This post is written with the intention to educate not only biotech or science students, but for the general population. Here we have written the basic information about the SARS-CoV-2. In the next post we will write about SARS-CoV-2 more in detail.
Here we go:
A virus is an extremely small parasite that infects a susceptible cell, and can direct the cell machinery to produce more viruses. It cannot reproduce on its own and needs a host cell to reproduce. A great variety of viruses can infect different hosts including animals, plants, bacteria and humans (see fig 1).
(Just for info: Read our previous posts on mode of replication of bacteriophages; lytic cycle and lysogenic cycle.)
When the virus infects an organism, it causes some disease or disorder in the same. Hence, virus has always been a matter of concern from the point of view of public health. Also, it can evolve and cause different symptoms or even attack a new hosts. In humans, virus can cause range of diseases, like common cold, measles, chicken pox, HPV, herpes, etc.
Recently, at the end of 2019, China was shaken by several cases of unknown type of pneumonia, which has now spread world wide. These cases were first observed in the people associated with Hunan seafood market in Wuhan city of China, where live animals such as bats, frogs, snakes, birds, marmots and rabbits are normally sold. It was further found that, the virus not only spread from the animals to human but also from human to human, through close contact with an infected person, via respiratory droplets or aerosols released during coughing or sneezing. These droplets or aerosols may be inhaled by another person and infect him.
– The name:
On investigation, these cases were found to be caused by a novel type of coronavirus, hence was called as novel coronavirus initially. Later the Chinese researchers named the virus as Wuhan coronavirus or 2019 novel coronavirus (2019-nCov) based on the place and year of the initial occurrence.
On further genome analysis, it was found that genomic sequences of this virus and SARS-CoV have extremely high similarity. SARS-CoV, too, had caused epidemic with symptoms including severe acute respiratory syndrome. Hence the virus was named by the International Committee on Taxonomy of Viruses (ICTV), as SARS-Coronavirus 2 (SARS-CoV-2) and the disease as ‘coronavirus disease 2019‘ (COVID-19).
(Just for info: Get the updated situation report of the virus by the WHO here.)
• Coronaviruses:
The SARS coronavirus (SARS CoV-2) belongs to the family of viruses called Coronaviridae (see below for taxonomical classification), collectively known as Coronaviruses. The viruses belonging to this family appear like crown or sun (corona in Latin) when observed under transmission electron microscope, due to the presence of the spikes (see fig 2).
They have positive single-stranded RNA (+ssRNA) as their genome and are zoonotic, that is they can be transmitted from among animals and humans. Coronaviruses (CoVs) can cause varieties of diseases, affecting respiratory, enteric, renal, and neurological system in their host.
In 2003, a coronavirus, named as Severe Acute Respiratory Syndrome coronavirus (SARS-CoV), infected many people in Guangdong province of China and caused pneumonia symptoms with a diffused alveolar injury which lead to acute respiratory distress syndrome (ARDS).
(Just for info: Read the article on SARS-CoV on WHO’s site)
In 2012, another coronavirus, named Middle East Respiratory Syndrome Coronavirus (MERS-CoV) was first reported in Saudi Arabia. This virus then spread to several other countries. It, too, caused severe respiratory illness, including fever, cough, and shortness of breath. In later stage, patients developed pneumonia, followed by ARDS and renal failure. This epidemic had resulted in many death.
(Just for info: Read the article on MERS-CoV on WHO’s site)
Now, in 2019-20, SARS-CoV-2 (see fig 3), again a coronaviruses, has caused pandemic world wide. They share about 96% nucleotide sequence identities Bat SL-CoV, suggesting its source of emergence. This virus is highly contagious and has lead to the complete lockdown of the world on whole. Two different major types of SAR-CoV-2, based on differences in SNPs, have been reported. These types have been designated as L and S. L type is more prevalent (∼70%), newer and aggresive than the S type.
(Just for info: Read this paper on the evolution of the SARS-CoV-2)
• SARS-CoV-2:
As mentioned, SARS-CoV-2 belongs to family of Coronaviridae, the taxonomical classification is given below:
Realm: Riboviria (RNA viruses)
Order: Nidovirales (1. positive-sense, single-stranded RNA genomes 2. Latin nidus means nest: production of a 3′-co-terminal nested set of subgenomic mRNAs during infection)
Sub order: Cornidovirineae (enveloped viruses)
Family: Coronaviridae (have an outer envelope bearing long club-shaped projections resembling a crown or the solar corona)
Sub-family: Orthocoronavirinae (infect mammals and birds)
Genus: Betacoronavirus (difference based on genetic and serological factors)
Sub genus: Sarbecovirus (has only one papain-like proteinase instead of two in the open reading frame ORF1)
Species : Severe acute respiratory syndrome-related coronavirus (difference in set of conserved domains)
Current name: Severe acute respiratory syndrome coronavirus 2.
