Temporal Dynamics of pirA Expression During Vibrio campbellii Infection in Litopenaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) is one of the most devastating bacterial diseases affecting Pacific white shrimp (Litopenaeus vannamei) aquaculture worldwide. Although Vibrio parahaemolyticus has been recognized as the principal causative agent of AHPND, increasing evidence indicates that Vibrio campbellii also plays an important role in disease outbreaks. The present study investigated the pathogenicity and temporal dynamics of pirA transcription in V. campbellii isolated from cultured L. vannamei. The isolate was identified by 16S rRNA sequencing, and pirA expression was quantified during bacterial growth under in vitro conditions and throughout experimental infection in vivo using quantitative real-time PCR. In vitro, pirA transcription increased rapidly during the exponential growth phase and reached its highest level at 6 h after incubation, followed by a gradual decline despite continued bacterial growth. Immersion challenge experiments using juvenile shrimp (1 × 106 CFU/mL) resulted in cumulative mortality exceeding 90% within 48 h post-infection. In vivo, pirA transcription remained relatively low during the early stage of infection but increased markedly at 36 h post-infection, coinciding with rapid mortality and severe hepatopancreatic damage. Histopathological examination revealed progressive epithelial cell sloughing, degeneration of B- and F-cells, tubular collapse, and extensive tissue necrosis, which are characteristic lesions of AHPND. These findings demonstrate that V. campbellii possesses strong pathogenic potential. Temporal induction of pirA transcription was closely associated with severe hepatopancreatic lesions and mortality during experimental infection. Collectively, these findings provide new insights into the temporal dynamics of pirA transcription during AHPND progression and its association with tissue pathology and mortality, supporting the development of early molecular diagnostics, disease surveillance, and biosecurity strategies for sustainable shrimp aquaculture.