What Is Coronavirus?
Every day, new facts, innovations, and statistics are emerging related to the ongoing novel coronavirus pandemic. The infection that began in Wuhan in China reportedly in December of 2019 has now spread all across the world, prompting nationwide lockdowns and social distancing measures.
Coronavirus disease is a newly discovered infectious disease. Primarily spread through droplets when an infected person sneezes or coughs, COVID-19 typically causes mild to severe respiratory symptoms.
The official name of coronavirus disease is COVID-19 (Coronavirus disease discovered in 2019). The virus that causes this disease is called ‘severe acute respiratory syndrome coronavirus 2’ or SARS-CoV-2.
While not much is known about the way the new coronavirus behaves, researchers have been able to identify the structure of the virus, the way it binds to human respiratory cells, and the possible drug/vaccine candidates.
The official name of coronavirus
Viruses, just as the diseases they cause, have different names, and are given names based on their genetic structure. This helps in developing medicines, vaccines, and diagnostic tests for the particular virus. The ICTV ( International Committee on Taxonomy of Viruses) is the international body that names viruses. Diseases, on the other hand, are named officially by the World Health Organization (WHO).
The coronavirus family of viruses is a large group of viruses. They cause diseases in mammals and birds. From the common cold to severe respiratory tract infections, coronaviruses can cause many illnesses in humans. Two of the severe diseases caused by coronaviruses in the past were SARS (Severe Acute Respiratory Syndrome) and Middle East Respiratory Syndrome (MERS). (WHO, 2020). While the SARS outbreak originated in China in 2002, MERS was reported first in 2012 in Saudi Arabia. (Centers for Disease Control and Prevention [CDC], 2019).
On February 11, 2020, ICTV named the new virus that caused an outbreak in Wuhan, China, as SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). SARS was chosen in the name as the virus is related genetically to the coronavirus that caused the 2003 SARS outbreak. The same day, the World Health Organisation (WHO) announced the name of the disease caused by SARS-CoV-2 as “COVID-19.”
How are viruses classified?
Coronaviruses belong to the Coronaviridae family under Nidovirales order. Members of the Coronaviridae family cause wide-ranging liver, respiratory, intestinal, or neurological diseases in many animals such as cats, bats, cattle, and camels. About seven human coronaviruses are capable of causing infections in humans. While some of these viruses were identified in the 1960s, others have been detected only in the 21st century.
Human coronaviruses cause common colds as well as upper respiratory infections that are self-limiting in otherwise healthy individuals. These viruses can cause lower respiratory tract infections in the elderly as well as immunocompromised people (those with HIV/AIDS, people who are on immune-suppressing drugs to prevent rejection of an organ after an organ transplant).
Other coronaviruses, including SARS-CoV-2, SARS-CoV, and MERS-CoV, cause epidemics that vary in severity. These viruses cause respiratory infections and can also involve non-respiratory organs.
Structure of coronavirus
Viruses have an outer envelope made of phospholipids (these are a type of fats present in all cell membranes) and proteins, or, at times, only a protein coating called the capsid. Inside this envelope or layer lies the nucleic acid. Viruses can also, at times, contain enzymes that are a form of proteins. (“Viral Evolution, Morphology, and Classification,”n.d.).
Coronaviruses are viruses that have an outer envelope and a single-stranded RNA. Coronaviruses are spherical in shape and measure 120 to 160 nanometers in diameter. When viewed under an electron microscope, there is an appearance of the solar corona or crown around the virus particles. These coronas are the result of club-shaped protein projections on the virus that has led to the virus being named ‘coronavirus.’ (Science Direct, 2012).
How does coronavirus attach itself to cells in the human body?
Though the virus makes use of many different proteins to make copies of itself and to enter the human cells, the spike proteins on its surface are the primary tool the virus uses to bind to a ‘receptor.’ The receptors are a protein present on the cell surface of the host (the infected human) and functions as a doorway to the cell.
When the spike protein binds to receptors of the human cell, the membrane or covering of the virus fuses with the cell membrane of the human cell and allows the virus genome to enter into the host cell to start the infection. (National Institute of Allergy and Infectious Diseases [NIAID], 2020).
In a research paper published in the Science journal, scientists at Austin-based University of Texas highlighted the identification of the spike protein that is called S-protein. (National Institutes of Health [NIH], 2020).
Later, researchers also identified the ‘gateway’ in the respiratory cells called ACE2 (angiotensin-converting enzyme) receptor protein and the way these two proteins interact to cause disease. In simple terms, this interaction is a lock and key mechanism.
