Fig. 3

The SARS-CoV-2 replication and pathogenesis. a The SARS-CoV-2 infects upper and lower respiratory tract. b The virus replication from 1 to 12 has been described as, (1) The virus identifies the ACE-2 receptor. (2) The binding is initiated by the Spike (S) glycoprotein of SARS-CoV-2 by receptor binding domain (RBD) to the ACE-2 receptor binding motif (RBM). (3, 4) The virus-receptor internalization occurs and a membrane fusion is carried out by S2 subunit of S glycoprotein followed by the uncoating of +ssRNA inside cytoplasm. (5–7) The +ssRNA directly translate into non-structural proteins for initiating the viral replication through RNA-dependent RNA polymerase (RdRp/nsp12) and forms -ssRNA which act as template for synthesizing various copies of +ssRNA. (8–10) The +ssRNA along with the structural protein are trafficked to ER-Golgi complex for assembly and maturation. (11–12) The vesicles-encapsulated virion fuses with the cell membrane and through exocytosis release outside the cell to infect nearby cell. The immune response: the cellular RNA receptors like, RIG-I and MDA-5 recognized the dsRNAs in cytoplasm, activating the pro-inflammatory response and antiviral response inside cells. The cytokines activate the macrophages and lymphocytes to kick start both cellular and humoral response. c The virus disseminates to the other part of body through blood affecting the brain, heart, liver spleen, large intestine, kidneys