Coronaviruses: Structure, Naming, Multiplication, Implications, Control

ABSTRACT

The viral family of Coronaviridae has an important genus that affects humans called Coronavirus (CoV). CoVs distinct spike surface protein projections and its single stranded enveloped RNA give this virus its distinguishable structure. It is the spike surface proteins which bring about virus entry into host cells and the RNA to facilitate multiplication within the host. Once multiplication has begun this virus causes a range of respiratory illnesses; some methods of control based on the virus's physical structure and means of multiplication have used been utilised to treat the implications of the virus. This paper reviews current knowledge and any new findings about the structure, multiplication, effects and methods of control of coronaviruses.

INTRODUCTION

CoV affect a range of species and have been found able to ¨jump¨ from one species to another. First history of human coronaviruses emerged in the 1960’s after being found responsible for a significant amount of upper respiratory tract infections in children (Kahn, Jeffrey S., and Mcintosh 2005), they have been placed into sub-groupings of alpha, beta, gamma and delta (Centres for Disease Control and Prevention 2020). There are three CoVs which have emerged that have caused fatal illness in humans, SARS- CoV, 2002, MERS- CoV, 2012 and most recently in 2019 SARS-CoV-2 (Jonsdottir, Hulda R., and Dijkman 2016). CoVs like all other viruses are distinguished by their simplest organizational structure and means of multiplication. It is the means of this structure that dictates its implications on organisms as well as the methods by which it can be controlled (Funke, Tortora, and Case 2013).

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CORONAVIRUSES STRUCTURE

Viruses are microorganisms which contain a nucleic acid and a protein coat that surrounds the nucleic acid. They multiply inside living cells by using the cell’s ribosomes and can transfer their viral nucleic acid to other cells. (Funke, Tortora, and Case 2013) This is the basic structure and mechanism of all viruses. CoVs are viruses which consist of polyadenylated positive strand RNA enveloped within nucleocapsid protein, this is further encapsulated by an integral membrane glycoprotein. (Spaan, W., D. Cavanagh, and M. C. Horzinek 1988). CoVs also have very characteristic large spike glycoproteins jutting out of its surface giving it its identifiable ¨crown¨ shape under the microscope (Jonsdottir, Hulda R., and Dijkman 2016).

The polyadenylated positive strand RNA ranges in length from 26 to 32 kilobases (kb) being one of the largest genomes of RNA viruses (Schoeman, Dewald, and Burtram C. Fielding 2019). While being the virus´s genome it can also act as messenger RNA (mRNA) for the genome to be directly replicated within the host using the host's ribosomes. This is due to the polyadenylated ¨tails¨ providing the replicated molecules with stability preventing degradation (Libretexts, “9.8A: Positive-Strand RNA Viruses of Animals,” 2020).

The three structural proteins of CoVs each have their own function. The nucleocapsid protein is a multifunctional protein which assists in viral RNA transcription and assembly (Mcbride, Ruth, Van Zyl, and Fielding 2014). The integral membrane protein is involved in many actions of the virus´s lifecycle including assembly and pathogenesis (Schoeman, Dewald, and Burtram C. Fielding 2019). Finally, the spike surface proteins of the virus have also been found to be multifunctional proteins aiding in entry to host cells by binding and fusing to the host cells (Fang 2016).

HOW CORONA VIRUSES ARE NAMED

CoVs got its name stemming from the Latin word for crown, ¨corona¨ due its characteristic ¨crown¨ shape it has when observed under a microscope due to it spike surface glycoproteins (Jonsdottir, Hulda R., and Dijkman 2016). The virus genera can be further sub-grouped into Alphacoronavirus, Betacoronavirus, Deltacoronavirus and Gammacoronavirus each usually affecting a different group of species (McIntosh 2020).

To name each virus under these genera they are usually given the anagram for the syndrome it causes for the organism, for example, the CoV which causes Middle Eastern Respiratory Syndrome in camels, bat and even humans is named MERS- CoV. If there are two different CoVs causing similar syndromes they are distinguished by a number which represents the chronological order in which they were discovered, for example, the Severe Acute Respiratory Syndrome, SARS-CoV was found in 2002 and SARS-CoV 2 was found in 2019 (World Health Organization 2020).

