Cationic liposome–DNA complexes (CLDC) are cationic/neutral lipid carriers complexed with plasmid DNA that when administered systemically results in a robust TH1 cytokine response. CLDC have been shown to be effective in prophylaxis and therapeutic treatment of animal models of viral disease. To determine the contribution of liposomal delivery and CpG content of the plasmid DNA to the efficacy of CLDC; plasmid, CpG-free plasmid DNA, or CpG-containing oligodeoxynucleotides (ODN) with and without liposomes, as well as poly(I:C12U), were evaluated for their ability to elicit protection against lethal Punta Toro virus (PTV, Bunyaviridae, phlebovirus) challenge in hamsters. CLDC-containing plasmid significantly improved survival, decreased systemic and liver viral loads, and reduced liver damage due to progression of viral infection. Mouse-reactive ODNs complexed with liposomes failed to protect hamsters, whereas ODNs known to cross-react with human and mouse (CpG 2006) or non-liposomal poly(I:C12U) showed survival benefit but did not limit liver injury. Liposomes complexed with a non-CpG motif-containing plasmid reduced liver viral load and tissue damage, but did not protect hamsters from death. To evaluate the mechanisms of the enhanced activity of CLDC, microarray experiments examined differences in the gene expression profile. The results suggest a broad TH1 response elicited by liposomal delivery of a diverse sequence containing CpG and non-CpG elements may be a more effective antiviral treatment than other nucleic acid based immunotherapeutics.