Hepatocellular carcinoma in Richardson's ground squirrels (Spermophilus richardsonii): evidence for association with hepatitis B-like virus infection.

During studies of seasonal obesity, a high frequency of hepatic neoplasms was observed in Richardson's ground squirrels. Of 12 Richardson's ground squirrels examined thoroughly, 7 had mild or moderate degrees of chronic portal hepatitis and 6 (50%) had hepatocellular carcinoma. Serological tests for hepadnavirus surface antigen, anti-core antibody and virion DNA that recognize the ground squirrel hepatitis virus of California ground squirrels (Spermophilus beecheyi) were uniformly negative. Southern blot analyses of EcoRI digests of liver cell DNA demonstrated 3.2 kb fragments that hybridized with a ground squirrel hepatitis virus-specific probe in nontumorous liver tissue from 6 of 10 ground squirrels and in hepatocellular carcinoma specimens from 2 of 5 squirrels indicating infection with a hepadnavirus related to ground squirrel hepatitis virus. Failure, however, to detect serum antibody to ground squirrel hepatitis core antigen suggested probable antigenic differences between the ground squirrel hepatitis virus of California ground squirrels and the putative Richardson's ground squirrel agent. Further studies are required to fully characterize the hepadnavirus of Richardson's ground squirrels and to determine its relationship to hepatocarcinogenesis in this species.