The IPNV carrier state and demonstration of vertical transmission in experimentally infected brook trout

Intraperitoneal injection of virulent infectious pancreatic necrosis virus (IPNV) into yearling brook trout Salvelinus fontinalis induced an asynlptomatic, chronic w u s infection that persisted for at least 76 wk post-lnlection (wpl) in spite of the production of a strong humoral immune response. At 8 wpi, 100 % of the fish in one of the injected groups were IPNV camers , as determined by organ and feces samphng. At 76 wpi. 95 % of the fish remained IPNV carriers. Vertical transmission of IPNV to progeny occurred, but the fry mortality rate, the prevalence of IPNV-infechon, and mean IPNV titres were low. Hence, vertical transm~ssion 1s not recommended as a criterion for evaluating the efficacy of broodstock immunization. The IPNV carner state in yearlings that had survived a &rect mmersion in IPNV as fry was equivalent to that induced in yearlings by injection, in terms of the number of IPNV-infected organs per fish and the prevalence and titre of IPNV in the visceral organs when fish were sampled at 73 and 76 wpi, respectively. However, the Injected yearlings mounted a stronger humoral immune response to IPNV that the fish surviving the direct unmersion. Smce the IPNV camer state induced by injechon was nearly indistinguishable from the natural IPNV carner state, intraperitoneal injechon can be used as a challenge protocol for broodstock immunization tnals.