Infectious pancreatic necrosis virus: transmission from infectious to susceptible rainbow trout fry

Fry of rainbow trout Oncorhynchus mykiss were exposed to serotype VR-299 of infectious pancreatic necrosis virus (IPNV) by using a standardized immersion challenge. In concurrent experiments, fish were monitored for 11 d for excretion of IPNV or monitored for 9 d for excretion and transmission of IPNV to susceptible rainbow trout fry. Immersion-challenged fish began excreting virus within 2 d after challenge. The rate of IPNV excretion per fish increased steadily from about day 4 to day 8 and then decreased. Virus concentrations in tissues of immersion-challenged fish increased exponentially. Susceptible fish became infected with IPNV within 4 d after being introduced to immersion-challenged fish (e.g., 2 d after the challenged fish began excreting virus). By 9 d, 84% of the susceptible fish were infected with IPNV.