Protection of channel catfish Ictalurus punctatus following natural exposure to Edwardsiella ictaluri and effects of feeding antigen on antibody titer

Abstract

Channel catfish Ictalurus punctatus that survived a natural infection of Edwardsiella ictaluri demonstrated a strong relationship between E. ictaluri agglutination antibody titer and degree of protection upon challenge. Intraperitoneal injection of 2.0 x 10(7) cells fish-1 killed 100 % of fish with antibody titers of 0 and 128 (low); 77.8 % of fish with titers from 256 to 512 (medium); and 57.7 % of the fish with titers of > 1024 (high). A second challenge trial, using 5.1 X 10(5) cells fish-1, produced 72.2 % mortality in fish with no detectable antibody titers, 51.3 % in low antibody titer fish, 25.0 % in medium antibody titer fish, and 6.5 % in high antibody titer fish. These results demonstrate that channel catfish have protective antibodies after they are exposed to E ictaluri but that a titer of over 256 is necessary to ensure detectable protection against an injected challenge. If fish are challenged with large numbers of pathogen this protective immunity can be overcome. Administration of E. ictaluri cell extract impregnated feed every 5 or 10 d to fish vaccinated by injection resulted in the fish maintaining their antibody titer, whereas the antibody titers of fish receiving no oral vaccine continued to decline. PU - INTER-RESEARCH PI - OLDENDORF LUHE PA - NORDBUNTE 23, D-21385 OLDENDORF LUHE, GERMANY