Contemporary human viruses most likely originated by cross-species transmission from non-human animals. Examples include HIV-1, which crossed from chimpanzees to humans, and SARS coronavirus, which originated in bats. Since the 1989 discovery of hepatitis C virus (classified as a hepacivirus in the family Flaviviridae) the origin of the virus been obscure. During the characterization of respiratory infections of domestic dogs, a virus was discovered that is the most genetically similar animal virus homolog of HCV.