Early events in duck hepatitis B virus infection. Sequential appearance of viral deoxyribonucleic acid in the liver, pancreas, kidney, and spleen.

Early events in duck hepatitis B virus infection were studied in 1-day-old ducklings following inoculation. Group A ducklings (n = 26) were inoculated intraperitoneally with 10 microliter of infective serum, and group B ducklings (n = 29) were inoculated with 50 microliter. Samples of the serum, liver, pancreas, kidney, and spleen were taken, starting 3 h after inoculation and continuing through the 14th day. In group A, relaxed circular double-stranded deoxyribonucleic acid (DNA) did not appear in serum until day 10, whereas single-stranded DNA, indicative of active replication of the virus, was already demonstrable in the liver on day 6. In group B, single-stranded DNA was first detected in the liver on day 3, and relaxed circular double-stranded DNA became detectable in the liver and serum on day 6. The pancreas started to have single-stranded DNA on day 10 in group A and on day 6 in group B, suggesting active viral replication in this organ soon after it occurred in the liver. In the spleen, relaxed circular double-stranded DNA was detectable when serum became positive for viral DNA, probably due to contamination by serum DNA. However, single-stranded DNA became detectable on day 14 in group A and on day 6 in group B, suggesting a delayed but active viral replication in the constituent tissues of the spleen. These results have demonstrated that active replication of duck hepatitis B virus starts in the liver after infection, and is followed by the pancreas, the kidney, and the spleen. The incubation period is shortened when larger amounts of virus are inoculated, but the sequential occurrence of viral replication in these organs remains the same.