Translucent post-larvae disease (TPD) is a recently emerged disease in shrimp that poses a major threat to hatcheries, and in grow-out farms, particularly in the first few weeks after stocking ponds with post-larvae. The disease was first discovered in China in 2020 and attracted significant attention due to its potential to cause a large-scale mortality. A highly virulent strain of Vibrio parahaemolyticus, known as Vibrio parahaemolyticus causing TPD (VpTPD), was found to be etiologic agent of the disease.
Previous comparative studies on the pathogenicity of different VpTPD-encoded proteins in post-larvae of P. vannamei, along with mass spectrometry, genomic analysis, epidemiological data and experimental bioassay, identified a novel virulence protein called Vibrio high virulent protein (vhvp), as a potential key virulence factors of the disease. The virulence factor is encoded by the vhvp-2 gene, located on a 187,791 bp plasmid. Further genomic analysis revealed two additional potential virulence genes, vhvp-1 encoding a protein larger than 100 kDa and vhvp-3 encoding another virulent protein about 100 kDa. Both genes are located on the same plasmid.
For nearly four decades, the U.S. aquaculture industry has been the global leader in exporting high quality, healthy, disease-free broodstock and seed stock to aquaculture producers worldwide. Considering the threat that TPD poses to shrimp hatcheries in the US, there is an urgent need to develop TPD-resistant lines in P. vannamei. To investigate the genetic susceptibility of commercially available line of P. vannamei to the disease and explore potential to develop TPD-resistant lines, experimental challenges are being conducted using several family lines at an approximate growth stage of post-larval stage 20 (PL20). After receiving P. vannamei families from various hatcheries across the US, each family line is exposed to V. parahaemolyticus causing TPD via an immersion challenge route at 104 cfu/ml. Mortality data will be collected for each family lines and histopathology will be performed on representative samples. The bacteria load of V. parahaemolyticus in the target organ will be measured using a real-time PCR, targeting the virulence genes, vhvp-1, vhvp-1 and vhvp-3. Comparison of these data among family lines with varying genetic background will help to determine the level of resistance and identify a genetic basis of resistance. The information will be valuable in developing TPD-resistant lines in P. vannamei shrimp by the US shrimp hatcheries.