Abstract
ABSTRACTVibrio parahaemolyticus is the leading cause of seafood-related infections with illnesses undergoing a geographic expansion. In this process of expansion, the most fundamental change has been the transition from infections caused by local strains to the surge of pandemic clonal types. Pandemic clone sequence type 3 (ST3) was the only example of transcontinental spreading until 2012, when ST36 was detected outside the region where it is endemic in the U.S. Pacific Northwest causing infections along the U.S. northeast coast and Spain. Here, we used genome-wide analyses to reconstruct the evolutionary history of the V. parahaemolyticus ST36 clone over the course of its geographic expansion during the previous 25 years. The origin of this lineage was estimated to be in ~1985. By 1995, a new variant emerged in the region and quickly replaced the old clone, which has not been detected since 2000. The new Pacific Northwest (PNW) lineage was responsible for the first cases associated with this clone outside the Pacific Northwest region. After several introductions into the northeast coast, the new PNW clone differentiated into a highly dynamic group that continues to cause illness on the northeast coast of the United States. Surprisingly, the strains detected in Europe in 2012 diverged from this ancestral group around 2000 and have conserved genetic features present only in the old PNW lineage. Recombination was identified as the major driver of diversification, with some preliminary observations suggesting a trend toward a more specialized lifestyle, which may represent a critical element in the expansion of epidemics under scenarios of coastal warming.
Highlights
Vibrio parahaemolyticus is the leading cause of seafood-related infections with illnesses undergoing a geographic expansion
To investigate the evolutionary changes that characterized the epidemic expansion of V. parahaemolyticus sequence type 36 (ST36), we sequenced 44 strains from different geographic areas on the Pacific and Atlantic coasts of the United States previously recovered from sporadic cases and outbreaks, including the ST36 strains recovered from the single outbreak in the northwest of Spain in 2012 [17]
The remaining 214 variable sites were found in noncoding regions (576,056 bp), which represented twice the rate of SNPs found in coding regions
Summary
Vibrio parahaemolyticus is the leading cause of seafood-related infections with illnesses undergoing a geographic expansion. We used genome-wide analyses to reconstruct the evolutionary history of the V. parahaemolyticus ST36 clone over the course of its geographic expansion during the previous 25 years The origin of this lineage was estimated to be in ~1985. While the current pandemic of V. cholerae emerged more than 50 years ago, the global expansion of V. parahaemolyticus is a recent phenomenon These modern expansions provide an exceptional opportunity to study the evolutionary process of these pathogens at first hand and gain an understanding of the mechanisms shaping the epidemic dynamics of these diseases, in particular, the emergence, dispersal, and successful introduction in new regions facilitating global spreading of infections. V. parahaemolyticus is the most prevalent food poisoning bacterium associated with seafood consumption in many regions globally, typically causing acute gastroenteritis This bacterium grows preferentially in warm (Ͼ15°C), low-salinity (Ͻ25 ppt NaCl) marine water [5]. Future climate scenarios based on climate modeling suggest that Vibrio spp., including V. parahaemolyticus, are likely to continue to pose a significant and expanding public health risk
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