The coronavirus disease 2019 (COVID-19) which has become the pandemic par excellence of our time places pressure on various aspects of human endeavor and as such requires detailed study to better combat it. However, diagnostic tests were used to provide data on the incidence of COVID-19 and to assess the immune status of infected individuals. The objective of this chapter is to describe the diagnostic methods currently used to identify SARS-CoV-2 infection. Obtaining the first SARS-CoV-2 genome sequence was decisive for the development of molecular diagnostic assays that currently make it possible to diagnose and screen for the Sars-CoV-2 infection. Their uses depend on the target to be detected. Antigenic tests detect the presence of a virus antigen, which usually makes a proteinaceous part of the virus surface. The serology tests detect the presence of antibodies generated against SARS-CoV-2 and are also a relevant tool for epidemiological studies.
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In December 2019, a major outbreak of Wuhan, atypical pneumonia of unknown an etiology, was reported to the World Health Organization (WHO) country office of China.The CDC's (Chinese Center for Disease Control and Prevention) country office in China has identified its etiology as a new virus belonging to the family coronaviruses (CoV) and initially received the provisional designation of the 2019 new coronavirus (2019-nCoV), which includes the alpha and gamma coronaviruses. SARS-CoV-2 is a betacoronavirus (β-CoV) that is structurally similar to other coronaviruses (SARS-CoV and MERS-CoV) from the Coronaviridae family (Zhu et al., 2020). Other authors have classified coronavirus into four genera, based on genetic features, namely Alphacoronavirus, Betacoronavirus, Deltacoronavirus and Gammacoronavirus (Mavrodiev et al., 2020;Shors, 2021). This new coronavirus infects and replicates in the lung parenchyma pneumocytes and macrophages in which the ACE-2 cell receptor resides (Reina, 2020). This new virus was called SARS-CoV-2 and the disease it produces was called COVID-19 highly infectious, whose rapid global spread has put the entire world in a state of emergency, leading humans to an unprecedented global pandemic situation. On 1stJanuary 2021, there have been 81, 947, 503 confirmed cases of COVID-19, including 1, 808, 041 deaths, reported to WHO (WHO, 2021). On January 30th, 2020 the WHO declared a Public Health Emergency of International Concern (WHO, 2020a). According to data released by the WHO the country’s most affected by COVID-19 are the United States of America, India, Brazil, Russian Federation, France, United Kingdom, Italy, Spain, Germany, Colombia, Argentina and Mexico their incidence has been reported by their government agencies respectively at 19,578,217; 10,305,788; 7,675,973; 3,212,637; 2,129,376; 1,893,502 (WHO, 2020a).
The virus that affects us now is very similar to those that caused the epidemics (more limited, fortunately) that we call SARS in 2003 and MERS in 2012(Del Rio et al., 2020). All three are descended from bat viruses, which evolved to acquire the ability to cause disease in humans. In fact, it is so similar to SARS that it is considered a “relative” of “SARS-CoV-2”. Their helical nucleocapsid surrounds a non-segmented genome (27–32 kb) characterized by a 5ʹ-end containing gene important for viral replication and pathogenesis in the host cell (Monchatre-Leroy et al., 2017; Cui et al., 2019; Saif et al., 2019).The 3ʹ-end genomic region harbours genes for nucleocapsid and membrane proteins (Yoshimoto et al., 2020).
This virus has a zoonotic origin and has been transmitted to humans via an unknown intermediate host, leading to infections in humans and other mammals (Lam et al., 2020). Susceptible animals could serve as reservoirs of the virus, requiring rigorous and ongoing animal management and surveillance. The infected person may not show symptoms and remain asymptomatic, and some may show severe symptoms in their respiratory and digestive organs (Monchatre-Leroy et al., 2017; Cui et al.,2019).