The protective efficacy of oral delivery of a DNA construct containing the VP28 gene of WSSV encapsulated in chitosan nanoparticles was investigated in black tiger shrimp (Penaeus monodon). The results showed that significant survival was obtained in WSSV-challenged shrimp at 7, 15 and 30 days post-treatment (relative survival, 85%, 65% and 50%, respectively) whereas 100% mortality was observed in the control shrimp fed with feed containing chitosan/pcDNA 3.1 or chitosan/PBS complex. The ability of the chitosan to form a complex with the pVP28 and to stabilize it from endonuclease degradation was studied by agarose gel electrophoresis. Cytotoxicity of chitosan-encapsulated pVP28 was also evaluated by the MTT assay, which showed 90% viability of SISK cells incubated with the pVP28/chitosan complexes. Transcription analysis of the chitosan-encapsulated pVP28 gene in different tissues of DNA-treated shrimp and SISK cell line was confirmed by an RT-PCR reaction. The present study also measured the changes in the level of important immunological parameters such as prophenoloxidase, superoxide dismutase and superoxide anion in hemolymph of chitosan-encapsulated VP28 DNA-treated and controls shrimp. The study also correlated the changes in the level of immunological parameters with the survival percentage and protective efficacy of oral route of DNA construct against WSSV in shrimp. © 2009 Elsevier Ltd. All rights reserved.