Characteristics and diversity of Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease in Vietnam

Acute hepatopancreatic necrosis disease (AHPND) is a contagious disease in shrimp with extremely high mortality rate, causing an estimated $23.6 billion loss to the global shrimp industry during 2009–2016. A binary toxin, PirAB, is the causative agent, which is encoded by the pirAB^vp genes on a virulent plasmid typically found in Vibrio parahaemolyticus. Here, seventeen strains of V. parahaemolyticus were isolated from the Mekong Delta of Vietnam, of which 15 harboured identical pirAB^vp genes. The remaining two strains, which were PCR-negative for pirAB, and nine positive strains were selected for whole genome sequencing. Multi-locus sequence typing revealed five sequence types (STs), including one novel, that were associated with sites of isolation. A maximum likelihood tree of core genomes revealed that our strains formed three clusters and were closely related to strains from Thailand, South Korea, China, and Philippines. All sequenced strains carried β-lactam (including bla_OXA-10 and bla_NDM-1) and tetracycline resistance genes, with a range of 3–13 resistance genes. The pirAB-positive strains shared large regions of homology with the prototypical AHPND virulent plasmid. In summary, this work revealed the characteristics of AHPND-causing strains in the Mekong Delta of Vietnam and suggested possible transmission routes among Vietnam and other shrimp farming countries.