Currently known as 2019-nCoV, the virus is understood to be a new strain of coronavirus not previously identified in humans. The Sars (Severe Acute Respiratory Syndrome) virus that killed nearly 800 people globally in the early 2000s was also a coronavirus, as is the common cold.
Authorities have said this new virus originated in a seafood market in Wuhan that “conducted illegal transactions of wild animals”. The market has been shut down since the beginning of the year.
Some researchers have suggested the illness may have originated in snakes. A study published on Wednesday in the Journal of Medical Virology said genetic analysis suggests snakes are “the most probable wildlife animal reservoir” for the virus, but this would need to be confirmed by other studies. Other researchers have questioned the theory.
There is also evidence of human-to-human transmission with the virus spreading from patients to family members and healthcare workers.
But understanding more about how the virus transmits between people is one of the major outstanding questions in this outbreak.
The virus infects the lungs, and symptoms start with a fever and cough. It can progress to shortness of breath and breathing difficulties.
The World Health Organization (WHO) emergency committee on Wednesday deferred a decision on declaring a “global emergency” over the new virus, but is meeting again on Thursday.
A global emergency is the highest level of alarm the WHO can sound, and has previously been used in response to swine flu, Zika virus and Ebola.
The World Health Organization (WHO) is alerted on 31 December 2019, by the Chinese authorities of a string of pneumonia-like cases in Wuhan, a city of 11 million people.
Patients are quarantined and work begins on identifying the origin of the pneumonia.
The US Centers for Disease Control and Prevention (CDC) identifies a seafood market suspected to be at the centre of the outbreak. It is closed on 1 January 2020.
On January 9, the WHO says that the outbreak in Wuhan was caused by a previously unknown type of coronavirus, which is a broad family ranging from the common cold to more serious illnesses like SARS.
To date 59 people have been infected of whom seven are in a serious condition, according to an official toll.
The Chinese health authorities say a first person has died of the virus on January 11.
They revise downwards the number of sick people to 41.
Spreads beyond China
On January 13, the virus spreads beyond China’s borders for the first time with a case emerging in Thailand, according to the WHO. The victim is a Chinese woman diagnosed with mild pneumonia who was returning from a trip to Wuhan.
On January 15 China’s health commission says no human-to-human transmission of the virus behind the Wuhan outbreak has been confirmed so far, but the possibility “cannot be excluded”.
The next day a first case of the virus is confirmed in Japan in someone who had stayed in Wuhan in early January.
On January 17, a second person, a 69-year-old man, dies in Wuhan, according to the authorities.
The same day, the CDC announces that it will begin screening passengers arriving from Wuhan at three airports: San Francisco, New York’s JFK and Los Angeles.
Human to human transmission confirmed
On January 20, a third death and more than 100 new cases are announced in China, sparking concerns ahead of the annual Lunar New Year holiday which begins January 25 and sees hundreds of millions of Chinese people travel nationwide.
The virus is present in Beijing in the north, Shanghai in the east and Shenzhen in the south. More than 200 cases have been recorded. The virus is also detected in South Korea in a Chinese person who has arrived by plane from Wuhan.
China’s President Xi Jinping says that the virus must be “resolutely contained”, in his first public comments on the outbreak.
Human-to-human transmission is “affirmative”, a top Chinese expert on infectious diseases Zhong Nanshan tells state broadcaster CCTV.