Infectivity and Transmissibility of Acute Hepatopancreatic Necrosis Disease Associated Vibrio parahaemolyticus in Frozen Shrimp Archived at −80^◦C

Acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus (Vp_AHPND) has been reported in commodity shrimp, but the potential risk of its global spread via frozen shrimp in the shrimp trade is yet to be fully explored. We hypothesized that frozen shrimp with AHPND could be a source of Vp_AHPND transmission; thus, the infectivity of frozen shrimp with AHPND was evaluated using a shrimp bioassay. To prepare infected frozen shrimp, 12 Penaeus vannamei (average weight, 2 g) were exposed to Vp_AHPND by immersion in water with a Vp_AHPND concentration of 1.55 × 10⁷ CFU mL⁻¹; once dead, the shrimp were stored at −80^◦C for further analysis. After two weeks, a PCR assay was used to confirm AHPND positivity in frozen shrimp (n = 2), and Vp_AHPND was reisolated from the hepatopancreases of these shrimp. For the infectivity test, 10 P. vannamei (average weight, 4 g) were fed with the hepatopancreases of Vp_AHPND-infected frozen shrimp (n = 10). After feeding, 70% of the shrimp died within 118 h, and the presence of Vp_AHPND was confirmed using a PCR assay and histopathology examination; moreover, Vp_AHPND was successfully reisolated from the hepatopancreases of the dead shrimp. We are the first to evaluate the potential transmissibility of Vp_AHPND in frozen shrimp, and our results suggest that frozen shrimp with AHPND are a potential source of disease spreading between countries during international trade.