2.3  Transmission routes of the disease
2019-nCoV is thought to be transmitted through droplets, close contact, aerosol and maybe fecal-oral transmission, and patients in the incubation period can transmit the virus to other persons [5]. The distribution of the viral receptor can explain the pathogenic mechanisms, clinical manifestations and transmission routes of 2019-nCoV [20,21]. ACE2, a receptor for 2019-nCoV, is necessary for the viral entry of 2019-nCoV. The ubiquitous expression of ACE2 in various cells, such as lung AT2 cells, esophagus upper, stratified epithelial cells, and absorptive enterocytes of ileum and colon may contribute to the multi-tissue infection of 2019-nCoV [22]. Therefore, besides respiratory and bodily contact, fecal-oral transmission is a potential route for 2019-nCoV infection [23,24].