MULTIPLICATION

All viruses when they have entered the host´s cells, rapidly multiply their viral genome within the host. The process of RNA replication is done by utilizing host ribosomes and a polymerase enzyme which helps bind the molecule together. The viral RNA has its own polymerase enzyme named non-structural protein 12 (nsp12) as well as two other proteins, non-structural proteins 7 and 8, which binds to the replicated RNA until it has been copied (Goodsell 2020)

CoV genome replication has been characterized by the formation of cytosolic double membrane vesicles within the host cells for the RNA replication. It was uncertain of how the replicated RNA was able to leave through the double membrane, but recent studies have found that there is a molecular pore that spans the double membrane allowing the replicated RNA to leave the vesicle and enter the host cell cytosol (Georg Wolff et al., 2020).

IMPLICATIONS

The degree of implications differs with each CoV as well as the host organism. In felines CoVs can result in lymphocyte depletion and macrophage infection, however, in chickens it can cause renal as well as respiratory diseases (Dandekar, Ajai A., and Stanley Perlman. 2005). CoV in humans have namely caused respiratory syndromes in those affected, it has been found that SARS-CoV and SARS-CoV 2 causes diffuse alveolar damage in the lungs due to pneumonia, affecting oxygen uptake and long-term breathing problems. Studies have also found that there are long-term implications affecting the heart from atrophy of heart muscles and can cause strokes and may increase risk of Parkinson´s and Alzheimer´s disease. However, there are still many unknown effects of SARS-CoV 2 on the human body due to its recent discovery (Gu, and Korteweg 2007) (Mayo Clinic 2020). Due to SARS-CoV 2 becoming a pandemic it not only has implications on the human body, but it also affects many other socio-economic factors of human life (Maria Nicola et al. 2020).

CONTROL METHOD

There has been no specific drug or therapeutic treatment yet determined for CoVs but there have been a range of control or treatment methods being utilized around the world. Some targeting control of spread of the virus between person to person and targeting control if infected by the virus namely, SARS-CoV 2. Control of spread has been done by implementing the wearing of facial masks, maintaining a six-foot distance between persons, sanitization of surfaces as well as regular hand washing. These are all done to prevent inhalation or encountering another person´s respiratory droplets from sneezes, coughs or even talking (Centers for Disease Control and Prevention 2020).

Medicinal methods being used to control the virus in those who do get infected are targeting the virus´s structure and means of multiplication. Some of the drugs given to patients infected function by inhibiting the virus binding and fusion to the host cells preventing virus entry and hence RNA replication within cells. Others function by means of preventing viral RNA replication affecting the nsp12 which is essential in CoV RNA replication (Chaplin 2020). However, while these may help control in some persons affected, they are still in undergoing investigations as to which treatment is best.

CONCLUSION

Coronaviruses are complex viruses which affect a range of organisms. They are composed of enveloped single stranded positive polyadenylated RNA surrounded by an integral membrane with spike surface proteins. Each coronavirus is named after the anagram for the syndrome in which causes in organisms, they are further distinguished by assigning a chronological number in which they were discovered. Coronaviruses multiply like all other viruses by utilization of the host´s ribosomes but they also utilize very specific enzymes and proteins to carry out their RNA replication. While they may require these conditions to replicate RNA, they are still able to exist in many different hosts causing a range of ailments and diseases in each species. It is also through these specific proteins and enzymes that provide the basis for many control methods in those infected, while to prevent the spread, there are methods of preventing contact of person to person respiratory droplets.

RECOMMENDATIONS

There are still many unknowns to coronaviruses especially in terms of control. There should first be effective methods developed to prevent spread from species to species as well as human to human spread by means of a protective vaccine. Further research development can be done to specifically target coronavirus spike surface proteins to completely prevent virus binding and fusion to host cells, hence preventing viral RNA replication within the host and diseases it brings with it.

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