CHARACTERIZATION OF AGE-RELATED AND DOSE-RELATED OUTCOMES OF DUCK HEPATITIS-B VIRUS-INFECTION

Experimental inoculation of naive ducks with duck hepatitis B virus (D HBV) can lead to one of three outcomes, namely, persistent viremia, tr ansient 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 in travenously (i.v.) with 4 x 10(4) DHBV DNA genomes, a switch from pers istent 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 v irus (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 t he liver; 2/3 ducks in this group had a transient infection, while the third duck had viral replication and histological changes in the live r that were still present at day 120 postinoculation (p.i.). in all du cks receiving lower doses (1 x 10(3), 1 x 10(6), 1 x 10(9) DHBV genome s) antibodies to Viral surface and core antigens developed without det ectable viral replication in the liver on days 6, 9, or 12 p.i. (3) Wh en 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 mi ld to moderate histological changes in the liver on days 4 or 6 p.i. I n 4/5 ducks viremia was not detected, anti-surface antibodies were fir st 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 p ersistence of virus in the liver until at least day 46 p.i. The findin gs of the study are consistent with a model for noncytopathic viruses (R. M. Zinkernagel (1996) Science 271, 173-178). (C) 1998 Academic Pre ss.