PD-Vaccination - Effect of Different Vaccines for Induction of Circulating Antibodies

Abstract

In this thesis we have examined different PD-vaccines’ capability to induce circulating and neutralizing antibodies in Atlantic salmon. We have tried to compare the level of circulating and neutralizing antibodies from fish vaccinated with the DNA-vaccine Clynav and the whole virus inactivated vaccine AlphaJect Micro 1 PD, and the combination of these when injected at the same time. To detect the presence and level of circulating antibodies in the plasma samples, we used an indirect ELISA method. The results showed that the DNA vaccine induced the highest level of circulating antibodies, but there was a variation within the group. The AlphaJect Micro 1 PD vaccine gave a lower level of circulating antibodies, and with less variation within the group. When the two vaccines were combined, immunized fish had a low level of circulating antibodies. We also used a control group that was obtained from the field, vaccinated with the inactivated whole virus vaccine named Aquavac PD7 (MSD), which was also detected with circulating antibodies in the ELISA, but the level of antibodies in the group was more dispersed than in the other groups. We cultured CHH1-cells and inoculated them with SAV-3, and then detected CPE. We then performed a virus titration to find the TCID50, which was then used for the virus neutralization test. The virus neutralization test had invalid results, with all wells containing plasma from the different vaccine groups having a positive effect on CPE. Negative and positive control were as expected. Sources of error in the failed virus neutralization test may include not optimal plasma storage that may have damaged the antibodies, presence of some dead viruses in the supernatant used, and incorrect well row readings that were then used to calculate TCID50. Based on the outcome of our studies, we can only conclude that there is a presence of circulating antibodies in the different vaccines and in the combination of the two, at different levels. The DNA-vaccinated individuals had the highest level of circulating antibodies detected, while the combination-vaccinated individuals had the lowest level of circulating antibodies detected in the ELISA test. We can not say whether the antibodies are neutralizing or not, based on our failed virus neutralization result.