Immunosuppression in rainbow trout, Salmo gairdneri Richardson, caused by the haemoflagellate Cryptobia salmositica Katz, 1951

Publisher Website
Google Scholar
Abstract
An experimental Cryptobia salmositica infection in rainbow trout, Salmo gairdneri Richardson, produced suppression of the humoral response against sheep red blood cells as measured by direct haemagglutination. Two‐month and 5‐month infections produced equal suppression. The parasite also produced suppression of the humoral response against a bacterial pathogen, Yersinia ruckeri. Anti‐Y. ritckeri titres were significantly lower in most fish infected with C. salmositica than in non‐infected fish. Immunosuppression became evident when C. salmositica first appeared in the blood (first 2 weeks of infection), Immunosuppression was confirmed by challenge with Y. ruckeri. Mortality at challenge occurred in 64·3% to 83·3% of the fish already infected with C. salmositica at the time of initial Y. ruckeri exposure. There was no mortality at challenge if fish were not infected with C. salmositica at initial bacterial exposure, nor in those concurrently infected with both pathogens. Antigenic competition may have caused the immunosuppression.