A brief molecular insight of COVID-19: epidemiology, clinical manifestation, molecular mechanism, cellular tropism and immuno-pathogenesis

Abstract

In December 2019, the emergence and expansion of novel and infectious respiratory virus SARS-CoV-2 originated from Wuhan, China caused an unprecedented threat to the public health and became a global pandemic. SARS-CoV-2 is an enveloped, positive sense and single stranded RNA virus belonging to genera betacoronavirus, of Coronaviridae family. The viral genome sequencing studies revealed 75-80% similarity with SARS-CoV. SARS-CoV-2 mainly affects the lower respiratory system and may progress to pneumonia and Acute Respiratory Distress Syndrome (ARDS). Apart from life-threatening situations and burden on the global healthcare system, the COVID-19 pandemic has imposed several challenges on the worldwide economics and livelihood. The novel pathogen is highly virulent, rapidly mutating and has a tendency to cross the species boundaries such as from bats to humans through the evolution and natural selection from intermediate host. In this review we tried to summarize the overall picture of SARS-CoV-2 including origin/ emergence, epidemiology, pathogenesis, genome organization, comparative analysis with other CoVs, infection and replication mechanism along with cellular tropism and immunopathogenesis which will provide a brief panoramic view about the virus and disease.

Keywords: COVID-19; Infection; Pandemic; Pathogenesis; SARS-CoV-2.

Fig. 1

Countries, territories or areas with reported confirmed cases of COVID-19, 30 March 2021 ( Source: www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports)

Fig. 2

Epidemiological comparison of respiratory viral infections

Fig. 3

Genome organization of SARS-CoV-2

Fig. 4

SARS-CoV-2 Spike protein conformation, entry, fusion and replication. 1 SARS-CoV-2 interacts with host's ACE2 receptors and transmembrane protease serine 2 protein (TMPRSS2) through the spike protein. 2 It is followed by two entry pathways either A. non-endosomal or B. endocytic pathway or both to enter the host cell. 3. Soon after its entry into host cell, it releases its genome and overtake protein synthesis machinery of host cell and start the translation of RdRp 4 Afterward SARS-CoV-2 replication and transcription are catalyzed by RdRp

Fig. 5

Overview of immunological aspect of COVID-19 indicating the viral induced immune modulation in the infected host tissues. SARS-CoV-2 is recognised by the pattern recognising receptors by the T cells which in turn initiates a cascade of events particularly cytokine storm, recruitment of inflammatory cells etc., ultimately resulting in multiple organ damage and the development of symptoms that are associated with the progression of COVID-19 disease