**Abstract**

Novel coronavirus (SARS-CoV-2) out-broke in the city of Wuhan in China and widely spread across the globe in a pandemic manner, causing societal and economic disruptions. Though the origin of the novel virus is still a debating topic, it is certain that SARS-CoV-2 acquired human to human transmission capacity. Regardless of aggressive containment and quarantine approaches, the number of confirmed cases continues to rise and being reported due to its highly infectious nature. As of the time, there is a little scope for the antiviral drugs or vaccines for the treatment of coronavirus infection; due to the vigorous mutation rate in the viral genome. However, existing anti-parasite drugs like ivermectin and chloroquine could effectively inhibit the virus has been reported. Few of the vaccines have come up with certain degree of efficacy and many are under the clinical trial phase. The research on novel coronavirus is still in the preliminary stage. In this chapter, we systematically summarize the origin, transmission route, molecular characterization, pathogenic mechanism, contagious nature, clinical symptoms, diagnosis, treatment, mutation and infection as well as prevention strategy of coronavirus disease based on the recently available literature. In addition to this, this chapter presents updated insights of the current state of knowledge pertaining to novel coronavirus and can be referred for potential future studies.

**Keywords:** Novel coronavirus (SARS-CoV-2), coronavirus disease, prevention strategy, transmission capacity, drug targets, treatment methods, virus structure, mutation

### **1. Introduction**

In December 2019, Wuhan city in China became the center of origin of the novel coronavirus disease with the acronym COVID-19 outbreak that continues to spread quickly across the globe in a very short time. Due to its severe infection rate, on January 30, 2020, World Health Organization (WHO) declared COVID-19 as the public health emergency of international concern (PHEIC), followed by a worldwide pandemic declaration on March 11, 2020. As of May 5, 2020, it has spread to 220 countries with 3665403 confirmed covid-19 positive cases. The recent data (as of June 28, 2021) show that the number of countries affected by Covid-19 is 229, with a total of 181,741,361 confirmed cases of COVID-19 and 3,936,510 deaths. It is anticipated that the full extent of spreading and severity of this 2019 novel coronavirus is yet to be seen and global control of COVID-19 will be one of the toughest challenges humanity has ever faced [1, 2]. According to the international committee on taxonomy of viruses (ICTV) classifications,

coronaviruses belong to the order *Nidovirales*, family *Coronaviridae*, and sub-family *Coronavirinae,* as shown in **Figure 1**. These are the largest group of viruses belonging to the *Nidovirales* order. The sub-family *Coronavirinae* is further divided into four genera, such as *Alphacoronavirus*, *Betacoronavirus*, *Gammacoronavirus*, and *Deltacoronavirus*withfour different lineages (A (*embecovirus*), B (*sarbecovirus*), C (*merbecovirus*), and D (*nobecovirus*)) of the *Betacoronavirus*genus [3, 4]. COVID-19, officially named by the WHO on February 11, 2020, is caused by the severe acute respiratory syndrome coronavirus 2 (named by ICTV), otherwise known as SARS-CoV-2. The emerging SARS-CoV-2 is a beta coronavirus of lineage B and seems to be the seventh member of the coronaviruses that infect humans, primarily targeting the respiratory system [5]. The first human coronavirus (HCoV), named B814, was isolated in 1965 from patients with common cold [6]. The other six different HCoVs include severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), HCoV- 229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1. Among these HCoVs, HCoV-NL63 and HCoV-229E belong to *Alphacoronavirus*, HCoV-HKU1 and HCoV-OC43 belong to lineage A, SARS-CoV to lineage B, and MERS-CoV to lineage C of the *Betacoronavirus*as depicted in **Figure 1**.

HCoVs are zoonotic pathogens that originated in animals and all HCoVs are believed to have a bat origin, with the exception of *Betacoronavirus* lineage A that

**Figure 1.** *Classification of novel corona virus.*

#### *COVID-19: An Updated Insight of the Pandemic DOI: http://dx.doi.org/10.5772/intechopen.99097*

may have rodent origin [7, 8]. Similar to the case of other SARS-CoVs, the bat might be the probable origin for SARS-CoV-2 as SARS-CoV-2 shares about 96% wholegenome sequence similarity with the bat coronavirus (BatCoV). The confirmed and suspected origins of HCoVs are summarized in **Figure 2**.

Zhou et al. (2020), through complete genome analysis of samples collected from COVID-19 patients, found that SARS-CoV-2 is a *Betacoronavirus* with a sequence identity of 96% with a bat coronavirus [9]. Studies of Pasteur Institute, Shanghai also highlighted that the natural hosts of SARS-CoV-2 might be the bats [10]. However, few studies also highlighted that the pangolin is expected as an intermediate host of the SARS-CoV-2 [11, 12]. Zhang et al. (2019) reported that coronavirus from the pangolin might be the origin of the SARS-CoV-2 on the basis of genome sequence identity [11]*.* However, the claim was rejected by Cyranoski (2020), based on the fact that the origin is not by the genomic sequence similarity but by the receptor-binding domain (RBD) of the virus that enables the virus to enter the host cell [13]. Although, the potential natural and intermediate host of the virus is not fully established, regardless of its initial transmission source, it is certain that SARS-CoV-2 acquired the capacity for human to human transmission [14]. SARS-CoV-2 is highly infectious; the entire population is generally highly susceptible to infection, and respiratory droplets through coughing and sneezing of COVID-19 patients and coming into contact with them are the primary infectious source in the population. It is even claimed by some experts that transmission during conversations through micro-droplet may possibly be the third infection route. The digestive tract can also be a potential route of infection as SARS-CoV-2 is detected in the stool and gastro-intestinal tract of COVID-19 patients, in addition to its detection in saliva, tear, urine, etc. [15, 16]. There was no evidence of transmission from mother to child during pregnancy [17]. Though based on the currently available evidence, bats are considered to be the natural hosts and pangolins are the intermediate hosts, the origin of SARS-CoV-2 necessitates further in-depth investigations.

**Figure 2.** *Probable origin and intermediate host during interspecies transmission of the corona virus.*
