Diversity of CoV pathogenesis
Different CoVs display diverse host range and tissue tropism. Usually, alphacoronaviruses andbetacoronaviruses infect mammals. In contrast, gammacoronaviruses and deltacoronaviruses infect birds and fish, but some of them can also infect mammals. Before 2019, there were only six CoVs that were known to infect human and cause respiratory diseases. HCoV-229E, HCoV-OC43, HCoV-NL63, and HKU1 cause only mild upper respiratory disease, and in rare cases some of them can cause severe infection in infants, young children and elders. SARS-CoV and MERS-CoV can infect lower respiratory tract and cause severe respiratory syndrome in human.