COVID-19 is a disease that affects people who have been infected by the SARS-CoV-2 virus, also called ‘coronavirus’. The name COVID-19 comes from the virus that causes it, and the year that it was first reported: COronaVIrus Disease – 2019.

As the new coronavirus spreads across the world, it is important that its behaviour is measured and monitored. The more we can learn now, the better prepared we can be to manage a pandemic like this in the future. Researchers are focusing on how the virus moves through the population, so that we can slow the spread of the disease, but they are also gathering information on how the virus moves through the individual. Knowing how the virus affects the body is important to help scientists develop a vaccine or a cure.

SO HOW DOES THE CORONAVIRUS ACT IN THE HUMAN BODY, AND WHAT HAPPENS TO YOUR LUNGS WHEN YOU GET COVID-19?

An airborne droplet from the cough of an infected person carries millions of virus particles. When breathed in, this droplet deposits its tiny virus particles on the mucus-coated inner surfaces of the human lung.

Coronaviruses are smaller than our lung cells and are all covered in spike-shaped proteins. These proteins are similar in shape to others that exist in the human body – this ‘disguise’ allows them to enter the lung cell on contact. Two key events now occur:

• The virus hijacks the healthy cell. It is flooded with the genetic material of the virus. The processes that normally help the cell make new cells (which are needed for growth, cell repair, and to keep you healthy) now make thousands of copies of the virus.
• The spike proteins on the surface link this hijacked cell to other nearby cells, and now the virus can invade these, too.
  This process repeats all through the lung, and new virus particles burst out of the cells into the mucus and the blood. The hijacked cells die, and many fragments of dead cells enter the blood. This is detected by the immune system.

The immune system responds by attacking and killing cells that have been infected by the virus. When this happens, the body’s temperature often rises, and the lung tissues become inflamed. The infected person may now feel very hot and have a persistent cough. For some people, these may be the worst symptoms they experience, and they will start to recover. ­

THE WORST CASE SCENARIO

In other cases, the lungs become so inflamed that it’s hard for a person to breathe. The coronavirus can infect the lining of the air sacs of the lungs. If this lining is damaged, the air sacs fill with fluid. This makes it very difficult for the body to get the oxygen it needs.

In this severe case, the infected person has pneumonia, and may need treatment in a hospital to support their breathing. This support may include oxygen, or in the most severe cases a machine called a ventilator. However, there is currently a shortage of ventilators (and the doctors and nurses to use them) in many countries, so this treatment may not be available to all patients.

There is still a lot that we do not understand about exactly how Covid-19 damages the lungs and other organs. One theory is that in the most severe cases the immune system becomes overwhelmed. White blood cells (the cells of the immune system) release molecules called cytokines. Too many of these molecules in the blood causes an extreme, uncontrolled reaction called a cytokine storm. This causes inflammation of multiple organs, including the heart. Recent studies have suggested that this can happen in patients with COVID-19. Along with the shortage of oxygen due to breathing difficulty, it means that many organs start to fail, causing death. Another theory is that Covid-19 damages the lining of tiny blood vessels in the body, causing many tiny blood clots which stop organs getting the oxygen they need. Understanding exactly what happens in these severe cases will be critical in finding treatments for the virus.

Thankfully, this worst-case scenario does not happen to every person who catches coronavirus. However, until researchers can find a vaccine or a cure, it is the responsibility of every person worldwide to attempt to reduce its transmission, by covering your mouth when you cough and washing your hands.