28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Differences In Virulence Between Two Serotypic Strains Of Ichthyophthirius multifiliis Alton G. Swennes, Jane G. Noe, and Harry W. Dickerson Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602 Two serotypic strains of the parasitic ciliate Ichthyophthirius multifiliis were shown to infect with differing levels of virulence in naïve channel catfish (Ictalurus punctatus).  These strains, NY1 and G5, of serotypes A and D respectively, display different surface immobilization antigens.  The comparative virulence of the two strains was analyzed using quantitative tail fin infections.  Parasite numbers on the fishes’ tails at various time points were measured.  The numbers of days-to-death of infected fish also was determined.  It was found that I. multifiliis strain NY1 was more virulent than the G5 strain due to its higher replication rate and its subsequent ability to confer greater mortalities among infected fish.  Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page