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Animals play an increasingly important role in society in both the developed and the developing world. In addition, as the global travel of animals, commercial goods and people expands, transmission of disease poses a greater threat than ever before. The demand for animal vaccines must be met in a timely, efficient and economically viable manner. Vaccines for companion animals, which provide for the health and longevity of pets, are generally well established and affordable; the number of companion animals with infectious diseases has decreased significantly since commercial vaccines were made available. Vaccines for livestock are essential for herd health, economic survival of farmers, and the maintenance of trade of meat and other animal products between countries. For livestock, the health of the herd is more important than that of the individual, and the only way to control outbreaks is to cull and mass slaughter herds, resulting in significant economic loss. Vaccination can be an effective preventative measure against infectious diseases; vaccines are therefore required for prophylactic purposes as well as for the control of outbreaks, and need to be affordable on a large scale and easily available. For wildlife, the need is for cheap but effective vaccines that can ideally be consumed orally in the form of bait traps.
DNA vaccines are emerging as a new and important method of vaccination for animals. DNA vaccination involves immunization with a plasmid encoding an antigen of the pathogen. The gene of interest is inserted into a plasmid, along with appropriate genetic elements such as eukaryotic promoters for transcriptional control, a polyadenylation signal sequence for stable and effective translation, and a bacterial origin of replication. The plasmid is transfected into host cells via direct injection, or injection with electroporation or gene gun. The gene of interest then undergoes transcription and translation by host cellular machinery, resulting in the production of an antigenic protein that can induce cellular and humoral immune responses. DNA vaccines have a number of advantages over other vaccination technologies that are of particular interest to veterinary medicine. They have the potential to be less expensive than other commercial vaccines, as they can be produced in large quantities by bacteria and, in the case of certain pathogens, do not require expensive facilities of a high...