Unless you've been living in a bomb shelter for the past two months, it's unlikely you've not heard of COVID-19, commonly referred to as coronavirus.
Since emerging from its epicentre in Wuhan, China, in January, it has spread to more than 140 countries on six continents, with 138,959 confirmed cases and 5,111 deaths. More than 3,000 of those have been in China. Italy has had in excess of 1,000 deaths and Iran around 500.
Coronaviruses are zoonotic, meaning that they are transferred from animals to humans. Others you might have heard of include Severe Acute Respiratory Syndrome (SARS) - which was transmitted from cats to humans - and Middle East Respiratory Syndrome (MERS), which was transmitted from camels.
Scientists are already aware of several coronaviruses circulating in animals that have not yet been passed to humans. COVID-19, meanwhile, is a 'novel' coronavirus, meaning it is a new strain and has not been previously identified in humans.
The coronavirus is named for the fact the scientists that first looked at the virus under a microscope (back in 1968) thought that it resembled a "solar crown", the ring of gas that surrounds a sun.
Where did the virus come from?
The virus originated in Wuhan, a city of 11 million people in the central Chinese province of Hubei. Months on, the majority of the deaths - over 3,000 - have been in Hubei, while 51,553 people in the province have recovered, according to the Chinese authorities.
It is believed that the virus was transmitted via bats and that its epicentre was the Wuhan Huanan Seafood Wholesale Market. But the World Health Organization (WHO) has also suggested that the virus could have originated in pangolins, also known as scaly anteaters, an endangered species that is used in Chinese medicine.
Genetically, the new virus is 80% similar to SARS, which spread rapidly in 2002 and 2003 and killed 800 people.
What are the symptoms?
This new virus can, in more severe cases, cause pneumonia, severe acute respiratory syndrome and kidney failure.
Common signs of the infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties.
One of the problems with the coronavirus is that the symptoms can be mild, especially in younger, healthier people, similar in some cases to the common cold or seasonal flu.
As a result, some health authorities have urged people with symptoms not to go to their GP or an emergency room and instead to self-isolate for 14 days.
Another problem is that in some people - particularly children - the disease can be asymptomatic, but is still contagious.
Lastly, the disease is most deadly in people over 70 and those who have existing health conditions.
How is the virus transmitted?
The disease can be spread from person to person through moisture from the nose or mouth, which is passed on when an infected person coughs or sneezes.
That is why health authorities have warned people to stay at least a metre away from anyone who is sick, and advised those who are sick to cover their mouths when they cough or sneeze.
Droplets of moisture land on objects and surfaces around the person and are passed on when another person touches those surfaces or objects and then touches their nose or mouth.
What measures are countries taking?
In the early days of the virus, China put three cities -Wuhan, Huanggang and Ezhou - on lockdown: stopping outbound travel in an effort to contain the virus.
In Italy, which is the worst affected of all European countries with 15,000 cases and 1,000 deaths, the entire country is on lockdown, with schools, shops and public buildings closed.
Some of Italy's neighbours - including Austria and Slovenia - have restricted travel from the country.
On March 13, Spain announced a lockdown of four provinces in Catalonia, while the US has banned all arrivals from Europe for 30 days, except those from the UK.
In other countries, the response has been less drastic: Germany, which has over 3,000 cases, has resisted closing schools despite predictions from Chancellor Angela Merkel that up to 70% of the population could eventually be infected by the virus.
French President Emmanuel Macron announced on March 12 that schools across France would be closed and that gatherings of more than 100 people banned.
How long will it last?
It is the million-dollar question. Since the surge in cases in China in the early days of the virus, both cases and deaths have slowed in recent weeks. Between January 22 and February 19, cases went from zero to 75,000 in China. From February 23 to March 12, they have hovered around 80,000.
The Chinese authorities argue that this is due to an effective policy of containment, including heavy restrictions on travel for millions of people.
Italy, by contrast, is in the early stages of its outbreak: it had just three cases on February 15 and had more than 15,000 as of March 12. The spread in other European countries, including France, Germany and Spain, has been slower - but could still be to come.
Most estimates suggest that a vaccine for coronavirus is at least a year away, although scientists in Israel recently said that they were 'a few weeks' from developing one.