Covid-19 is a new coronavirus, a family of viruses that includes SARS and MERS and one that is also responsible for up to 30 per cent of common colds.
The disease is spreading rapidly across the globe because we have no natural immunity, and at present around one per cent of cases appear to be fatal.
This means that Covid-19 is around 10-times more deadly than seasonal flu. It is most serious for the elderly and vulnerable – especially those with underlying health conditions.
The virus is spread through droplets sprayed into the air by an infected person when they cough, sneeze, talk or laugh.
Some of the droplets will be small enough to pass through a simple face mask, others will land on surfaces where they can live for hours or sometimes days.
When breathed in, the virus particles travel through your nose and throat and attach to cells in the mucus membranes at the back of your throat and further down into your lungs.
Dr William Schaffner, infectious disease specialist at Vanderbilt University Medical Center in Nashville, told the New York Times the virus then hijacks your immune response and causes your body to produce more of the disease.
As the disease multiplies it infects neighbouring cells in your throat – causing that soreness, inflammation and dry cough.
If the virus mainly infects your throat and the upper respiratory tract that is when you will experience symptoms like a bad cold or flu.
Prof John Wilson, president-elect of the Royal Australasian College of Physicians, told The Guardian that ‘minor symptoms’ are a result of the disease infecting the upper part of your respiratory tract – a fever, cough and headache.
As it moves down your throat into your lungs, the membranes of your lungs become inflamed and damaged, making it harder for you to take in oxygen and breathe out carbon dioxide.
If the swelling and lack of oxygen cause the deepest parts of your lungs to fill with fluid and dead cells you can develop pneumonia, a serious infection.
X-rays show Covid-19 creates ‘ground glass opacities’ – opaque areas of damage and infection in the lungs.
It is this pneumonia which is the most serious symptom of coronavirus, making it increasingly difficult for people to breathe.
Prof Wilson says this is the ‘usual cause of death’.
While the virus focuses on the lungs, it can spread throughout your body, including your gastrointestinal system where it can cause diarhea.
You can see inflammation in the bone marrow and vital organs, according to Dr George Diaz of Providence Regional Medical Center in Everett, Washington.
The inflammation can prevent those organs working properly.
15 to 20 per cent of those who contract Covid-19 have a serious case, and in around one per cent of cases it proves fatal.
The elderly and vulnerable are among those most likely to develop a severe case.
Various medications and combinations are being trialed across the world, but at present in hospital the key treatment is to place patients on ventilation and ensure they have a high level of oxygen going into their lungs until they are able to function normally.