White spot syndrome virus and Vibrio parahaemolyticus challenge model development in whiteleg shrimp (Litopenaeus vannamei)
Shrimp aquaculture is a 38 billion dollar (USD) global industry, with whiteleg shrimp (Litopenaeus vannamei) accounting for approximately 80% of production. Due to the intense nature of shrimp aquaculture, disease outbreaks can have major impact. Pathogens of concern include white spot syndrome virus (WSSV), and Vibrio parahaemolyticus , the aetiological agent of acute hepatopancreatic necrosis disease (AHPND), both of which have been reported to cause mortality up to 80-100%. No current treatments are available for WSSV, and reduced efficacy of antibiotic treatments for V. parahaemolyticus due to development of resistance, together with a negative market opinion on their use, has led the industry to seek novel treatment strategies. To facilitate research into the efficacy of novel disease treatments in whiteleg shrimp, challenge models for WSSV and V. parahaemolyticus were developed.
In these challenge model development experiments, methods were established to prepare the WSSV inoculum, and bacterial culture growth conditions were optimized for V. parahaemolyticus . In addition, the dose-response relationship and the effect of shrimp size on mortality were characterized.
Per os and intraperitoneal injection challenge models for WSSV, and a per os challenge model for V. parahaemolyticus were established. Although the challenge models were initially developed for challenge of individual shrimp housed in separate tanks, experiments showed that these models translate well to population-based challenges. These allow a larger number of shrimp to be challenged, increasing the statistical robustness of the study. When testing the efficacy of treatments expected to have a moderate protective effect (e.g. a relative percent survival of 20-40% as observed in some functional feed studies), use of a population-based challenge increases the likelihood to detect a significant effect of the treatment