Shrimp industry in Thailand with export value over 80 billion baths per year had suffered as much as 25% loss from viral diseases. Effective prevention or treatment of viral infected shrimps is not available. This research group aims to develop an effective means to prevent and protect Peneaus monodon shrimps from yellow head virus (YHV) infection which usually causes high mortality within 3-7 days. In addition, the group aims to create an infrastructure to study RNA interference (RNAi) in shrimp and to apply siRNA technology for prevention of shrimp mortality from YHV infection. This research group found RNAi functioning in shrimp lymphoid cells. The ability of dsRNA to inhibit YHV replication was further investigated and found that dsRNA targeting non-structural genes (protease, polymerase, helicase) were clearly more effective than the structural genes (gp116, gp64). Among the nonstructural genes dsRNA protease was the most effective and able to inhibit YHV replication when injecting into shrimp haemolymp. Injection of dSRNA protease not only inhibited YHV replication but also prevented shrimp mortality. This constitutes the first evidence that shrimp mortality from YHV infection may be prevented by the specific dsRNA through RNAi pathway. The research group cloned essential genes in RNAi pathway (i.e. Argonaute and Dicer) The Argonaute gene encodes 943 a.a. protein whose knock-down impaired RNAi pathway. Two more Argonaute genes whose function is not clear were identified. The cloning and identification of Dicer gene is more complex due to a much larger size. A Dicer gene encoding a minimal 1,786 amino acids was achieved. The gene contained RNA helicase, PAZ, CAT1 and CAT2 RNase III domains and dsRNA binding domain. Development of viral vector for siRNA delivery employed HPV (Hepato pancreatic virus) whose genome sequence was elucidated. Its single-stranded RNA of 6,321 bases has inverted repeats at both 5’ and 3’ temini which presented difficulties to elucidate the structure. To develop HPV infectious clone we faced an obstacle to find an appropriate host for HPV infection in the laboratory. HPV infectious clone has not been achieved. This research group produced 14 international publications with high impact factor and 3 manuscripts. There were 22 researchers; 5 principal investigators, 4 young investigators, 2 Ph.D. students, 9 M.Sc. students and 2 research assistants.