Coronaviruses are enveloped, helical nucleocapsid viruses with a size of approximately 120 nm, containing single-stranded, positive-sense RNA (mRNA). They have the largest known RNA genome (approximately 30 kilobases) among all viruses. Coronaviruses cause infection in many different animals including but not limited to, pigs, cats, rodents, bats, as well as humans. Human coronaviruses (abbreviated as HCoV) belong to the Coronavirinae subfamily.

Human coronaviruses were first detected in patients with the common cold in the 1960s. Coronaviruses are transmitted through the respiratory tract and primarily affect the upper respiratory and gastrointestinal tract of mammals and birds. So far, 7 strains of coronavirus have been shown to affect humans (229E, NL63, OC43, HKU1, SARS-CoV, MERS-CoV, and SARS-CoV-2).

Until recently, the most known human coronavirus (SARS-CoV) caused the SARS (severe acute respiratory syndrome) epidemic, which was seen in South Asian countries between 2002-2004. On the other hand, SARS-CoV-2 was first detected in Wuhan, China at the end of 2019, and then quickly spread to different countries. It was defined as a pandemic, that is, a global epidemic, by World Health Organization (WHO) on March 11, 2020. The illness was initially referred to as the Coronavirus Disease 2019 (COVID-19), and it has now emerged as the coronavirus with the greatest level of public awareness.


Following the detection of the disease in December 2019, firstly Iran, followed by Italy, England, Brazil, and the USA, became the epicenter of the COVID-19 disease and reported the highest number of cases globally. With the effect of the delta variant, in April 2021, the worst figures in the epidemic were announced in India, with the number of daily 400 thousand cases and 5 thousand deaths. Simultaneously, the number of people who lost their lives in the epidemic in Brazil was reported between 2,000 and 4,000 for a long time.

Due to the Omicron variant, which was detected in November 2021 and thought to be much more contagious than the first studies, there has been a noticeable increase in cases both in Turkey and globally. Globally, as of 17 May 2023, there have been 766 million confirmed cases of COVID-19, including almost 7 million deaths, reported to WHO.

Signs & Sypmtoms

Similar in profile to common coronaviruses, SARS-CoV-2 primarily affects the upper and lower respiratory tract. SARS-CoV-2 infections are commonly counted as fever, dry cough, and malaise. In advanced pandemic processes, different symptoms such as muscle pain, sore throat, diarrhea, conjunctivitis, and loss of taste and smell have been detected with new variants. In severe cases, respiratory distress, shortness of breath, and chest pain are frequently observed. Health authorities recommend seeking medical attention if such symptoms are detected. Untreated cases often lead to death due to respiratory failure.


Although in the first period of the epidemic, the virus was associated with the transmission of the virus from animal to human, the later period was an important indication that human-to-human transmission is possible. According to the studies, and information from national and international health authorities, the transmission of Novel SARS-CoV-2 is agreed on that human-to-human by coughing and sneezing, through droplets, and by contact with contaminated surfaces. Likewise other respiratory infections, the rate of transmission is thought to be higher when the infection is symptomatic. In conclusion, it has been found that the most effective techniques for preventing infection are maintaining social distancing, wearing masks as much as possible, following personal hygiene guidelines, and vaccination.


Although different methods such as CT and rapid tests are used in the diagnosis of the disease, Real-Time PCR kits stand out as the most advantageous and widely used diagnostic kits in terms of result precision and time to result.


The virus causing the disease was named Novel Coronavirus at first and abbreviated as 2019-nCoV. After taxonomic studies, it was revealed that the virus has a similar genetic structure to SARS-CoV, which is the cause of SARS, and accordingly, its nomenclature was updated to SARS-CoV-2 by WHO.

Although it is known that the SARS-CoV-2 virus is of bat origin, research on the transmission process to humans is still ongoing. Many mutations have been identified in SARS-CoV-2. This is because of its single-stranded RNA genetic material, which allows relatively high mutation rates. These mutations can be found in many gene regions and result in a variety of outcomes, some of which may or may not have any significance. In this process, different variants emerged, primarily Alpha, Beta, Gamma, and Delta, which were categorized by the coexistence of different mutation groups. Experts in South Africa discovered the Omicron version in November 2021. It is far more contagious than earlier variations and is anticipated to have a lower lethality and hospitalization rate. Although studies are still ongoing, preliminary results suggest that this variant is approximately 4 times more contagious than the Delta variant.

According to studies, the mutations in the gene region that encodes the S protein are important, as that protein is responsible for the attachment of the virus to the host cell. Even though vaccinations used to fight the virus are made in accordance with this protein, there is still a big issue since virus mutations diminish the efficiency of these vaccines. As a result, the virus can significantly increase the rate of transmission, bodily harm, and mortality. There has been a decrease in mortality rates with the increase in global vaccination rates, but the global risk continues due to situations such as countries with no/restricted access to vaccines, individuals with chronic diseases or at risk, and the fact that vaccines provide a lower protection against newly released variants than expected.

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