TWENTY-THIRD ANNUAL EASTERN FISH HEALTH WORKSHOP JOHN CARVER INN, PLYMOUTH, MA 30 MARCH - 2 APRIL, 1998 Vaccination Of Channel Catfish (Ictalurus punctatus) Against Ichthyopthirius multifiliis Using A Subunit Vaccine Xuting Wang and Harry W. Dickerson Department of Medical Microbiology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7371 Fish surviving mild infections with the parasitic ciliate, Ichthyopthirius multifiliis (Ich) become immune to subsequent challenge, and produce serum antibodies that immobilize the parasite in vitro. Cell surface proteins targeted by these antibodies are referred to as immobilization antigens (i-antigens). Passive immunization of channel catfish with mouse monoclonal antibodies provides complete protection, suggesting that the i-antigens by themselves could elicit protective immunity. To test this hypothesis, vaccine trials were carried out using i-antigens that were purified to homogeneity by immunoaffinity chromatography, using an immobilizing mouse monoclonal antibody as ligand. Fifty channel catfish (10-15 g), were injected twice intraperitoneally ag a two week interval with 10 micrograms of purified protein in complete or incomplete Freund's adjuvant. Negative control fish were injected similarly with either BSA, or an irrelevant 14 kDa Ich protein. Positive control fish were injected ip with live Ich, 8000 to 10000 cells per fish at a five week interval, without adjuvant. All fish were challenged with 15,000 live Ich per fish at week 12 after the first injection. Results indicated that 72% of the fish injected with purified i-antigen, and 59.2% of fish injected with live organisms survived challenge. All negative control fish dies within 16 days after challenge. Furthermore, there was a significant difference (p<0.001, Kruskal-Wallis test ANOVA) in the median days to death among the control fish and the small percentage of fish that died following vaccination with i-antigen or live Ich. Fish injected with i-antigen or live Ich developed and maintained high immobilizing antibody levels in serum beginning two weeks from the first injection, while those injected with BSA or 14 kDa had no response. Antibody levels in mucus samples were only detectable at week 11 after the first injection. These results indicate that purified i-antigen elicits protective immunity and illustrate its potential use as a subunit vaccine against Ichthyopthirius multifiliis.   Return to 23rd Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page