A Review on COVID19: Evolution, Structure of Corona Virus and Comparison of COVID19 with Common FLU

Covid-19 is a pandemic disease that threatened the World both socially and economically. The virus originated from Wuhan – China in December 2019. Globally 18,354,342 cases were reported and total mortality cases are 6,96,147 till Aug 5 2020. The spreading of Novel Covid19 is faster than MARS and SARS Virus. The symptoms are very similar to the common cold or flu such as running nose sneezing, sore throat are the common symptoms and difficulty in breathing, severe muscle ache, dry cough GIT irregularity were the serious symptoms. The infection may leads to pneumonia, Acute Respiratory disorder (ARD) Syndrome. The incubation period varies from 714 days. The transmission occurs through physical contact with infected person, infected droplets and contaminated objects. Laboratory test includes CT scan, Nasal Oral pharyngeal swab tests, RT PCR were employed for diagnosis. The disease at the end of August showed increasing mortality rate. Maintaining Physical distance is the only measure to overcome the infection.


Introduction
The Entire World is suffering from pandemic disease Covid19. Covid19 is caused by a group of viruses called Corona. The corona virus belongs to a large family of Coronaviridae and order 'Nido' virus. The name 'Corona' derived from Latin word 'Coronum' which means crown-like appearance on its external surface called spikes. The human corona virus was first seen in the year 1965 which was known to cause the common cold in humans. After several years the similar human and animal viruses were identified and named as corona virus for its crown-like appearance.  Transmission: The first Covid case was identified in Hunan seafood market of Wuhan China. It was pre assumed that the infection was from bat to humans but the study revealed that there was no transmission of virus from bat to human.
Spreading mechanism: Primarily the transmission of virus occurs through Respiratory droplets of infected persons from coughing or sneezing. It can also be transmitted through direct or close contact with infected person secretions like saliva, nasal droplets and respiratory droplets. Transmission may also occur through fomites in the immediate environment around the infected person. Airborne transmission can also occur in health workers during medical procedures that generate (1).
Receptor recognition: The entry of Corona viruses into the host cell is mediated by Spike proteins. The Corona spike consists of 3 segments namely ectodomain, transmembrane anchor and intracellular tail. The ectodomain has receptor binding S1 subunit and membrane fusion S1 contains C Terminal Domain(S1-CTD), N terminal Domain(S1-NTD) The Spike C Terminal Domain(CTD`s) recognises the ACE2 (Anginotensin Converting Enzyme) of the hostepithelial cells. The S1 CTD`s, S NTD`s are grouped into RBD (Receptor binding Domain). (5).

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International Journal of Arts, Science and Humanities Replication of viral particles: According to Anthony R. Fehr and Stanley Perlman, the Viral RNA synthesis follows the translation and assembly of the viral replicase complexes. Viral RNA synthesises and produces both genomic and sub-genomic RNAs. Sub-genomic RNAs serve as mRNAs for the structural and accessory genes which reside downstream of the replicase polyproteins. All positive-sense sub-genomic RNAs are 3′ co-terminal with the full-length viral genome and thus form a set of nested RNAs, a distinctive property of the order Nidovirales. Both genomic and sub-genomic RNAs are produced through negative-strand intermediates. (6) After replication the Spike, Envelope and Membrane translated and continues to assembling. After assembling the viral particles -virons get transported to cell surface by exocytosis. .

International Journal of Arts, Science and Humanities
The Covid-19 and Influenza exhibits similar symptoms both causes respiratory illness. But the Covid 19 shows mild from asymptomatic and leads to serious illness and can be fatal. The difference between these infections is how they spread. Diagnosis: The Swab test, naso-oropharyngeal samples, Serological test are preliminary tests. The etiological diagnosis of Covid19 is RT-PCR (Reverse Transcriptase Polymerase Chain Reaction) Assay and also an Antigen-Antibody based test also conducted. (11) Incubation Period: The medical incubation period for Covid19 is about 5 to 11 days similar to SARS. (7) Treatment: Till now there are no vaccines and antiviral drugs available for treating covid19. The treatment is symptomatic and oxygen treatment against respiratory impairment, Non Invasive (NIV) and invasive Mechanical Ventilation (MIV) for Oxygen therapy (2). Antiviral drugs like Lopinavir/Ritonavir, anti-flu drugs such as Oseltamivir, Favipiravir, Immumo-modulatory drugs like Chloroquine, Hydroxychloroquine, Serotheraphy (Obtained antibodies from healed individual), Anticoagulant (to prevent venous thromboembolism), corticosteroids [treat pneumonia and Acute Respiratory Distress Syndrome(ARDS)].(8) Hence administering the antibiotics for common cold and flu mimics the symptoms of Covid19. The stress/ anxiety causes the Chest pain which results in rapid heartbeat may induce the Shortness of breath which is a most serious symptom of Covid19. (1) Psychological support increases the immunity. According to Jennifer N. Morey et al.,(9) the individuals exposed to chronic can exhibit immune dysregulation.

Prevention
General awareness is the main factor to overcome the infection. Using masks and sanitizers, maintaining the social distance, avoiding the risky behaviour like visiting to covid hotspots or containment zones that increase the risk of infections. Most of the infection is reporting in Health care workers, to overcome these personal protective equipments like N95 masks, goggles and protective units should be provided. Care should be taken while drawing the swab sample for testing. Patients should be isolated for at least a week or till the appearance of negative results. At community level people should avoid crowds, gathering should be prohibited. Maintenance of hygiene, travelling should be avoided. Psychological and moral support with the patients affects the immune system.

Conclusion
Covid19 is a pandemic disease declared by WHO. It is a deadly respiratory illness that emerged from SARS CoV2. The infection is more common with the persons who were immunologically weak. The majority of cases were between the ages of 25-64 years. The mortality rates are increasing day by day. The virus outbreak challenges the World Economy. The Environmental pollution has been decreased due to Lockdown instance. Increasing the mental health of the patients decreases immunity dysregulation. It is better to maintain physical distance than the social distance.