Table 2. Virus detection by cell culture and RT-PCR at persistent period (6 months).

Strains	1 month		2 months		3 months		4 months			5 months		6 months
	CC	RT-PCR	CC	RT-PCR	CC	RT-PCR		CC	RT-PCR	CC	RT-PCR	CC	RT-PCR
TA	5/5	Nd	3/5	2/2	0/5	4/5		2/5	3/3	2/5	3/3	5/5	Nd
TT	5/5	Nd	4/5	0/1	0/5	5/5		2/5	3/3	1/5	4/4	5/5	Nd

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.