It was once thought that the host range of Hepatitis B Virus was limited to humans, its natural host, and a few other higher primates such as chimpanzees.
Then this theory could be regarded as history because a related virus was isolated from Beechey ground squirrels (Otospermophilus beecheyi), that were living near Palo Alto in northern California (USA). The virus shares many antigenic, molecular and biological features with Hepatitis B Virus of humans, indicating that they are members of the same virus group. It was given the name of Ground Squirrel Hepatitis B Virus.
These days we know better because Ground Squirrel Hepatitis B Virus has also been isolated from the Richardson ground squirrel (Spermophilus richardsonii) that is living in Canada. It suggests that Ground Squirrel Hepatitis B Virus is geographically more widespread than previously considered.
 Barker et al: Viral hepatitis, type B, in experimental animals in American Journal of Medical Sciences - 1975
 Marion et al: Ground squirrel hepatitis virus infection in Hepatology - 1983
 Minuk et al: Ground squirrel hepatitis virus (GSHV) infection and hepatocellular carcinoma in the Canadian Richardson ground squirrel (Spermophilus richardsonii) in Liver - 1988