Susceptibility of Arctic char to experimental challenge with infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV)

Arctic char Salvelinus alpinus were exposed to the fish pathogens infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) to estimate susceptibility of the species to infection. Fish were immersion challenged at 46, 74, and 95 d posthatch for 5 h in viral concentration of 10(3) or 10(5) PFU(plaque-forming units)/mL and were monitored for 21 d postchallenge. Fish that died were assayed individually for virus-associated mortality, and survivors were assayed individually to estimate prevalence of virus carrier status. Arctic char succumbed to IHNV infection with population losses as high as 41%, and prevalence of IHNV carriers in surviving fish was 24% or less with virus titers in carrier fish ranging from 2.5 x 10(2) PFU/g to greater than 1.3 x 10(6) PFU/g. Infections with IPNV resulted in losses of 20% or less, and prevalence of IPNV carriers in surviving fish was as high as 82% with virus titers in carrier fish ranging from 2.5 x 10(2) PFU/g to greater than 5.0 x 10(6) PFU/g Logistic regression models were developed for the mortality and infection data for each virus. For IHNV, the odds of dying or becoming infected were significantly greater for the fish from the 74-d age-group than for the fish from the 46-d or 95-d age-groups. Fish exposed to 10(5) PFU of IHNV/mL had significantly greater odds of dying or becoming infected than fish exposed to 10(3) PFU/mL. For IPNV, the odds of dying were significantly greater for the 74-d age-group compared with the other tyro age-groups. The 74-d fish were also significantly more likely to become infected than the 95-d-old fish. Fish exposed to 10(5) PFU of IPNV/mL had significantly greater odds of dying or becoming infected than fish exposed to 10(3) PFU of IPNV/mL.