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.