Effect of florfenicol on the immune response of rainbow trout (Oncorhynchus mykiss)

Florfenicol, a drug effective against several bacterial diseases of fish, w as tested for possible immunomodulatory effects. The aim of the study was t o follow the kinetics of the immune response after Vaccination with simulta neous oral antibiotic treatment. The fish were immunised with a commercial oil-based divalent (furunculosis/vibriosis) vaccine and were simultaneously given oral antibiotic treatment. The specific immune response was monitore d by analysing the levels of specific antibodies with ELISA. As an indicato r of the non-specific immune response the phagocytic activity of circulatin g leucocytes was measured by a chemiluminescence assay. Total circulating l eucocyte counts and differentials were also monitored. The disease resistan ce was evaluated by challenge tests at the end of the experiment. The resul ts showed that florfenicol did not have any significant effect on antibody production and circulating leucocyte levels but caused a suppression in che miluminescence response/phagocytic cell 5-6 weeks after vaccination. The su rvival after challenge was slightly suppressed by the florfenicol treatment . The RPS-value for the vaccinated group was 98% and for the fIorfenicol-tr eated group was 88%. (C) 1999 Elsevier Science B.V. All rights reserved.