How did China's coronavirus outbreak start?

China’s mysterious coronavirus outbreak is inciting global panic, with 17 confirmed deaths so far.

Virtually unheard of a month ago, the new strain has struck more than 500 people both in its “native” China and beyond, reaching the US earlier this week.

READ MORE: Billions of journeys to celebrate Chinese New Year raise fears coronavirus will spread worldwide

Experts fear patient numbers may have reached as high as 9,700 in the city of Wuhan, the capital of Hubei province, where it all began.

The strain triggers flu-like symptoms, including breathlessness and fever. In the most severe cases, victims succumb to pneumonia.

Where did the new coronavirus come from?

Most people will battle a mild coronavirus at some point, with strains of the pathogen being responsible for the common cold.

Coronaviruses can also trigger life-threatening epidemics, like the severe acute respiratory syndrome (Sars) outbreak that killed 774 people across dozens of countries in the early 2000s.

The new coronavirus strain, 2019-nCoV, likely originated at a seafood market in Wuhan.

The market also sold a range of processed and live meat including donkeys, poultry, camels, foxes, badgers, hedgehogs and rats.

Most of those who initially fell ill worked at, or visited, the market.

“[2019-nCoV is] an RNA virus, which mutate all the time,” Professor Neil Ferguson, from Imperial College London, said.

In simple terms, RNA is a “precursor” to the more well known DNA.

Constantly-evolving viruses can develop the ability to “jump” to new species.

This was the case with bird flu, which “occurs naturally among wild aquatic birds, and can infect domestic poultry, and other bird and animal species”, according to the Centers for Disease Control and Prevention (CDC).

Scientists from Peking University in Beijing have traced 2019-nCoV to snakes, namely the Chinese krait and cobra.

They compared the DNA of the virus to that of other pathogens from various places and species.

Results suggest 2019-nCoV is a “combination of a coronavirus found in bats and another coronavirus of unknown origin”.

The virus is thought to contain a mix of proteins that bind to cell receptors, allowing it to enter and trigger disease.

The team then found snakes were likely the “intermediate host” between bats and humans, with the mix of proteins facilitating the species “jump”.

Snakes often hunt bats in the wild and were reportedly sold at the Wuhan market, according to The Conversation.

How the virus could survive in both a cold and warm-blooded species is unclear.

Not all experts are convinced, however.

“It is still not known with certainty and it may never be definitively proved,” Professor Paul Hunter, from the University of East Anglia, said.

“There are initial, although contested, reports the virus has already been detected in both bats and snakes, and the strains in both bats and snakes are similar to each other, and to the strains from human cases.

“There is still much more to find out about the virus and there is a real possibility the exact origin may not be found.

“The big question is no longer where it came from, but how and where it is spreading in human populations.”

As well as Sars, Middle East respiratory syndrome (Mers) is another coronavirus strain.

This kills about three or four in every 10 patients, according to the Centers for Disease Control and Prevention.

Sars and Mers are both thought to have originated in bats.

The masked palm civet, a mammal native to the Indian subcontinent and south-east Asia, was an intermediate host for Sars between bats and humans.

Camels played the intermediate host for Mers.

The lack of “genetic diversity” in viral samples from different patients suggests 2019-nCoV “jumped” from animals to humans as recently as last month.

The Wuhan market, which was shut at the beginning of the year, “conducted illegal transactions of wild animals”, the BBC reported.

Dr Ben Cowling, from the University of Hong Kong, claims tracing other cases to the market could help identify the animal behind the outbreak.

Containers and cages could also be tested for the virus’ DNA, he added.

Yet, disinfection of the area makes the virus difficult to trace, The Conversation reported.

“We don’t know the animal source,” Professor Ferguson said.

“Live animal markets are a risk, whereas we buy packaged meat from the supermarket.”

What is the new coronavirus?

Like other coronavirus strains, 2019-nCoV typically starts with flu-like symptoms, including fever, cough, shortness of breath and breathing difficulties.

Six coronaviruses are known to infect people, with 2019-nCoV being the “seventh”.

In rare cases, coronaviruses can lead to lower-respiratory tract infections, such as pneumonia or bronchitis.

These tend to occur in babies, the elderly or those with weak immune systems.

2019-nCoV fatalities are occurring as a result of pneumonia.

This comes about when a respiratory infection causes the alveoli (air sacs) in the lungs to become inflamed and filled with fluid or pus, according to the American Lung Association.

The lungs then struggle to draw in air, resulting in reduced oxygen in the bloodstream.

“Without treatment the end is inevitable,” the charity Medecins San Frontiers reported.

“Deaths occurs because of asphyxiation.”

China's National Health Commission confirmed on Monday it can be passed from person-to-person, like other coronaviruses.

These commonly spread via coughing, sneezing, shaking hands or touching a contaminated object.

The virus enters the body if contaminated hands touch the eyes, nose or mouth.

In rare cases, faecal contamination can be to blame.

There is no specific treatment for coronaviruses, according to the CDC.

If the infection triggers pneumonia, doctors work to combat the complication.

When a virus is to blame - like with 2019-nCoV - pneumonia must be treated via “antiviral medication”, according to the American Lung Association.

US health officials are working on a vaccine against 2019-nCoV, however, it will likely be months before the first stage of trials are underway and more than a year before it is available to the public, CNN reported.

For now, the World Health Organization advises people avoid “unprotected” contact with live animals, thoroughly cook meat and eggs, and stay away from those with flu-like symptoms.