Experimental induction of the carrier state in yearling brook trout: a model challenge protocol for IPNV immunization

Brook trout fry (Salvelinus fontinalis) were not protected from infectious pancreatic necrosis virus (IPNV) challenge by immersion vaccination with inactivated, purified virus at concentrations of 10(7) to 10(9) pfu/ml. Mortalities in vaccinated groups were higher than for the unvaccinated control group and appeared to be dose-dependent. A challenge protocol for adult brook trout was developed for future vaccine trials. A single intraperitoneal injection of virulent, purified virus was sufficient to make long-lasting carriers of 16 month-old trout. Fish underwent a transient viremia, identified by virus isolation from plasma and leucocytes. Feces were the most reliable samples for identification of IPNV carriers by non-sacrificial testing. Many fish in the remaining infected group were still carriers 12 and 27 weeks post-infection.