Archives / july 2021

Dr. Sajitha Jasmin S L, MDS(OMR)

The Coronavirus disease 2019 (COVID-19) outbreak in Wuhan city, China has been announced as a pandemic on 11 March 2020 by World Health Organization (WHO), because the disease spreads all over the world. As the infection is airborne, it can easily be transmitted to others during close contact mainly through respiratory droplets formed by coughing sneezing, and talking. Bronchoalveolar lavage samples were collected from patients with pneumonia of unknown etiology and the causative agent identified throughReal-time Polymerase Chain Reaction (RT-PCR) assays as a Beta coronavirus and named it a Novel Coronavirus. Due to the higher transmissibility, increased infectivity and lack of effective treatment and vaccine, the fatalities are increasing day by day globally. As the Dentists are medical professionals who are working close to the patients, they are at the bilateral risk of getting and transmitting infections thereby several dental care facilities in the affected countries have been closed or providing minimal treatment for emergency
cases. This article series reviews the Coronavirus in general, COVID-19 pandemic, prevention, diagnosis, and management, and the importance of Dental care during this ongoing pandemic.

1. Introduction
2. Origin and evolution
3. Structure
4. Classification
5. Human Coronaviral- Diseases
6. Summary


Viruses are submicroscopic infective agents that can only live and replicate inside the living cells of an organism. They are usually identified and classified by culture, electron microscopy, and serological studies. There are so many species of viruses are causing diseases in humans till today and some of their infectivity is due to the environmental effects. The usage, “I got a cold” is indicated the altered and cold environment, promotes the growth of viruses like Influenza and Rhinoviruses that cause disease like the common cold. Also, lifestyle plays a role in the case of HIV. The smallpox pandemic has killed around 500 million people worldwide and up to 10% of the world;s population died in bubonic plague. Coronaviruses are enveloped viruses of 60-160
nm in diameter and infect many birds and mammals, including humans, causing respiratory tract, enteric, hepatic, renal, and central nervous system diseases of varying severity. In human beings, coronaviral infection is mainly associated with upper and lower respiratory tracts.

2. Origin and Evolution

The incidence of severe respiratory infection of chicken in the mid-1930s was thought to be the earliest known disease by coronaviruses, at present it;s known as avian infectious bronchitis, caused by avian infectious bronchitis virus (IBV). The human coronaviruses identified in the year 1965, in which the common cold was transmitted by nasal secretion that did not contain rhinoviruses, and further study of nasal swabs from these patients had demonstrated the presence of enveloped RNA viruses with the features similar to the previously defined infectious bronchitis virus.

The name “coronavirus,” coined in the year 1968, because of the presence of “corona”-like or crown-like structure on its surface by electron microscope examination. Coronaviruses are the largest known RNA Viruses (CoVs) belong to the family Coronaviridae, subfamily coronavirinae in the order nidovirales. (The family coronaviridae composed of two subfamilies, the Coronavirinae and the Torovirinae.) Coronaviruses were considered as minor pathogens of humans and caused 15%- 25% of all “common colds, until the outbreak of Severe acute respiratory syndrome (SARS) in 2002 by a new Coronavirus named as SARS Coronavirus (SARS-CoV). In 2015 another coronavirus distinct from SARS-CoV was isolated during theoutbreak of severe respiratory disease in the Middle East, called Middle East respiratory syndrome coronavirus (MERS-CoV) responsible for severe respiratory illness. The outbreak of Coronavirus disease (COVID-19), by a new strain of Coronavirus called Novel Coronavirus, also named Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) identified in December 2019 at Wuhan, China is the cause of the ongoing pandemic.

3. Structure

Members of the Coronavirus family are roughly spherical enveloped particles containing single- stranded positive-sense RNA genomes ranging in size from 27–33 kb. The genome encodes the structural proteins, including membrane(M), envelope(E), spike (S), and nucleocapsid (N), which are common to all coronaviruses. Studies have shown that the proteins encoded by these genes could be modulators of pathogenicity in the natural hosts. Some Coronaviruses have an additional membrane protein with hemagglutinating and esterase activities, called HE. The diameter of the virus particle is around 60-160 nm with an average of 74 spikes of 12-20 nm long over its surface. Surface spikes are homotrimers of the S protein which is composed of S1
and S2 subunits. The viral envelope consists of a lipid bilayer in which the membrane, envelope, and spike structural proteins are anchored.

4. Classification

Coronaviruses belong to the family Coronaviridae, subfamily Coronavirinae, and the order Nidovirales, with four genera—alpha (α) coronavirus, beta (β) coronavirus, gamma (γ) coronavirus, and delta (δ) coronavirus. The α and β coronaviruses infect mainly warm-blooded animals lead to respiratory disorders in human and gastrointestinal disorders in animals. The γ and δ coronaviruses infect birds, but some of them also infect mammals. Domestic animals can act as an intermediate host to transmit these viruses to humans. At present many species of α and β coronavirus have been identified in bats.

5. Human Coronaviral Diseases

There are Seven Human Coronaviruses are identified so far and only six of them were known to be responsible for respiratory diseases in humans until the outbreak of COVID- 19 in December 2019. In that four human coronaviruses (HCOVs) are endemic (Constant occurrence of a disease in a community) worldwide and cause 10-30% upper respiratory infections. They are, HCoV-229 E, OC43, NL63, and HKU 1. The other two are Severe Acute Respiratory Syndrome Coronavirus (SARS- CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) known to infect the lower respiratory tract. Severe acute respiratory syndrome (SARS) outbreak in 2002, the Middle East respiratory syndrome (MERS) outbreak in South Korea in 2015, and most recently, a novel coronavirus (SARS-CoV-2, also known as COVID-19) outbreak in China in December 2019, responsible for COVID 19 Pandemic and it causes great harm across the world.
Among the Human Coronaviruses 229E & NL 63 belong to the alpha(α) genre and others(OC43, HKU, SARS- Co V, MERS- CoV, and COVID-19) belong to the beta(β) genre. The mode of transmission of Coronavirus is mainly through respiratory droplets during close contacts.

6. Summary

A. Classical coronaviruses consist of a group of large, enveloped, single-stranded RNA viruses.
B. Alpha coronaviruses and beta coronaviruses cause respiratory disorders in human and gastrointestinal disorders in animals.
C. Animal-to-human and inter-human transmissions are frequently seen in these groups of viruses.
D. Recently, a new coronavirus named COVID 19 emerged at Wuhan, China belongs to the beta genre responsible for the ongoing Pandemic.

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