A coronavirus is a common type of virus that usually causes mild illnesses, such as the common cold. However, certain types of coronavirus can infect the lower airway, causing serious illnesses like pneumonia or bronchitis. Most people get infected with coronaviruses at some point in their lives and the majority of these infections are harmless.

Coronaviruses are enveloped viruses with extraordinarily large single-stranded RNA genomes of approximately 26 to 32 kilobases. Coronavirus particles usually appear spherical, as seen under an electron microscope, with a crown or “corona” of club-shaped spikes on their surface.

Two types of human coronavirus – Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV) – are known to commonly cause severe symptoms.

SARS-CoV first emerged in 2002-2003 in Guangdong, China as an unusual pneumonia, which developed into life-threatening respiratory failure in certain cases. The virus rapidly spread across 29 countries, infecting more than 8000 people and killing about 800.

The MERS-CoV epidemic appeared in Saudi Arabia in 2012, with people experiencing similar symptoms to SARS-CoV but dying at a much higher rate of 34 per cent. Unlike SARS-CoV, which spread quickly and widely, MERS-CoV has been mainly limited to the Middle East. Coronaviruses can infect other animals, in addition to humans, and dromedary camels are a major animal source of MERS-CoV infection in humans.

In early January 2020, cases of an illness similar to SARS and MERS were reported in Wuhan, China. The cases could all be traced back to a large seafood and animal market in Wuhan. The virus has since been identified as a new coronavirus, and cases have been reported outside China.