RESUMEN
Experimental inoculation of naive ducks with duck hepatitis B virus (DHBV) can lead to one of three outcomes, namely, persistent viremia, transient infection with or without viremia, or no evidence of infection. The ability of individual ducks to resolve DHBV infection was found to be linked to the age of the duck at the time of inoculation and the dose of inoculated virus. (1) In recently hatched ducks inoculated intravenously (i.v.) with 4 x 10(4) DHBV DNA genomes, a switch from persistent viremia to transient antibody appearance was seen at an age of inoculation between 7 and 14 days. A 25-fold increase in the dose of virus (1 x 10(6) DHBV genomes) delayed this switch by 7 days. (2) When 4-month-old ducks were inoculated i.v. with different doses of virus, only those receiving the highest dose (2 x 10(11) DHBV genomes) showed viremia and extensive viral replication and histological changes in the liver; 2/3 ducks in this group had a transient infection, while the third duck had viral replication and histological changes in the liver that were still present at day 120 postinoculation (p.i.). In all ducks receiving lower doses (1 x 10(3), 1 x 10(6), 1 x 10(9) DHBV genomes) antibodies to viral surface and core antigens developed without detectable viral replication in the liver on days 6, 9, or 12 p.i. (3) When 10- to 16-month-old ducks were inoculated i.v. with 2 x 10(11) DHBV genomes, all showed extensive viral replication in hepatocytes and mild to moderate histological changes in the liver on days 4 or 6 p.i. In 4/5 ducks viremia was not detected, anti-surface antibodies were first detected on day 8 p.i., and viral DNA and antigen were cleared from the liver by days 35-47 p.i. The remaining duck became viremic with persistence of virus in the liver until at least day 46 p.i. The findings of the study are consistent with a model for noncytopathic viruses (R. M. Zinkernagel (1996) Science 271, 173-178).