The spike protein (S protein) acts as a tiny ‘molecular key,’ whereas the ACE2 receptor protein is the ‘doorknob’ for the door of body cells. The spike protein latches on to the doorknob and opens it, thus entering the body cells to cause the infection. (Wrapp, et al. 2020)
A researcher compared the human body to a house while the robber was the SARS-CoV-2. ACE2 is the doorknob at the door of the house. Once the spike protein (S-protein) grabs the doorknob, the virus can enter the house. (Pappas, 2020).
When a person inhales droplets from an infected person’s cough or sneeze, the virus enters the throat and nose. Scientists have found that the virus finds a welcome home in the nose lining because these cells are abundant in ACE2 receptors. ACE2 receptors are present in cell membranes of lungs, heart, kidneys, intestine, and arteries. While these enzymes regulate blood pressure, they are vulnerable to the SARS-CoV-2 attack.
Once the virus enters the nose, it starts to multiply and continue to march down the windpipe to enter the lungs if the immune system does not fight back at this stage. The virus enters the lungs through alveoli, the thin and distant air sacs in the lung that has plenty of ACE2 receptors. (Wadman et al., 2020).
However, the virus does not affect heart cells, although these cells are also rich in ACE2 receptors. Scientists believe other co-receptors may be involved in allowing entry of the virus into cells in the lungs. (Makin, 2020).
Is the virus mutating?
Chinese researchers analyzed 103 available genomes of the coronavirus and the findings of this study published in the National Science Review of the Chinese Academy of Sciences (CAS) in March of 2020. The study found that the novel coronavirus had mutated into ‘S’ and ‘L’ sub-types.
- The L type accounted for 70 % of cases.
- S type linked to 30% of cases.
- The L type is ‘more aggressive’ and more easily transmissible (Tang et al. 2020).
More recent research, still undergoing peer review indicates a substantial likelihood that the virus has mutated into 30+ strains, differentiated from the primary infection to various degrees.
How did COVID-19 transfer to humans?
The outbreak reported first in Wuhan in the Hubei province of China, in a live animal market. Bats are the most common carriers of coronaviruses, although they typically do not directly transmit the virus to humans. Some illnesses, such as the one caused by the Nipah virus, are linked to direct human contact with the urine, faeces, or saliva of bats.
Transmission of coronavirus from bats to humans is thought to have occurred through an intermediary animal, such as pangolin. Researchers in China recently suggested that the initial source of the pandemic could have been pangolins as the genomic sequence of SARS-CoV-2 was 99% similar to the coronaviruses found in pangolins. (Sandoiu, 2020).
Human transmission of the SARS-CoV occurred through civet cats in 2003, while dromedaries (Arabian camels) were the source of MERS virus transmission. It is still not clear if bats or pangolins are the sources of COVID-19.
How does it spread between humans?
In humans, the novel coronavirus spreads mainly through tiny droplets produced when a person infected sneezes or coughs. These droplets that contain the virus can enter the noses or mouths of other people nearby. Scientists also believe the viruses are inhaled (aerosol transmission) when a person breathes in.
Typically, viruses spread either through airborne droplets or through aerosols. Larger droplets that settle down to the ground are called droplets. Droplet nuclei particles that are smaller in size with the aerodynamic diameter being less than 5μm remain are called aerosols. These aerosols remain in the air for more extended periods. Aerosols can infect another person who is exposed to these smaller droplets, but get destroyed quickly based on environmental conditions such as heat.
There is a higher risk of person-to-person transmission when people are within six feet or two metres of each other. The virus can also linger on surfaces such as metal doorknobs, taps, or others. (WHO, 2020).
How long does it last on different surfaces and in aerosols?
Coronavirus, according to a study conducted by National Institutes of Health (NIH, 2020), stays on surfaces and in aerosols for anywhere from few hours to few days. Scientists found that the virus lingers in aerosols for three hours. The study also found the virus stays:
- On copper – up to four hours.
- On cardboard – up to 24 hours.
- Stainless steel: two to three days.
- Plastics: two to three days.
- Aerosols – up to three hours.
How far can the virus travel as aerosols?
In a letter to the White House Office of Science and Technology Policy, the National Academy of Science, Engineering and Medicine states that coronavirus that causes COVID-19 may spread through aerosols. The report cites a study where the virus was detected on-air and surfaces as far as six feet away from infected patients in isolation rooms. (The National Academy of Science, Engineering and Medicine, 2020).
Another study conducted in Beijing found the virus droplets in aerosols can travel for up to four meters (13 feet) from infected patients. (Guo et al., 2020). It is noted, the concentration of the virus particles (in parts per billion) decline severely further away from the source.
With proper precautions, the use of face mask by the infected person and so on, the virus spread is severely limited, confirmed in a recent study where the virus aerosol concentration (parts per billion) was very low near where COVID-19 patients (Ong et al., 2020).
More research is currently underway to understand and confirm how far coronavirus aerosols can travel.
Can the virus spread through food?
