Virus detection by cell culture and RT-PCR at persistent period (6 months).

Result of reisolation by cell culture (CC) or detection of virus genome by reverse transcriptase PCR (RT-PCR). Numbers indicate positive/examined for the two methods. When all fish in one group were positive by cell culture they were not examined by RT-PCR. When fish were negative for cell culture, they were subsequently examined by RT-PCR. Strains indicate IPNV strains used for challenge and time points are time post challenge. Nd-not done.