Temperature-dependent Pathogenicity of Acute Hepatopancreatic Necrosis Disease-associated Vibrio strains in Whiteleg shrimp

Acute hepatopancreatic necrosis disease (AHPND) is an economically devastating shrimp disease caused by Vibrio species that are highly temperature-sensitive. However, the correlation between the pathogenicity of AHPND-causing Vibrio species and temperature has not been fully elucidated. This study investigated temperature-dependent pathogenicity (in vivo), bacterial growth kinetics, and virulence gene expression (in vitro). In the bioassay, shrimp challenged with AHPND-causing V. parahaemolyticus (AHPNDVP) and AHPND-causing V. campbellii (AHPNDVC) showed significantly higher mortality (67.6% and 47.1%, respectively) and severe hepatopancreatic necrosis (G4) at low temperatures (20–22°C). In contrast, regardless of temperature, shrimp challenged with AHPND mutant strains with pirAB gene deletions exhibited low or no mortality (0–5.9%) and mild hepatopancreatic degeneration (G1–G2). The bacterial growth kinetics and virulence gene expression of AHPNDVP and AHPNDVC were additionally investigated. AHPNDVP and AHPNDVC were more active at high temperatures (32°C), exhibiting the shortest generation times (16.9 and 17.1 min, respectively) and the highest pirA toxin gene expression (1.34×107 and 4.43×106 copies/μL, respectively). The results revealed that shrimp are more vulnerable to AHPND at low temperatures, while the bacterial growth efficiency and expression of toxin genes of Vibrio species are enhanced at high temperatures. Therefore, to mitigate the impact of AHPND, implementing season-dependent strict management strategies is essential. In summer, environmental improvements are necessary to suppress bacterial proliferation, whereas in winter or transitional seasons, maintaining thermal stability is crucial to protect shrimp from AHPND.