CORONAVIRUS

Image Source - Google | Image by - coronavirusexplained.ukri.org

Introduction:-

       Coronaviruses belong to the subfamily Coronavirinae in the family Coronaviridae of the order Nidovirales and can cause respiratory, digestive, and nervous system diseases in humans and many other animals. Coronavirus (SARS-CoV-2) is a single-stranded RNA-enveloped virus. Coronavirus particles are spherical with a diameter of approximately 80 to 160 mm. The envelope surface is covered with spike (S) protein, and the membrane (M) proteins and envelope (E) proteins are located among the S proteins. 

       

                The genomic RNA and phosphorylated nucleocapsid (N) protein forms a spiral nucleocapsid, which is located within the envelope. An RNA-based metagenomic next-generation sequencing approach has been applied to characterize its entire genome, which is 29,881 bp in length, encoding 9860 amino acids, constituting the longest known genome among RNA viruses.

             This genome has a 5′ cap structure, a 3′ polyadenylate tail structure, and six open reading frames (ORFs), of which the first (ORF1) near the 5′ terminus encodes 16 nonstructural proteins (nsp1–16) involved in viral replication and transcription. The S, E, M, P and N genes encode structural proteins whereas, nonstructural proteins, such as 3-chymotrypsin like protease, papain-like protease, and RNA-dependent RNA polymerase, are encoded by the ORF region.

                                            

                                                      

                                        

Image Source - Google | Image by - medicalxpress.com

                                       

                        According to genetic and antigenic characteristics, coronaviruses can be divided into four genera: α, β, γ, and δ. Among them, α and β coronaviruses only infect mammals, while γ and δ mainly infect birds, although some can also infect mammals. Except for SARS-CoV and the Middle East Respiratory Syndrome Coronavirus (MERS-CoV), most coronaviruses do not cause severe diseases in humans. 
       

         It has been confirmed that the recent outbreak and epidemic of coronavirus disease 2019 (COVID-19) was caused by a new coronavirus that has been named SARS-CoV-2. Different from SARS-CoV and MERS-CoV in genetics and epidemiology, SARS-CoV-2 is a novel β coronavirus. As of now, three types of highly pathogenic coronaviruses have been confirmed, namely SARS-CoV, MERS-CoV, and SARS-CoV-2.

History:-

                     The World Health Organization (WHO) had declared the coronavirus disease 2019 or (COVID-19) as a pandemic a year and a half ago. The COVID-19 pandemic continues to be an ongoing global pandemic caused by severe acute respiratory syndrome coronavirus 2 or (SARS-CoV-2). A pandemic is defined as occurring over a large geographic region and affecting an exceptionally high proportion of the population. The last pandemic reported in the world was H1N1 flu pandemic in the year 2009.

         The virus was first recognized on 31st December 2019 in Wuhan, China. There were few cases of pneumonia of unidentified etiology admitted to the hospital. It was quickly recognized and accepted that this was neither SARS (Severe Acute Respiratory Syndrome) nor MERS (Middle-East Respiratory Syndrome) or any other common respiratory pathogens. They had the attributes of a coronavirus infection and were quickly shown to result from a hitherto un-recognized coronavirus which was initially named 2019- nCoV (2019-novel Coronavirus), but has now been renamed as SARS-Coronavirus 2 (SARS CoV-2) because it also causes severe acute respiratory syndrome.

      

          By January 11th, 2020, there were 41 cases of this sickness in Wuhan; most were benign, but seven were significant infections, and there had been one demise by that period. The disease was spread by human-to-human transmission. It was highly contagious and soon it found outside the Wuhan, in surrounding Hubei Province, and elsewhere in China. The first case of COVID-19 outside China was in Thailand, and the patient was a 61 years old woman who had come from Wuhan. Due to severe restrictions on movement in Wuhan and the surrounding Hubei province, the Chinese government was able to get the epidemic under control at that time, but COVID-19 had been spreading worldwide since then.

 

The World Health Organization declared a Public Health Emergency of International Concern regarding COVID-19 on 30th January 2020.  Then it had declared as a pandemic on 11th March 2020.

Image Source - Google | Image by- sciencedirect.com

After the end of the first wave of SARS CoV-2 infections or COVID-19 (April 2020), China had reported 81,865 cases, 3,335 deaths and 77,370 patients were recovered. Overall, the case of fatality rate in Wuhan was 0.9-2.1%.

By the end of the second week of April 2020, there had been 1.5 million cases of COVID-19 in the whole world with 91,000 deaths and 3,42,000 people had recovered from this infectious disease.

 

Image Source - Google | Image by - wikimedia.org

As of 30th May 2021, more than 169 million cases were confirmed. More than 3.53 million deaths are confirmed in COVID-19 and making it one of the deadliest pandemics in history.

Classification:-

        The name of Coronavirus comes from the Latin word "Corona" meaning "crown", because when viewed under an electron microscope, they look like spiky crown-like structures. In this classification the Order Nidovirales, Coronaviruses are the most important in human disease. Coronavirus belongs to the subfamily Orthocoronavirinae, which is one of two subfamilies in the family Coronaviridae, order Nidovirales, and realm Riboviria.

Image Source : Google | Image by - wikipedia.org

They are divided into four genera:-

i) α-coronaviruses,

ii) β-coronaviruses,

iii) γ-coronaviruses,

iv) δ-coronaviruses.

 

[Note:- α-Coronaviruses and β-Coronaviruses infect mammals, while γ-Coronaviruses and δ-Coronaviruses primarily infect Aves (Birds).]

 

Genus: α-coronavirus (α-coronaviruses usually cause mild upper respiratory tract infections in humans and it includes HCoV-NL63 and HCoV-229E. A member of  this class of coronaviruses is  Porcine epidemic diarrhea virus)

 

Species:- α-coronavirus 1

•TGEV

•Feline coronavirus

•Canine coronavirus

•Human coronavirus 229E

•Human coronavirus NL63

•Miniopterus bat coronavirus 1

•Miniopterus bat coronavirus HKU8

•Porcine epidemic diarrhea virus

•Rhinolophus bat coronavirus HKU2

•Scotophilus bat coronavirus 512

 

Genus: β-coronavirus [Beta coronaviruses which causes COVID-19 disease, includes MERS CoV, SARS CoV-1 and SARS CoV-2 and HCoV-OC43 and HCoV-HKU1;which usually cause less severe respiratory symptoms]

 

Species:- β-coronavirus 1

•Bovine Coronavirus

•Human coronavirus OC43)

•Hedgehog coronavirus 1

•Human coronavirus HKU1

•Middle East respiratory syndrome related coronavirus

•Murine coronavirus

•Pipistrellus bat coronavirus HKU5

•Rousettus bat coronavirus HKU9

•Severe acute respiratory syndrome–related coronavirus (SARS-CoV, SARS-CoV-2)

•Tylonycteris bat coronavirus HKU4.

 

Genus: γ-coronavirus (γ-coronaviruses mainly infect birds.)

 

Species:-

•Avian coronavirus

•Beluga whale coronavirus SW1.

 

Genus: δ-coronavirus (δ-coronaviruses also mainly infect birds although porcine δ-coronavirus is important in animal husbandry. It emerged in 2014 and may have spilt over from an avian host).

 

Species:-

•Bulbul coronavirus HKU11

•Porcine coronavirus HKU15

 

Classification of Coronavirus