**2. Virology of SARS-CoV-2**

Coronaviruses (CoVs) belongs to the family *Coronaviridae* and the order *Nidovirales* possessing a single-stranded, positive-sense RNA genome ranging from 26 to 32 kb in length [4]. SARS-CoV and SARS-CoV-2 comes under the genus *Betacoronavirus* of the subfamily *Orthocoronavirinae* and is further belongs to subgenus *Sarbecovirus* [5].

Based on the phylogenetic tree analysis, nucleotides of SARS-CoV-2 shares 96% sequence identity with the SARS-like (SL) virus named BatCoV-RaTG13/Bat-SL-RaTG13 [6] and 88–88.2% identity [6–8] with bat-derived SARS-like coronaviruses named Bat-SL-CoV-ZC45 and Bat-SL-CoV-ZXC21, suggesting that bats are the most likely reservoir. Interestingly, the phylogenetic study showed that MERS-CoV and SARS-CoV were about 50% and 79% similar to SARS-CoV-2, respectively [6, 7]. The Spike (S) protein of SARS-CoV-2 was found to be approximately 75% homologous to the SARS-CoV spike [6].

The organization of the CoV genome contains a 5′-leader-UTR-replicase-S(Spike)- E (Envelope)- M(Membrane)- N(Nucleocapsid)-3′ UTR-poly(A) tail with accessory genes interspersed in the structural genes on the 3′ end of the genome [9]. In 5′ terminal, 2/3rd of viral RNA primarily locates the first ORF (ORF1a/b) which translates 2 polyproteins namely, pp1a and pp1ab, and encodes 16 non-structural proteins (NSP), while the remaining ORFs encode accessory and structural proteins [10]. The structural proteins of SARS-CoV-2 contains spike (S), an envelope (E), membrane (M) and nucleocapsid (N) protein that are located at the one third 3′ terminal of the genome [11]. The critical step for SARS-CoV-2 entry is binding of trimeric spike (S) glycoprotein to host cell angiotensinconverting enzyme 2 (ACE2) receptors similar to that of SARS-CoV entry [6]. Coronavirus nAbs targets primarily surface spike glycoprotein that mediate viral entry into host cells. The symptoms of COVID-19 most commonly are fever, cough, myalgia or fatigue, dyspnoea, pneumonia and lesser common were sputum production, headache and diarrhea. The complication of SARS-CoV-2 are mostly acute respiratory distress syndrome (ARDS), followed by shock, myocardial dysfunction and acute kidney injury [12, 13]. A detailed overview of COVID-19 disease progression was discussed, with particular reference to immunopathology and immunobiology [14].

SARS and MERS are caused by zoonotic coronaviruses that belong to the genus *Betacoronavirus* within *Coronaviridae.* SARS-CoV emerged in southern China in 2003 and caused 8098 cases worldwide, including 774 related deaths with an estimated 14–15% case-fatality rate [15]. In 2012, the first case of MERS occurred in Saudi Arabia. A sum of 2,494 cases and 858 related deaths with an overall case-fatality rate up to 34.4% [16]. More than 10 million confirmed cases of SARS-CoV-2 were reported globally by WHO, including 503,867 associated deaths as on the date of compilation 30th June-2020 (**Figures 1** and **2**). A total of 566,840 confirmed cases of SARS-CoV-2 were reported in India, including 16,893 associated deaths as on the date of compilation 30th June-2020 (https://covid19.who.int/) (**Figures 3** and **4**).

*Convalescent Plasma Immunotherapy - A Possible Mitigation Strategy for SARS-CoV-2 Pandemic DOI: http://dx.doi.org/10.5772/intechopen.98254*

#### **Figure 1.**

*Total number of cumulative SARS-CoV-2 cases and deaths across the globe during current pandemic. Source adapted from (https://covid19.who.int/). [accessed 2020-06-30].*

#### **Figure 2.**

*Total number of daily new confirmed SARS-CoV-2 cases and deaths across the globe during current pandemic. Source adapted from (https://covid19.who.int/). [accessed 2020-06-30].*

#### **Figure 3.**

*Total number of daily new confirmed SARS-CoV-2 cases and deaths in India during current pandemic. Source adapted from (https://covid19.who.int/). [accessed 2020-06-30].*

**Figure 4.**

*Total number of SARS-CoV-2 cumulative cases and deaths in India during current pandemic. Source adapted from (https://covid19.who.int/). [accessed 2020-06-30].*
