Coronaviruses are viruses that circulate among animals. Some coronaviruses can infect humans. Many human coronaviruses come from bats which are considered natural hosts of these viruses. The virus is then thought to be passed on through an intermediate host to humans. The first SARS-CoV originated in bats and was transmitted to humans via civet cats, while MERS-CoV emerged in humans through the intermediate host of camels. The precise way in which SARS-CoV-2 was transmitted from animals to humans is currently unknown.