Oral DNA vaccination of rainbow trout, Oncorhynchus mykiss (Walbaum), against infectious haematopoietic necrosis virus using PLGA [Poly(D,L-Lactic-Co-Glycolic Acid)] nanoparticles M Adomako 1 , S St-Hilaire 1 , Y Zheng 2 , J Eley 2 , R D Marcum 1 , W Sealey 3 , B C Donahower 3 , S LaPatra 4 and P P Sheridan 1 1 Department of Biological Sciences, College of Art and Science, Idaho State University, Pocatello, ID, USA 2 Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, Pocatello, ID, USA 3 Hagerman Fish Culture Experiment Station, University of Idaho, Hagerman, ID, USA 4 Research Division, Clear Springs Foods, Inc., Buhl, ID, USA Abstract A DNA vaccine against infectious haematopoietic necrosis virus (IHNV) is effective at protecting rainbow trout, Oncorhynchus mykiss, against disease, but intramuscular injection is required and makes the vaccine impractical for use in the freshwater rainbow trout farming industry. Poly (D,L-lactic-co- glycolic acid) (PLGA) is a U.S. Food and Drug Administration (FDA) approved polymer that can be used to deliver DNA vaccines. We evaluated the in vivo absorption of PLGA nanoparticles contain- ing coumarin-6 when added to a fish food pellet. We demonstrated that rainbow trout will eat PLGA nanoparticle coated feed and that these nanoparti- cles can be detected in the epithelial cells of the lower intestine within 96 h after feeding. We also detected low levels of gene expression and anti- IHNV neutralizing antibodies when fish were fed or intubated with PLGA nanoparticles containing IHNV G gene plasmid. A virus challenge evaluation suggested a slight increase in survival at 6 weeks post-vaccination in fish that received a high dose of the oral vaccine, but there was no difference when additional fish were challenged at 10 weeks post- vaccination. The results of this study suggest that it is possible to induce an immune response using an orally delivered DNA vaccine, but the current sys- tem needs improvement. Keywords: DNA vaccine, infectious haematopoietic necrosis virus, PLGA, rainbow trout. Introduction Infectious haematopoietic necrosis virus (IHNV) is a major pathogen of rainbow trout, Oncorhynchus mykiss (Walbaum), that can cause mortality rates as high as 90%, depending on environmental condi- tions and the size of the fish (Purcell, LaPatra, Woodson, Kurath & Winton 2010). This virus, first reported in anadromous salmonids, was recognized in rainbow trout in British Colombia in 1967 (Amend 1975). Currently, IHNV is endemic in a range of salmonid species in the western United States and adversely affects public and private aquaculture in North America, Asia and Europe (Nichol, Rowe & Winton 1995; Schu ¨tze, Enzmann, Kuchling, Mundt, Niemann & Mettenleiter 1995). Currently, avoidance of infection is the only method available for controlling IHN in the United States, because there are no approved therapeutics for viral infections in fish. In Canada, a vaccine called Apex-IHN Ò has been approved for use in Atlantic salmon, Salmo salar L., (Tonheim, Bøgwald & Dalmo 2008), and laboratory trials (Corbeil, LaPatra, Anderson, Jones, Vincent, Hsu Journal of Fish Diseases 2012, 35, 203–214 doi:10.1111/j.1365-2761.2011.01338.x Correspondence S St-Hilaire, Department of Health Manage- ment, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PEI Canada C1A 4P3 (e-mail: ssthilaire@ upei.ca) 203 Ó 2012 Blackwell Publishing Ltd