ADJUVANTS IMPROVE THE PROTECTION CONFERRED BY IMMERSION VACCINES AGAINST YERSINIOSIS IN RAINBOW TROUT.

Sophia Xu, Juliette Ben Arous, Laurent Dupuis
 
SEPPIC Inc, 30 Two Bridges Road, Suite 210 - Fairfield, NJ 07004, USA
sophia.xu@airliquide.com

Injection of inactivated vaccines is an effective method to control infectious diseases in aquaculture, and is widely used in fish production. Injection of vaccines in fish is a tedious and costly process. By comparison, vaccination by immersion in a vaccinal bath is a convenient mass vaccination method to administer in one step a preventive cure to a large number of animals with a minimum of handling. It also offers the possibility to vaccinate fish too small to be treated one by one by injection vaccine, and to protect them at very early stage of their life. However, immersion vaccines are usually less effective than injection vaccines. One option to improve the efficacy of immersion vaccines is the addition of relevant adjuvants to vaccine formulations. The present results show that the addition of a micro-emulsion adjuvant improved the immune response and the protection conferred to rainbow trouts by a Yersinia ruckeri whole cell vaccine.  

An adjuvanted immersion vaccine was formulated by mixing inactivated whole cells of a virulent strain of Y. ruckeri (108 cells/ml) with the micro-emulsion adjuvant Montanide™ IMS 1312 VG. 3 groups of 200 healthy rainbow trouts (Oncorhynchus mykiss, 100-120g) were vaccinated by immersion vaccination for 2 min at 12-14°C in a bath containing adjuvanted vaccine, non adjuvanted vaccine (dilution 1/5 in PBS), or no vaccine (control, PBS only). Antibody titers and lyzozyme activity were measured every 2 weeks from 2 to 8 weeks post vaccination. A homologous challenge procedure was performed at 2, 4, 6, 8 and 10 weeks post-vaccination in duplicate. 2x15 fish randomly picked from each group were IP injected with 0.1ml of the virulent strain of Y. ruckeri at 106 cfu/fish and observed for 14 days after challenge.

For 8 weeks post vaccination, lysozyme activity and antibody titers in fish vaccinated with adjuvanted Y. ruckeri vaccine were significantly higher than in fish immunized with non-adjuvanted Y. ruckeri antigen. Lyzozyme activity in control non vaccinated fish was also significantly lower than in both immunized groups. At all dates, the lowest anti-Y. ruckeri antibody titer in vaccinated groups was also significantly higher to antibody titers of the non-vaccinated control group. After challenge procedure, 95-100% of the control fish died. The RPS of fish vaccinated with adjuvanted antigen was 100% at 2 weeks post vaccination and still 94% at 10 weeks post vaccination, whereas the RPS of fish vaccinated with non-adjuvanted antigen reached a maximum of 82%.

These results show that the use of an effective adjuvant can improve the protection conferred by immersion vaccines in trouts. Further studies should be performed to confirm these results in the field.