Brendan Bain | Learning more about SARS-CoV-2 viruses can help to slow spread of COVID-19
Understanding how the Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2) gets into our bodies is vital if we are to succeed in preventing this virus from continuing to spread and giving so many of us coronavirus disease 2019 (COVID-19).
The SARS-CoV-2 virus is new, but it belongs to a bigger family of coronaviruses that includes some of the viruses that cause the common cold. But SARS-CoV-2 viruses are different from common cold viruses because of the severe damage that SARS-CoV-2 viruses can do in some persons’ bodies. Thankfully, in most cases, the immune system in our bodies will eventually bring these viruses under control. But we cannot assume that this will happen in every case, so it’s important for us to focus on preventing contact with these viruses.
FIRST TARGETS OF SARS-COV-2 VIRUSES
The first targets of SARS-CoV-2 viruses are cells lining the nose and the throat. These viruses can reach their targets easily when droplets from an infected person are passed to the nose or throat of someone else. This happens when the infected person stays close to others. Sharing of droplets happens when persons who are infected cough, sneeze, talk, sing, shout, laugh or spit at close range. The longer the period of close contact, the greater the risk of spread.
SARS-CoV-2 viruses can also be spread via air that lingers in closed spaces when persons who are carrying these viruses expel infected droplets into the air. Closed spaces that can be contaminated in this way include air-conditioned rooms, elevators and air-conditioned cars, buses and airplanes.
Hand-to-hand contact with someone who is infected with SARS-CoV-2 is another way that can result in spread of this virus because hands can become contaminated from contact with the nose and mouth. In addition, surfaces, for example, doorknobs or door handles and desk or counter tops used repeatedly by many persons can contaminate our hands and the viruses can then be passed from hand to nose or mouth. Research is also showing that SARS-CoV-2 viruses can survive in the bowel of an infected person and can pass out in the person’s faeces. This means that public toilets are a possible source of these viruses. It is recommended that public toilets should be covered before they are flushed to avoid release of droplets during flushing.
SARS-COV-2 VIRUSES ARE PARASITES
Like other viruses, SARS-CoV-2 virus are classified as parasites because they rely and depend on their host for their survival. Viruses need a living host – human, animal, plant or bacterium– in order to survive.
Viruses are invisible to our normal eyesight because of their very small size. To see them, we need to use the magnification (enlargement) of very powerful microscopes. The photographs that are shown in magazines and on television help us to appreciate that these viruses are real, and these photographs are taken from microscopes – the pictures are greatly magnified.
In nature, a single virus operating alone is usually unable to succeed in causing an infection in its potential host. In the case of human viruses, the natural defences of the human body are normally able to shake off or neutralise small numbers of virus particles. This is true of SARS-CoV-2 viruses. So, the danger is from a group of viruses or a ‘viral load’. If a sufficiently large number of SARS-CoV-2 viruses gets placed at their first target sites, they are then able to survive and multiply in the cells of the host. The viruses act like hijackers and take over the resources – the energy and mechanics – present in the person’s cells.
Once the group of these hijacking viruses gets into the target cells of the nose and throat, they disrupt and redirect these cells to do virus work. Redirection of the infected cells causes the cells to malfunction and, at the same time, allows the viruses to multiply. Eventually, large numbers of virus offspring break free from the cells in the nose and throat and spread to the lungs and other parts of the body where they can also cause damage.
A comparison is found in the world of computers and cell phones. Certain types of computer or cell phone viruses act by disrupting and redirecting the computer or phone to do virus work. In the process, these viruses cause damage to computers and phones.
The receptor for SARS-CoV-2 viruses is
angiotensin conversion enzyme 2, known as ACE2.
Doctors Krishna Sriram, Paul Insel and Rohit Loomba at the University of California in San Diego have given a clear description of how groups of SARS-CoV-2 viruses in sufficient numbers begin to work. According to these researchers, thinking of an individual SARS-CoV-2 virus, “Using the spike-like protein on its surface, the SARS-CoV-2 virus binds to an ACE2 receptor on the surface of the human target cell, like a key being inserted into a lock. This is the first step leading to entry and infection of the human cell. Hence, the ACE2 receptor acts as a cellular doorway for the virus that causes COVID-19.”
Recently, when discussing the lock and key idea with Radio Jamaica hotline host, Dr Orville Taylor, he reminded me that two “Velcro” surfaces hook and bind tightly to each other. The Velcro illustration is even more powerful than the lock and key idea because the Velcro mechanism captures the fact that several SARS-CoV-2 particles can be attracted to several ACE2 receptors at the same time.
In addition to the binding between the spike protein of the SARS-CoV-2 virus and ACE2, research scientists have discovered another protein enzyme on the surface of the cells in the nose and throat which activates the spike protein and helps it to fuse to its target cells, enabling the viruses to enter these cells. The process of activation of the spike protein of the virus is called priming. The priming enzyme is called transmembrane serine protease 2 (TMPRSS2).
LET’S TAKE PREVENTIVE ACTION BASED ON WHAT WE KNOW
We have learned that COVID-19 is caused by SARS-CoV-2 viruses, which enter our bodies via the nose and throat. These viruses can be passed easily to unprotected persons at close range.
National Public Health authorities have issued policies and programmes aimed at limiting the spread of SARS-CoV-2. Researchers in many countries are studying treatments for COVID-19 and others are trying to find effective vaccines to limit the further spread of the disease. Laboratory staff are doing tests every day to identify persons with COVID-19 in time to get them treated and healthcare teams are busy treating persons who are battling the infection.
In the meantime, every member of the public must consider ourselves part of the anti-COVID team. We must play our part in preventing ourselves from catching and continuing to spread SARS-CoV-2 viruses by taking the following actions regularly:
• Wear a face mask to cover mouth and nose when around other persons, especially in closed spaces with poor air circulation.
• Keep safe physical distance from one another (at least six feet) in public.
• Avoid spending long periods of time in closed spaces with other persons.
• Avoid unnecessary group gatherings.
• Wash hands frequently with soap and water, so that if you touch your nose or mouth, your hands are clean.
• If soap and water are not available, use approved hand sanitisers containing at least 60 per cent alcohol (ethanol or isopropyl alcohol) regularly.
• Avoid shaking hands with other persons because we don’t know whether we ourselves or other persons are carrying the SARS-CoV-2 virus.
Improving our knowledge is the first step in preventing COVID-19 infection. But research on human behaviour often shows a gap between the number of persons who know about a disease and the number of persons who take correct and consistent action to prevent the disease. This gap can spoil our safety as individuals, communities and countries. This article is meant to warn us against falling into the knowledge-behaviour gap.
Brendan Bain is an honours graduate of the Faculty of Medicine, University of the West Indies (UWI), and a former Wellcome Trust Fellow in Clinical Infectious Diseases. He now serves as an honorary consultant physician and as a member of the COVID-19 team at the UWI. Email: email@example.com.