To examine the efficacy of the DNA vaccine, the vaccinated and
control groups of fish were challenged with IPNV and monitored for
cumulative mortality. Rainbow trout were divided into three
groups (25 fish each) and were vaccinated by feeding with pellets
containing the encapsulated pcDNA-VP2 plasmid on 3 consecutive
days (10 mg DNA/fish/day: group 1). A second group 2 received
similar amounts of pellets impregnated with the encapsulated
empty pcDNA plasmid and the third group of fish was fed with
commercial pellets. An additional group of fish were vaccinated
individually with a pcDNA.VP2 alginate microspheres solution in
water, and used as a positive control in the light of the results obtained
with this method elsewhere. Water quality was maintained
at optimum levels and all tanks were kept under equivalent conditions.
On day 15 or 30 pv, each group of fish were challenged with
IPNV by immersion (1 106 TCID50 mL1), as described previously
[29]. Fish mortality in each group was subsequently recorded and
any dead fish were removed daily over the next 30 days.
Vaccine efficacy was determined by comparing the average
cumulative percentage of mortality (cpm) and the relative