– Virion Structure
Coronavirus virions, including SARS-CoV-2, are spherical, having a diameter of around 125 nm. The most prominent feature of coronaviruses, the club-shape spike projections, give them the appearance of a solar corona. These viruses have envelopes made up of lipid bilayer, within which enclosed is the symmetrical helical nucleocapsid (see fig 4). The nucleocapsid is made up of only one type of protein, the N protein, that binds the viral genome in a beads-on-a-string manner. This helps the viral genome to bind to the replicase-transcriptase complex (RTC), and packaging of genome into viral particles.
Coronavirus virus particles contain other four structural proteins, including the spike protein, membrane protein, envelope protein and the hemagglutinin-esterase (see fig 4).
Spike (S) glycoproteins form trimers which make up the spike on the surface of the virus. These spikes bind the cell membrane protein angiotensin-converting enzyme 2 (ACE2) and gain entry into the human cells.
The membrane (M) protein is the most abundant structural protein in the virion. It has 3 transmembrane domains and possibly responsible for the shape of the virion.
The envelope (E) protein plays important role in the assembly and release of the virus. It is not required for replication but is involved in pathogenesis of the virus. It also has ion channel activity.
The hemagglutinin-esterase has acetyl-esterase activity and can cause hemagglutination (agglutination of RBCs, can be used to detect presence of virus particles). This protein binds sialic acids on surface of the host cell and assists in the spike protein-mediated entry into the cell. It also helps the spread of virus through the mucosa.
• Symptoms of COVID-19:
The SARS-CoV-2 affects different people in different ways. A healthy person usually develops mild to moderate symptoms and recover without requiring special treatment. However a person with an underlying medical conditions and/or over 60 years of age, may develop severe disease or may even die.
According to WHO, the common symptoms of COVID-19 are fever, tiredness and dry cough, which occur after 2-14 days of exposure. Other symptoms of the disease includes shortness of breath, sore throat, aches and pains. Some people may experience diarrhoea, nausea or a runny nose.
Currently (March, 2020), there is no specific medication or a vaccine against the virus, hence the patients are being given treatment with non-specific therapeutic agents to ease the symptoms.
• Precautions
This virus is highly contagious and hence WHO has has suggested some basic protective measures against the SARS-CoV-2.
(Just for info: This article about how long the virus survives on different surface
1. Wash hands frequently: The hands should be washed thoroughly at regular intervals with soap and water or alcohol based sanitizers. This kills viruses on hand, if any.
2. Maintain social distancing: Distance of at least 1 metre (3 feet) should be maintained from any person coughing or sneezing. This helps is avoiding inhalation of liquid droplets which may contain virus. The person having any history of recent travel or mild symptoms should observe self isolation. Many nations are observing nation-wide lockdown and/or curfew to restrict crowding of people.
3. Avoid touching eyes, nose and mouth: These parts allow the entry of virus inside the body, if the hands are contaminated, and may infect the person.
4. Practice respiratory hygiene: The mouth and nose should be covered with bent elbow or tissue while coughing or sneezing. The used tissue should be disposed off immediately. This helps protect the people around from getting infected.
5. Seek medical care early in case of symptoms like fever, cough and difficulty breathing: Till medical help is provided, its wise to stay at home. This helps in preventing the spread of viruses and other infections.
6. Stay informed and follow advice by healthcare provider: Be aware of the lastest updates to avoid rumours and panic. Advice given by the healthcare provider and public health authority help one be safe and prevent spreading of this pandemic further.
For more informations on precautions kindly visit WHO site
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Be safe!! Be informed!!
And spread the information with your near and dear ones and anyone else!!
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Read other posts by The Biotech Notes:
Overview of Immune system: Innate and Acquired Immunity.
Clinical Trials (P-2): Randomization.
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References:
Cascella et al (2020) Features, Evaluation and Treatment Coronavirus (COVID-19). Treasure Island (FL): StatPearls Publishing.
Shereen et al (2020) COVID-19 infection: origin, transmission, and characteristics of human coronaviruses. Journal of Advanced Research (Journal Pre-proofs). DOI: https://doi.org/10.1016/j.jare.2020.03.005.
Fehr & Perlman (2015) Coronaviruses: an overview of their replication and pathogenesis. Methods Mol Biol. 1282:1–23.
Karhu, Nelli. (2006). The genome packaging machinery of dsDNA bacteriophage PRD1. Academic Dissertation; University of Helsinki.
https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html
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