Currently, experts agree that coronavirus does not spread through food. Hygienic food handling practices are, however, recommended to minimize the risk of food-borne illnesses. (U.S. Food and Drug Administration. [FDA], 2020).
Can the virus spread through pets?
Laboratory studies have shown that cats, dogs, and ferrets are susceptible to the disease. However, according to the World Organisation for Animal Health, (2020), there is no evidence that COVID-19 can spread through pets.
What are the common Symptoms?
Emerging reports suggest that many people with COVID-19 are asymptomatic (have no symptoms) but can still transmit the virus.
Analysis of data in China also indicates that for an infection to occur, close contact is necessary between individuals. The spread is limited, according to this data, to healthcare workers, family members, and other close contacts.
The incubation time (the time it takes for symptoms to appear after getting infected) varies from three to seven days, while it can also take up to two weeks. This data showed that the R0 (R nought) of this virus is 2.2, which means each person infected with COVID-19 transmits it to 2.2 more individuals. R0 of the 2003 SARS-CoV was three.
As evident from the Chinese Centers for Disease Control and the WHO (World Health Organization) reports, the clinical symptoms of COVID-19 can be of three levels.
This level of severity is associated with septic shock (the infection affects the entire body), respiratory failure, and multiple organ failure/dysfunction. About 5% of cases developed a critical illness. (Cascella, et al., 2020).
People with severe illness present pneumonia with fever, severe dyspnea, fast heartbeat (tachypnea), and respiratory distress resulting in lowered blood oxygen saturation. Close to 14% of cases developed an acute illness.
Mild symptoms of COVID-19 are associated with the infection of the upper respiratory tract. These include dry cough, mild fever, nasal congestion, sore throat, headache, malaise, and muscle pain. The symptoms of severe illness, such as difficulty with breathing, are not present in these individuals. Some people also experience diarrhoea and stomach pain, although this is rare.
People with moderate illness complain of respiratory symptoms, including shortness of breath and cough without severe pneumonia.
What is the cure for coronavirus?
With scientists, biotech firms, and pharma companies working at record speed to find a cure for COVID-19, it is only a matter of time until a medication or vaccine emerges. Until then, precaution is the best cure. Practising social distancing, cough etiquette, and consulting a healthcare provider, if infected, are the best ways to stay safe.
How dangerous is coronavirus?
81% of people with COVID-19 present mild to moderate form of the illness and recover on their own. 14% of cases were severely marked by laboured breathing and a decrease in blood oxygen levels. About 5% of COVID-19 cases were critical with septic shock, respiratory failure, and multiple organ dysfunction or failure.
While all ‘severe’ patients recovered, 50% of ‘critical’ patients died. The mortality rate, in this study, was 2.3%. (The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team, 2020).
How is coronavirus diagnosed?
Real-time fluorescence or RT-PCR test is used to detect the presence of SARS-CoV-2 in throat swabs, sputum, and lower respiratory tract secretion samples. After collecting the sample, it is treated with chemical solutions to remove fats and proteins in the sample, leaving behind only the RNA of the virus.
The RNA is a one-strand molecule, which makes proteins that enable the virus to stay alive and function. The SARS-CoV-2 virus is made up only of RNA, and to detect its presence in the sample, scientists first convert RNA to DNA (double-stranded molecule) using an enzyme.
They then add short DNA fragments that act as marker labels that attach themselves to viral DNA if the virus is present in the sample. The RT-PCR machine creates samples with billions of copies of the viral DNA.
A fluorescent dye is added to the sample, which binds to the marker labels (short DNA fragments) present on viral DNA. When the light of a specific wavelength is present, the fluorescent dye reflects the light in a different fluorescent wavelength.
The intensity of the reflected fluorescent light above specified thresholds indicates the presence of the COVID-19 virus (Jawerth, 2020).
What is the recovery time for coronavirus?
According to the WHO, the approximate median recovery time for mild cases from onset to complete clinical recovery is two weeks. For severe or critical forms of the disease, the recovery time can be between three and six weeks. (Report of the WHO-China Joint Mission on Coronavirus Disease 2019, 2020).
Who is most at risk for coronavirus?
People above the age of 60 years and individuals with underlying conditions, including diabetes, hypertension, chronic respiratory disease, cancer, and cardiovascular disease, are at increased risk for the severe form of the disease. The risk of the virus infecting children is low, and disease in children, according to WHO, is relatively rare, while symptoms for those affected are mild. People below the age of 19 with severe or critical disease is also low at 2.5% and 0.2%, respectively.
Mortality risk appears to increase with age, and people above 80 years of age have the highest mortality risk. Males also have a higher risk of mortality as compared to females. Smokers also may be more vulnerable to coronavirus infection as they may have reduced lung capacity. (Report of the WHO-China Joint Mission on Coronavirus Disease 2019, 2020).
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