Genomic and histopathological characteristics of Vibrio parahaemolyticus isolated from an acute hepatopancreatic necrosis disease outbreak in Pacific white shrimp (Penaeus vannamei) cultured in Korea

This report describes the detailed microbial and histological characteristics of Vibrio parahaemolyticus strains associated with acute hepatopancreatic necrosis disease (Vp_AHPND) that infected Pacific white shrimp (Penaeus vannamei) cultured in Korea. Shrimps showing typical symptoms of AHPND, including a whitish hepatopancreas and empty gut, were reported at two private shrimp farms in Korea in 2019. In the hepatopancreas of the field samples, sloughing of undifferentiated cells in the hepatopancreatic tubule epithelium was observed upon histopathological examination, and 2 Vibrio spp.-related toxin genes (pirA and pirB) associated with AHPND were detected in the samples. Among samples obtained from the hepatopancreas, pond water, and feces (pond sediment), the copy number of the virulent AHPND plasmid was the highest in the hepatopancreas samples, followed by that in the pond water and feces (pond sediment) samples. Two Vp_AHPND strains were isolated from pond water and diseased shrimp. The genome of the virulent AHPND plasmid pVp_Kor-D1–2 (GenBank accession no. CP046414.1), isolated from strain 19–021-D1, was fully sequenced. We confirmed that the Korean Vp_AHPND strain harbored the Asian-type AHPND plasmid, which was almost identical to the AHPND-associated V. owensii plasmid pVOWZ2 previously identified in China. Furthermore, the pathogenicity of the Korean Vp_AHPND strains was evaluated in laboratory bioassays, and we verified that those isolates were highly pathogenic to Pacific white shrimp, causing high cumulative mortality within 3 days.