Immunomodulatory responses and mitigation of Vibrio parahaemolyticus infection in white shrimp induced by heat-killed Vibrio parahaemolyticus

This study investigated the immunoprotective efficacy of heat-killed Vibrio parahaemolyticus (HVp) at two concentrations, 1 × 10 5 CFU/mL (HVp5) and 1 × 10 7 CFU/mL (HVp7), administered via intramuscular injection in Litopenaeus vannamei . Immune parameters, carbohydrate metabolism, bacterial clearance efficiency, histopathology, and survival following pathogen challenge were comprehensively evaluated. HVp5 and HVp7 significantly enhanced innate immune responses, including elevated total and differential haemocyte counts, increased phenoloxidase and respiratory burst activities, heightened lysozyme levels, and improved phagocytic and bacterial clearance capacities. The immune responses were maintained over seven days, demonstrating effective immune priming. Furthermore, HVp-treated shrimp demonstrated more stable glucose and lactate profiles than shrimp injected with live V. parahaemolyticus , indicating improved energy regulation, and reduced metabolic disruption. The metabolic stability and immunological activation show that heat-killed bacteria are good immunostimulants that are safe to apply. The HVp5 and HVp7 groups showed significantly higher survival rates (66.67% and 70.83%, respectively) after exposure to the disease than the unimmunized control group (45.83%). A histological study supported the results even more. It demonstrated that the hepatopancreas tissue of the shrimp treated with HVp was mainly healthy, while the control group had extensive epithelial damage, which indicates V. parahaemolyticus pathology.