Differentially Expressed Genes in Hepatopancreas of Acute Hepatopancreatic Necrosis Disease Tolerant and Susceptible Shrimp (Penaeus vannamei).

Acute hepatopancreatic necrosis disease (AHPND) is a lethal disease in marine shrimp that has caused large-scale mortalities in shrimp aquaculture in Asia and the Americas. The etiologic agent is a pathogenic Vibrio sp. carrying binary toxin genes, pirA and pirB in plasmid DNA. Developing AHPND tolerant shrimp lines is one of the prophylactic approaches to combat this disease. A selected genetic line of Penaeus vannamei was found to be tolerant to AHPND during screening for disease resistance. The mRNA expression of twelve immune and metabolic genes known to be involved in bacterial pathogenesis were measured by quantitative RT-PCR in two populations of shrimp, namely P1 that showed susceptibility to AHPND, and P2 that showed tolerance to AHPND. Among these genes, the mRNA expression of chymotrypsin A (ChyA) and serine protease (SP), genes that are involved in metabolism, and crustin-P (CRSTP) and prophenol oxidase activation system 2 (PPAE2), genes involved in bacterial pathogenesis in shrimp, showed differential expression between the two populations. The differential expression of these genes shed light on the mechanism of tolerance against AHPND and these genes can potentially serve as candidate markers for tolerance/susceptibility to AHPND in P. vannamei. This is the first report of a comparison of the mRNA expression profiles of AHPND tolerant and susceptible lines of P. vannamei.

A comparative study of Enterocytozoon hepatopenaei (EHP) challenge methods in Penaeus vannamei.

The microsporidium Enterocytozoon hepatopenaei (EHP) is considered as an emerging pathogen threating the shrimp industry worldwide. It is an intracellular parasite that has been associated with retarded growth syndrome and white feces syndrome in shrimp. Although the impact of EHP to the shrimp industry is well known, many aspects of host-pathogen interactions are not well understood. A major limitation in the study of EHP is the lack of a reliable method to produce large quantities of inoculum rapidly and reproducibly. The present study was designed to compare different challenge methods including intramuscular injection, oral administration, co-habitation, hepatopancreas (HP) injection and reverse gavage. The results showed that the HP injection and the reverse gavage are two promising methods to infect shrimp rapidly and generate inoculum in a reproducible manner starting with a limited amount of inoculum. Therefore, the HP injection and reverse gavage were chosen for a scale-up study. Histopathology results showed that EHP proliferated in the epithelial cells of the HP in shrimp challenged via direct injection of inoculum into HP and reverse gavage treatments. In accordance with the histopathology results, the qPCR data showed that EHP loads in the challenged shrimp increased significantly with the HP injection and reverse gavage methods. Furthermore, the histopathological and quantification results indicate that HP injection and reverse gavage are two novel methods that can be used in EHP-challenge studies and for rapidly generating viable EHP inoculum.