Department af Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran- Iran
BACKGROUND: Outbreak and development of yersiniosis in rainbow trout farms in Iran has caused a serious problem over the last years. Objectives: The purpose of this study was to evaluate the efficacy of immersion vaccination with Yersinia ruckeri in rainbow trout. Methods: Prior to antigen preparation, the phenotypic, molecular and serological features of a number of Yersinia ruckeri isolates obtained from affected trout farms were studied. The virulent of these isolates were then evaluated using intra peritoneal injection route. Trout were vaccinated by immersion route (3 min at 12 °C) using Yersinia ruckeri bacterin of the virulent strains. The efficacy of vaccine antibody titer within 2, 4, 6, 8 and 10 weeks post vaccination were evaluated using relative percent survival. Results: The phenotyping, serological and molecular studies have led to identification of 8 isolates of Yersinia ruckeri and all the isolates produced bands 409 bp, which is indicative of Yersinia ruckeri. In pathogenicity test 3 isolates caused above 50% mortality, while 5 isolates reached 16%. The RPS of vaccinated fish reached 72.7, 80, 80, 82.2 and 83.3% within 2, 4, 6, 8 and 10 weeks post vaccination, respectively. In the other words, the mortality level in vaccinated groups was in range of 10-20% within 10 weeks post vaccination, while those of control group was in range 56.7 - 73.3% (p<0.05) .The lowest and the highest antibody titers in immunized groups were 32±4.50 and 164.57±9.37 respectively, obtained after 4 and 10 weeks of immunization, whereas the control group had no measurable titer of antibody. Conclusions: The results of this study clearly show that this vaccine can remarkably protect the trout from yersiniosis outbreaks inside Iran.