1. Introduction
The control of infectious diseases is essential to maintain the
levels of productivity in the aquaculture industry. The economic
impact of infectious diseases, particularly those of viral aetiology, is
a constant worldwide threat in the salmonid fish industry, stimulating
research to find efficient methods to minimize such losses.
Vaccination is the most effective approach to combat disease in
aquaculture, a strategy that is ideal to prevent and avoid the
dispersion of infective viruses in fish, particularly in farms where
fish are raised under intensive culture conditions. Although
different types of viral vaccines have been described for fish,
including inactivated, attenuated, synthetic peptides or subunit
vaccines [1e3], protection is not always complete. Hence, studies
are necessary to produce improved vaccines capable of inducing
longer lasting immunity and less stressful methods of administration
[4]. Genetic vaccines were first developed for mammals in the
1990s and several designs to protect against rhabdoviruses have
been tested in salmonid fish species [5e12]. More recently, other
DNA vaccines have been described to combat the infectious pancreatic necrosis virus (IPNV), another viral pathogen of
salmonid fish