**6. History of COVID-19**

It was on record that animal respiratory infections linked to the coronavirus group had occurred precisely in chickens earlier in the 1920's, with a mortality rate of 40–90% [25]. The virus, identified as infectious bronchitis virus, was then cultivated in 1937 as Beaudette strain. Two other viruses of the coronavirus group responsible for murine encephalitis and mouse hepatitis virus were detected in the later part of 1940 [26]. However, scientists did not realize that these three viruses had similarities [26, 27]. In the course of research activities on common cold, a group of Scientists namely David Tyrrell, C. Kendall and Malcolm Bynoe, and David Tyrrell in 1961



*Occupational Stress-Related Sleep Anomaly in Frontline COVID-19 Health Workers… DOI: http://dx.doi.org/10.5772/intechopen.109148*

isolated a distinct virus and was designated as B814 [28, 29]. Unfortunately, the virus could not be cultivated using the same methods which were used for adenoviruses, rhinoviruses, and many more. It was not until 1965 that the new virus was grown courtesy of a technique that involves serial passage through human embryonic trachea organ culture [30]. It was observed that inoculation of the novel virus into volunteers through the intranasal route resulted in cold. However, inactivation of the virus occurs in the presence of ether showing the virus exhibits lipid envelope. Thereafter, the isolate was grown in kidney tissue culture and designated as 229E [31]. 229E was capable of being inactivated just like B814 by ether [32]. In 1967, Scientists were able to compare 229E, B814, and infectious bronchitis virus and with the aid of an electron microscope, they were found to be related [26]. Specifically, they were observed to exhibit a crown-like presentation [33]. Therefore, the word 'corona' is a Greek meaning 'crown or wreath' in English and was formulated to describe the signatory appearance of a group of viruses [34]. OC43 was another novel respiratory virus with similar morphology as infectious bronchitis virus, 229E, and EB814. Exclusive investigations on these strains dated over 20 years after the discovery and it was shown that while the latter demonstrated a tendency of orchestrating epidemic in the entire United States, the former was more associated with local outbreak. It was later clear that apart from these strains, other respiratory viruses exist.

Over the years, many other strains have been discovered. For instance, in 2003, a human coronavirus named severe acute respiratory syndrome-coronavirus (SARCOV-1) was identified. This virus infects pulmonary epithelial cells [35] in bats, palm civets and humans [36, 37] using angiotensin-converting enzyme 2 (ACE2) [38]. Human Coronavirus NL63, another positive sense single-stranded enveloped RNA which invades the host cell through ACE2 was also detected in 2013. Human coronavirus HKU1 was detected in 2004 in Hongkong using N-acetyl-9-Oacetylneuraminic acid receptor [39]. In 2013, Middle East coronavirus (MERS-COV) was discovered [10]. This virus was found to infect bats, humans, and camels by binding to Dipeptidyl peptidase 4 (DPP4) receptors. In 2019, severe acute respiratory syndrome-coronavirus-2 was discovered in Wuhan, China [40].

Coronaviruses are responsible for 15% of common cold [41]. Other features signifying coronavirus infection are swollen adenoids, pneumonia, sore throat, bronchitis, fever, and many more [42]. Human coronavirus OC43, human coronavirus HKU1, human coronavirus 229E, and human coronavirus NL63 produce mild symptoms while Middle East respiratory syndrome-coronavirus, severe acute respiratory syndrome-1 coronavirus, and severe acute respiratory syndrome-2 coronavirus produce potentially severe problems [11].
