Georgia
Veterinary Scholar
Program

Ichthyophthiriasis: Protective mechanisms of immune catfish.

Aquaculture is a rapidly growing enterprise with promise for future prominence in the food industry. Infection of freshwater fishes by the ciliated protozoan parasite Ichthyopthirius multifilis is one economic barrier to achieving such prominence; a better understanding of the mechanism of immunity will aid in vaccine development and allow this barrier to be overcome. Our current model of immunity involves a behavioral change in the parasite whereby it exits the fish upon exposure to protective antibodies. To further examine this model we monitored the progress of infection and immune response in immune and naïve channel catfish, Ictalurus punctatus, after challenge with infective theronts. We measured immobilizing antibody titers and utilized immunohistochemical staining against the immobilizing membrane antigen of the parasite as well as against catfish immunoglobulin, western blotting, and H&E histological examination of collected tissues. Serum immobilizing-antibody titers of immune fish ranged from 1280-20480; parasites and parasite antigen were found in the gills of immune fish six hours after the challenge, but were not present in samples taken 24 hours or later post-challenge. No parasites were found in the skin of immune fish with these titers and parasite antigen was only found in skin samples taken at six hours post-challenge; skin samples of immune fish taken at six hours post-challenge also had approximately twice the number of mucus-producing cells of naïve fish (11.43 cells per HPF versus 5.77 cells per HPF, respectively). Naïve fish had significantly higher parasite counts than immune fish and, histologically, gill sections showed significantly more parasites than skin sections. Based on the rich blood supply to the gills, the high sera titres of the immune fish, and the lack of parasites or antigen in samples taken 24 hours or later from immune fish, these findings support our model of immunity.

Georgia Veterinary Scholar


Jon Anderson
Univ of Georgia
Class of 2003

Faculty Mentor

Joanne Maki,
Dept. Medical Microbiology