Liver disease associated with duck hepatitis B virus infection of domestic ducks

The liver disease associated with duck hepatitis B viremia was investigated in naturally infected ducks from Chi-tung county in China and in both naturally and experimentally infected ducks from the United States. Liver and serum specimens of adult Chinese ducks were examined for duck hepatitis B virus (DHBV) DNA by dot and gel blot hybridization. DHBV was found in serum and (in episomal form only) in livers of 6 of 11 birds exhibiting various degrees of chronic hepatitis. In 1 bird with hepatocellular carcinoma, DHBV DNA was detected at the limit of assay sensitivity and in another not at all, contrasting with findings in humans and woodchucks. In work with California Pekin and Khaki Campbell ducks, known amounts of DHBV were injected into the egg 10 days before, or into ducklings 1 day after, hatching and the livers were examined 6 weeks later. The majority of the injected ducklings had viremia detectable by hybridization 1 or 2 weeks after injection. The presence but not the amount of viremia correlated with incidence and degree of hepatitis, determined under code. The most severe instances of hepatitis, all in Pekin ducks, resembled the hepatitis in adult Chinese ducks of Chi-tung county. Severe and moderate hepatitis were found only in indoor-caged injected animals with viremia and in some uninjected birds without viremia that had been kept in outdoor flocks. The latter hepatitis, as some hepatitis in adult Chinese ducks, may not be related to DHBV. Mild and insignificant hepatitis were also found in injected and noninjected ducklings, some of which had the vertically transmitted spontaneous viremia previously described. The good correlation of experimentally induced viremia with incidence and severity of hepatitis in the Pekin duckling provides a simple, rapid, and relatively inexpensive model to study the relation of lesions to hepatitis B family infection in nonprimates.