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Several viral diseases that have been documented throughout history have become pandemic or infectious diseases. In the current situation, novel coronavirus disease 2019 (COVID-19) is also a viral infectious disease, and that is associated with many other health issues, including cancer, neurodegenerative diseases, and diabetes (Vehik et al., 2011; Sohrabi et al., 2017). To manage and prevent this disease, clinicians, scientists, national healthcare systems of different countries, and members of the World Health Organization (WHO) are continually searching for tools to solve this problem and fight against this disease (Sohrabi et al., 2017).
COVID-19 is a highly contagious viral disease and has now caused a pandemic since it was discovered in 2019. The first confirmed case of COVID-19 was identified in Wuhan, Hubei Province (China), in December 2019 with a respiratory problem. In India, the first COVID-19 case was registered in Kerala when the patient arrived from Wuhan, China. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Its symptoms include coughing/sneezing, fever, difficulty in breathing, chest pain, sore throat, gastrointestinal problems, and loss of sense of smell and taste, and it can also lead to brain and kidney dysfunction (Sohrabi et al., 2017). COVID-19 is a helical single-stranded, positive-sense RNA, and its genome size is 29.891 kb, enclosed by a 5¢-cap and 3¢-poly (A) tail. Its genome contains 38% G + C. COVID-19 has four main structural glycoproteins in its nucleocapsid: spike (S), membrane (M), envelope (E), and nucleocapsid (N) (Vehik et al., 2011; Sohrabi et al., 2017).
COVID-19 is spread mainly by droplets of an infected person through coughing or sneezing and this can happen in two ways: direct close contact and indirect contact to an infected person (Sohrabi et al., 2017). According to a WHO study, COVID-19 patients may be asymptomatic or symptomatic and associated with other symptoms such as “strange symptoms” or singing-skin rashes and “COVID tongue” or mouth ulcer or white patches on the tongue. These new symptoms are related to previous symptoms. Due to the rapid increase of COVID-19 cases (Boukhatem et al., 2020; Roosa et al., 2020), the WHO declared COVID-19 as a pandemic on January 30, 2020. Besides China, COVID-19 has affected all countries worldwide within a brief period; therefore, it has become a human health crisis of international concern (Vehik et al., 2011; Sohrabi et al., 2017).