# SARS-CoV-2 Detection Using Optical Fiber Based Sensor Method
## 2 Emergence and Features of COVID-19  
Coronaviruses are a diverse group of viruses that causes severe respiratory illnesses. In 2012, two types of zoonotic coronoavirl high pathogens, SARS and MERS viruses, created a deadly respiratory sickness in humans and formed a new public health hazard in the twenty-first century. The public health community has been concerned about the evolution of coronaviruses [15; 16; 17; 18]. Several health institutions in Wuhan, Hubei Province, China, observed clusters of individuals with pneumonia in late December 2019 [19]. Alpha coronavirus, Beta coronavirus, Gamma coronavirus and Delta coronavirus are the four genera of coronaviruses [18]. Recently, in November 2021, a new variant named the B.1.1.529 variant, commonly known as the Omicron variant, was reported in South Africa. Barely a month has elapsed since scientists in Botswana and South Africa alerted the world to a fast-spreading SARS-CoV-2 variant now known as Omicron. Researchers worldwide are racing to understand the threat that the variant--now confirmed in more than 20 countries--poses to the world. Yet it might take scientists weeks to paint a more complete picture of Omicron, and to gain an understanding of its transmissibility and severity, as well as its potential to evade vaccines and cause reinfections. Although genome sequencing is needed to confirm Omicron cases, some PCR tests can pick up a hallmark of the variant that distinguishes it from Delta variant. The emergence of Omicron has presented new challenges in the fight against SARS-CoV-2. A large number of mutations in the Spike protein suggest that its susceptibility to immune protection elicited by the existing COVID-19 infection and vaccines may be altered. Coronavirus is an enveloped, RNA virus. Microscopically, prominent club-shaped spikes appear from its surface which form a halo (Corona) around the virus. Once inside the human respiratory tract, these spikes enable the virus to enter the cells for replication. The transmission of coronavirus mainly occurs via respiratory aerosols. The virus is acquired either by inhalation of the aerosols or direct contact with the eyes, nose or mouth. The incubation period for COVID-19, which is the time between exposure to the virus (becoming infected) and symptom onset, is on average 2-10 days; however, it can be up to 14 days. During this period, also known as the \"presymptomatic\" period, some infected persons can be contagious. Therefore, transmission from a pre-symptomatic case can occur before symptom onset. Virus adsorbs onto the cell membrane via surface spikes. The Angiotensin Converting Enzyme-2 acts as a receptor for the virus in the lower respiratory tract. The virus typically limits itself to the mucosal cells of the respiratory tract. The virus then enters the cell after losing its envelope and replicates in the cell cytoplasm. After replicating, the virus acquires its envelope from the endoplasmic reticulum of the cell. Once the replication is complete, the virus exits the cell and effects other cells. The angiotensinconverting enzyme-2 is a crucial component of the renin-angiotensin-aldosterone system of the body, which is responsible for the regulation of the volume of bodily fluids. Binding of Coronavirus to the ACE-2 dysregulated the body fluid balance which causes diffuse edema of the respiratory tract, resulting in hypoxia. Involvement of the upper respiratory tract is characterized by Coryza (rhinorrhea), scratchy throat and low-grade fever. Involvement of the lower respiratory tract results in pneumonia, clinically manifesting as severe respiratory distress, fever, nonproductive cough, dyspnea and hypoxia. A spike (S), a membrane (M), an envelope (E), and a nucleocapsid (N) are the four different components of the virus (N). Among all reported RNA viruses, it possesses the biggest genome (26.4-31.7 kb). Single-stranded RNA is also found in the virus' genetic material [20; 21; 22].