Hepatitis B virus (HBV, illustrated) is a substantial human pathogen. WHO estimates that there are now 240,000,000 individuals chronically infected with HBV worldwide, of which 25% will die from chronic liver disease or hepatocellular carcinoma. The hepatitis B virus vaccine is highly effective at preventing infection. Because there are no known animal reservoirs of the virus, it is believed that HBV could be globally eradicated. The recent finding of HBV in bats raises the possibility of zoonotic introduction of the virus.