Vibrio parahaemolyticus carrying a plasmid encoding toxins PirA and PirB is one of the causative agents leading to the severe disease of acute hepatopancreatic necrosis disease (AHPND) in shrimp aquaculture. However, there is a lack of deep understanding of the host resistant characteristics against V. parahaemolyticus infection. Here, we performed comparative transcriptome analysis on the expression profiles at the background level of hemocytes from shrimp with different resistant abilities against V. parahaemolyticus infection in two independent populations. Principal component analysis and sample clustering results showed that samples from the same population had a closer relationship than that from shrimp with similar disease-resistant abilities. Differentially expressed genes (DEGs) analysis revealed that the number of DEGs between two populations was much more than that between V. parahaemolyticus¬-resistant and susceptible shrimp. A total of 31 DEGs and 5 DEGs were identified from the comparison between V. parahaemolyticus¬-resistant and susceptible shrimp from population 1 and 2, respectively. There was no DEGs overlap between two comparisons. DEGs from population 1 were mainly cytoskeleton related genes, metabolic related genes, and immune related genes. DEGs from population 2 included tubulin alpha-3, dihydropyrimidinase-like gene, diacylglycerol kinase 1, prohibitin and iroquois-class homeodomain protein IRX-2-like. The data suggest that shrimp from different populations might adopt distinct disease-resistant mechanisms, which provided new insights into understanding disease-resistant mechanisms at population level against pathogen infection. A new strategy for screening disease resistant genes and disease resistant breeding was proposed based on the present study.

In this study, ridgetail white prawns Exopalaemon carinicauda were infected per os with debris of Shrimp hemocyte iridescent virus (SHIV)-infected Penaeus vannamei and via intramuscular injection (im) with raw extracts of SHIV. The infected E. carinicauda showed obvious clinical symptoms, including weakness, empty gut and stomach, pale hepatopancreas, and partial death with cumulative mortality of (50.0±26.5)% and (76.7±18.3)%, respectively. Results of TaqMan probe based real-time quantitative PCR showed that the moribund and survival individuals with clinical signs of infected E. carinicauda were SHIV-positive. Histological examination showed that there were dark eosinophilic inclusions, of which some were surrounded with or contained tiny basophilic staining, and pyknosis in cytoplasm of hemocytes in the hepatopancreatic sinus, hematopoietic cells, and cuticular epithelium, etc. Positive hybridization signals were observed in stomach, hematopoietic tissue, cuticular epithelium, and hepatopancreatic sinus of infected prawns from both per os and im groups, according to the results of in situ DIG-labeling-loop-mediated DNA Amplification (ISDL). Transmission electron microscopy of ultrathin sections showed that icosahedral SHIV particles existed in hepatopancreatic sinus and gills of the infected E. carinicauda of the per os group. The viral particles were also observed in the hepatopancreatic sinus, gills, pereiopods, muscles, and uropods of the infected E. carinicauda from the im group. The assembled virions mostly distributed outside of the assembling area near cellular membrane of infected cells, which were with envelope and about 150 nm in diagonal diameter. The results of molecular biological tests, histopathological examination, ISDL, and transmission electron microscopy confirmed that E. carinicauda is one of the susceptible hosts of SHIV. This study also reminded that E. carinicauda showed some degree of tolerance to the infection with SHIV per os challenge mimicking natural pathway.