Pathogenesis and genome characterization of translucent post-larvae disease-causing Vibrio parahaemolyticus in Litopenaeus vannamei.

Emerging infectious diseases threaten shrimp aquaculture, causing economic losses and challenging disease preparedness. Translucent Post-larvae Disease (TPD) is associated with Vibrio parahaemolyticus strains harboring a virulence plasmid encoding Vibrio high virulent proteins (VHVP). TPD causes translucent or pale body coloration, and high mortality. In this study, shrimp exhibiting TPD-like signs were obtained from local farms. A pathogenic V. parahaemolyticus strain (P40) was isolated from cephalothorax homogenates and screened for TPD-associated virulence genes (vhvp1, vhvp2-1, and vhvp2-2) by colony PCR. Immersion challenge assays confirmed the pathogenicity of strain P40, reproduced TPD signs and high mortality. A single-colony isolate designated P40.49, was used for subsequent analyses. Based on quantitative PCR (qPCR) analysis, stomach, hepatopancreas, and intestine were primary tissues for early detection of TPD-associated bacterial genome copies. Histopathological examination demonstrated epithelial sloughing, necrosis and hemocytic infiltration in both hepatopancreas and intestine. TPD infection significantly modulated host responses, including upregulation of innate immune genes (proPO, PPAE1, Toll-like, Serpin7, and Pen3a) and antioxidative response genes (MnSOD2 and ROS modulator). Dietary supplementation with perilla powder attenuated TPD-associated clinical manifestations and reduced detection of vhvp genes in stomach tissue. Whole-genome sequencing confirmed a TPD-associated virulence plasmid, and phylogenetic analysis clustered the strain with reported TPD isolates from China and Southeast Asia. Comparative genomic analysis further identified four unique plasmid-associated genes specific to TPD-causing strains and infected samples, suggesting their potential as additional molecular markers for TPD diagnosis. These findings provided mechanistic insights into TPD pathogenesis and support improved diagnostics, nutritional and biosecurity strategies for sustainable shrimp aquaculture.