Immunization against furunculosis in rainbow trout with iron-regulated outer membrane protein vaccines: Relative efficacy of immersion, oral, and injection delivery

Rainbow trout Oncorhynchus mykiss were protected (relative percent survival > 80%) after use of a formalin-killed whole-cell furunculosis vaccine, grown in iron-depleted conditions, administered by intraperitoneal (i.p.) injection followed by an oral boost. This combination resulted in higher levels of protection than vaccination solely by i.p. injection, immersion, or oral administration. By means of an enzyme-linked immunosorbent assay, antibody was not detected in the skin and gut mucus or bile of fish after any vaccination regimen. Yet humoral antibodies were produced against the outer membrane proteins (maximum titer = 1:2,560 at day 105) and iron-regulated outer membrane proteins (IROMP; maximum titer = 1:12,800 on day 105) of Aeromonas salmonicida after vaccination by the i.p. route with an oral boost. However, we were unable to correlate circulating antibodies against IROMP antigens with protection from injected laboratory challenge.