Chapter 1 - Introduction

Abstract

Coronaviruses infect humans and multiple animal species. The seven coronaviruses of humans are the following: HCoV-NL63, HCoV-229E, HCoV-OC43, HCoV-KHU1, SARS-CoV, MERS-CoV, and SARS-CoV-2. The former four coronaviruses usually cause mild upper respiratory disease, such as the common cold, but can also cause croup and other more serious diseases, especially in the elderly and people with comorbidities. The latter three coronaviruses cause lower respiratory tract diseases which can be severe to life-threatening. The genome of coronaviruses is positive-sense single-stranded RNA composed of 4–5 structural proteins and up to 16 nonstructural proteins. The spike protein binds to several different host target cell receptors, depending on the virus. This protein directs the host species and cell types that may be infected by each coronavirus. Coronaviruses are divided into four genera: Alpha-, Beta-, Gamma-, and Delta-voronavirus. All known human coronaviruses are alpha- and beta-coronaviruses, while gamma- and delta-coronaviruses are primarily found in birds. Human and other mammalian coronaviruses are believed to have originated in bats and rodents and entered the human population via zoonotic transmission from intermediate hosts. SARS-CoV and SARS-CoV-2 are believed to have used civet cats, raccoon dogs, and, perhaps, pangolins from live animal markets “wet markets” in China as their intermediate hosts while dromedary camels in Saudi Arabia are the intermediate host for MERS-CoV., This chapter briefly reviews basic information about the history of infectious agents in humans, an introduction to viruses and other microbes, and basic characteristics of the immune system, including vaccines, in addition to an introduction of the shared features of coronaviruses and treatment regimens.