Beijing: A new SARS-like virus has killed 41 people, infected hundreds and reached as far as the United States, with fears mounting about its spread as hundreds of millions travel for Lunar New Year celebrations, which start Friday.
Many countries have stepped up screening of passengers.
Here's what we know so far about the virus:
It's entirely new
The pathogen appears to be a never-before-seen strain of coronavirus - a large family of viruses that can cause diseases ranging from the common cold to Severe Acute Respiratory Syndrome (SARS), which killed 349 people and another 299 in Hong Kong between 2002 and 2003.
Arnaud Fontanet, head of the department of epidemiology at the Institut Pasteur in Paris, told AFP the current virus strain was 80 per cent genetically identical to SARS.
It has been named "2019-nCoV".
It's being passed between humans
The WHO said Monday it believed an animal source was the "primary source" of the outbreak, and Wuhan authorities identified a seafood market as the centre of the epidemic.
There was evidence the virus is now passing from person to person, without any contact with the now-closed market.
More than 1,287 cases of the virus have now been reported, according to officials. Li Bin National Health Commission representative on Wednesday said 1,394 people were still under medical observation.
Nathalie MacDermott of King's College London said it seems likely that the virus is spread through droplets in the air from sneezing or coughing.
They also suggested the natural reservoir of the virus is likely to be bats.
Although the full genome sequence has been released, the origin and transmission mechanism of the novel coronavirus (2019-nCoV), as denoted by the World Health Organization, remain unclear.
So far, six whole sets of 2019-nCoV genomes have been released.
In a study published online by SCIENCE CHINA Life Sciences on Tuesday, researchers from the Institut Pasteur of Shanghai under the Chinese Academy of Sciences and other Chinese research institutes compared the genome sequences of the 2019-nCoV to coronaviruses known to infect humans: SARS-CoV and Middle East Respiratory Syndrome (MERS)-CoV.
They found the 2019-nCoV is about 70 per cent similar to the SARS-CoV and 40 percent similar to the MERS-CoV. Analysis showed the 2019-nCoV belongs to the Betacoronavirus group of enveloped, single-stranded RNA viruses that infect wild animals, herds and humans, resulting in occasional outbreaks and infections without apparent symptoms.
In the evolutionary tree, the 2019-nCoV is quite close to the groups of SARS and SARS-like coronaviruses, with the bat coronavirus HKU9-1 as the immediate outgroup.
It is likely these coronaviruses share a common ancestor resembling the bat coronavirus HKU9-1.
Bats being the native host of the 2019-nCoV "would be the logical and convenient reasoning, though it remains likely intermediate host(s) were in the transmission cascade from bats to humans," said researchers.
They noted there is a considerable genetic distance between the 2019-nCoV and the human-infecting SARS-CoV, and even greater distance from MERS-CoV. The genetic analysis raised another question: does the 2019-nCoV adopt the same mechanisms as the SARS-CoV or MERS-CoV used for transmission across species and humans. Or does it have its own?
In the SARS-CoV, spike protein (S-protein) is essential for the virus to attach to the host cell receptor. The researchers evaluated the 2019-nCoV S-protein's ability to interact with human cell receptors. They found that although the binding between the 2019-nCoV and the human cell receptor is weaker than SARS-CoV, it is still considered to be a strong one. The researchers noted that the 2019-nCoV S-protein supports strong interaction with human cell receptors, posing a significant public health risk for human transmission.
China's National Health Commission confirmed 571 cases and 17 deaths at the end of Jan 22. By January 25, this number has risen to 1,287 cases and 41 deaths.
Thailand reported four cases; France three; and South Korea, Japan, Taiwan and the United States one each. Patients in these cases were either residents of Wuhan or recent visitors to the city. Australia on Saturday confirmed its first case of the new coronavirus. The sick man arrived in Melbourne from China a week ago from the Chinese city of Wuhan.
Role of bats, snakes in the outbreak
The new strain of coronavirus that emerged in China may have originated in bats or snakes, according to genetic analysis of the virus.
The theories are based on examination of the genome sequence of the virus released by authorities in the wake of the outbreak, with two studies pointing to the likely role of bats in the outbreak.
One study, published Tuesday in the journal Science China Life Sciences, which is sponsored by Beijing's Chinese Academy of Sciences, looked at the relations between the new strain and other viruses.
It found the coronavirus that emerged from China's Wuhan was closely related to a strain that exists in bats.
"Bats being the native host of the Wuhan CoV (coronavirus) would be the logical and convenient reasoning, though it remains likely there was intermediate host(s) in the transmission cascade from bats to humans," the researchers from several institutions in China wrote in the paper.
That study did not speculate about which animal could have been an "intermediate host," but a second study published Wednesday in the Journal of Medical Virology identifies snakes as the possible culprit.
"To search for (a) potential virus reservoir, we have carried out a comprehensive sequence analysis and comparison. Results from our analysis suggest that snake is the most probable wildlife animal reservoir," the paper says.
The researchers caution that their conclusions require "further validation by experimental studies in animal models".
Neither study explained how the virus may have been transmitted from animals to humans.
But they could offer clues to Chinese authorities as they hunt for the source of the outbreak that has sickened hundreds of people in the country and has been confirmed as far afield as the United States.
Craze for exotic meat
The food market where the deadly virus surfaced offered a range of exotic wildlife for sale, including live foxes, crocodiles, wolf puppies, giant salamanders, snakes, rats, peacocks, porcupines, camel meat and other game.
Gao Fu, director of the Chinese centre for disease control and prevention, said in Beijing on Wednesday that authorities believe the virus likely came from "wild animals at the seafood market" though the exact source remains undetermined.
Severe Acute Respiratory Syndrome, or SARS, was linked to Chinese consumption of civet meat.
Many exotic species are still widely consumed in China or other Asian countries where they are considered a delicacy - like the civet or some rats or bats - or for purported health benefits unproven by science.
The virus is spreading fast
In a report on Wednesday, Imperial College London said it estimated a total of 4,000 cases of the coronavirus in Wuhan alone as of Jan. 18, an infection rate based on the number of cases reported in China and elsewhere.
During a visit to Wuhan, Vice Premier Sun Chunlan said authorities needed to be open about the spread of the virus and efforts to contain it, the official Xinhua news agency said on Thursday, comments likely to reassure global health experts.
The World Health Organization (WHO) has said it will decide on Thursday whether to declare the outbreak a global health emergency, which would step up the international response.
If it does so, it will be the sixth international public health emergency to be declared in the last decade.
Some experts believe the new virus is not as dangerous as previous coronaviruses such as SARS and Middle East Respiratory Syndrome (MERS), which has killed more than 700 people since 2012.
"The early evidence at this stage would suggest it's not as severe a disease as SARS or MERS," Australia's Chief Medical Officer Brendan Murphy told reporters on Thursday.
WHO Director-General Tedros Adhanom Ghebreyesus told reporters in Geneva that China's actions so far were "very strong" but called on Beijing to take "more and significant measures to limit or minimise the international spread".
He added, "We stressed to them that by having a strong action not only they will control the outbreak in their country but they will also minimise the chances of this outbreak spreading internationally. So they recognise that." Despite China's response, stock markets across Asia were on the back foot on Thursday over the virus, led by drops of roughly 1.5 per cent in Hong Kong and Shanghai while China's yuan fell to a two-week low.