**Abstract**

At the end of December 2019, in Wuhan, China, a rapidly spreading unknown virus was reported to have caused coronavirus disease of 2019 (COVID-19). Origin linked to Wuhan's wholesale food market where live animals are sold. This disease is caused by SARS Coronavirus-2 (SARS-CoV-2), which is closely related to the Severe Acute Respiratory Coronavirus (SARS-CoV) and the Middle East Respiratory Syndrome Coronavirus (MERS-CoV). This virus shares a high sequence identity with bat-derived SARS-like Coronavirus, which indicating its zoonotic origin. The virus spread globally, provoking widespread attention and panic. This Coronavirus is highly pathogenic and causes mild to severe respiratory disorders. Later, it was declared a global pandemic by the World Health Organization (WHO) due to its highly infectious nature and worldwide mortality rate. This virus is a single-stranded, positive-sense RNA genome, and its genome length about 26 to 32 kb that infects a broad range of vertebrates. The researchers worldwide focus on establishing treatment strategies on drug and vaccine development to prevent this COVID-19 pandemic. A drug repurposing approach has been used to identify a rapid treatment for the people affected by COVID-19, which could be cost-effective and bypass some Food and Drug Association (FDA) regulations to move quickly in phase-3 trials. However, there is no promising therapeutic option available yet. This book chapter addresses current information about the COVID-19 disease, including its origins, impacts, and the novel potential drug candidates that can help treat the COVID-19.

**Keywords:** COVID-19, Zoonotic virus, SARS-CoV-2, Epidemiology, Drug discovery, Therapeutics

#### **1. Introduction**

Nowadays, there is growing concern and perceived threat due to the outbreak of the novel coronavirus disease, COVID-19, as named by the World Health Organization (WHO), which poses a peril of pandemic to the global public health. The epicenter of the novel Coronavirus was located in Wuhan province of China, where the outbreak originated in December 2019 due to Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) [1]. This disease has spread to 220 countries, with over 158 million confirmed coronavirus cases of 3.3 million confirmed

deaths with 136 million recoveries worldwide as of May 10, 2021 [2]. Also, millions of people's lives have been affected as mandatory isolations/quarantines instructed. The adverse effect of the COVID-19 outbreak could bring significant challenges to the health system globally and could have far-reaching consequences on the global economy if the virus's spread is not effectively curtailed [3, 4].

Coronaviruses (CoVs) are encapsulated within a membrane envelope containing a single-stranded positive-sense RNA genome. Spikes of glycoprotein that give coronaviruses their crown-like appearance are studded with the viral membrane. Coronaviruses infect humans as well as animals such as bats that host the widest range of coronaviruses [5]. There are four types of alpha, beta, gamma, and deltadesignated coronaviruses. Extreme acute respiratory syndrome virus (SARS-CoV), Middle East respiratory syndrome (MERS-CoV), and SARS-CoV-2 are included in the beta coronavirus class [6, 7]. SARS-CoV-2 targets the lower respiratory system to induce viral pneumonia, similar to SARS-CoV and MERS-CoV, but may also affect the heart, kidney, liver, and central nervous system, resulting in multiple organ failure [8]. New evidence suggests that SARS-CoV-2 is more contagious/ transmissible than SARS-CoV and MERS-CoV [9]. Glycosylated spike (S) protein acts as a significant inducer of host immune responses, which mediates both SARS-CoV and SARS-CoV-2 host cell invasion by binding with angiotensin-converting enzyme 2 (ACE2) located on the host cells of the surface membrane [1].

With the onset of the second wave of COVID-19 infection, developing countries like India seem to be reeling in the most catastrophic damages. Since late March of 2021, the emergence of COVID-19 infected patience has skyrocketed to more than 22 million people and have touched a record number of 4000 death per day in the first week of May 2021. The outbreak has left the country struggling hard to cope with the healthcare needs of patients. This silent killer disease creates havoc on earth, yet the upcoming course of this virus is unpredictable. Therefore, necessary measures are needed to control and eradicate this alarming problem to save the people's precious life and the country's economy [4, 10]. However, significant steps have been taken by the government of different countries. Many countries such as Italy, Germany, and India have "lockdown" the whole country to break the chain by quarantine and confinement of people to the homes. To date, there is no clinically approved antiviral drug or vaccine available to be used against COVID-19; therefore, it has posed a public health emergency and a global threat to the entire world. Repurposing existing medications is an affordable and effective therapeutic technique. The scientific community reacted quickly with a suggested list of current drugs with therapeutic potential for COVID-19, based on genomic sequence knowledge. This chapter examines the source of infection, the SARS-CoV-2 transmission pathway, and the medications currently being clinically tested for COVID-19 management to include references for follow-up research, prevention, and treatment that may help readers gain the latest understanding of this emerging infectious disease.

### **2. History**

The first case of Coronavirus infection was detected in 1960. Twice in the past two decades, history has seen incidences where β-coronavirus has cross over from animal to humans in severe infectious diseases. Till 2003, coronavirus infection was considered to be a non-fatal disease. However, with many mortally affecting cases of severe acute respiratory syndrome cropping up in Hong Kong, the United States of America, Vietnam, Taiwan, and Thailand culminated in the deciphering of the deadly pathogenesis of this disease and led to the declaration of disease as a state emergency by World health organization (WHO) in 2004 [10–13]. In 2012, almost a decade later,

the Middle East respiratory syndrome coronavirus, also known as MERS-CoV, arose in Saudi Arabia, killing 858 and affecting 2494 people. This virus also originated from bats, and dromedary camels were possibly its intermediate host [14].
