Coronaviruses: An Updated Overview of Their Replication and Pathogenesis

Abstract

Coronaviruses (CoVs), enveloped positive-sense RNA viruses, are characterized by club-like spikes that project from their surface, an unusually large RNA genome, and a unique replication strategy. CoVs cause a variety of diseases in mammals and birds ranging from enteritis in cows and pigs, and upper respiratory tract and kidney disease in chickens to lethal human respiratory infections. Most recently, the novel coronavirus, SARS-CoV-2, which was first identified in Wuhan, China in December 2019, is the cause of a catastrophic pandemic, COVID-19, with more than 8 million infections diagnosed worldwide by mid-June 2020. Here we provide a brief introduction to CoVs discussing their replication, pathogenicity, and current prevention and treatment strategies. We will also discuss the outbreaks of the highly pathogenic Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV), which are relevant for understanding COVID-19.

Keywords: Coronavirus; MERS-CoV; Nidovirales; Positive-sense RNA viruses; SARS-CoV.

Figure 1.. Genome Organization of Representative α, β, γ and δ-CoVs.

An illustration of the MHV genome is shown on top. The replicase gene constitutes two ORFs, rep 1a and rep 1b, which are expressed by a ribosomal frameshifting mechanism. The expanded regions below show the structural and accessory proteins in the 3′ regions of α-CoVs (HCoV-229E), β-CoVs (MHV, SARS-CoV, and MERS-CoV), γ-CoVs (IBV) and δ-CoVs (PDCoV). The total genome size is given for each virus. The sizes and positions of accessory genes are indicated, relative to the basic genes S, E, M, and N. The size of the genome and individual genes are approximated using the legend at the top of the diagram but are not drawn to scale.