae in hospitals and regional public health laboratories after the dramatic emergence of cholera epidemic in 1991 enabled the identification of other pathogenic Vibrio throughout the whole country. The submission of all these bacteria to the Instituto Nacional de Salud (INS, Lima, Peru) for characterization generated an extraordinary repository of records and isolates which have been decisive for sizing the impact of V. parahaemolyticus infections on the population. The present study addresses, for first time, the impact of the arrival of a non-endemic population of V. parahaemolyticus on the genetic structure and virulence attributes of local populations. The detection of the pandemic clone of V. parahaemolyticus to Peru in 1997 changed not only the epidemic dynamics of this pathogen, but also the population structure and genetic variation of native populations through population admixture, horizontal genetic transfer and homologous recombination between native and introduced populations of pathogenic V. parahaemolyticus.