• Video report by ITV News Video Producer Natalia Jorquera

The coronavirus outbreak has been declared a global public health emergency by the World Health Organisation, but how was the deadly disease born?

The current outbreak of the coronavirus was first reported in Wuhan in late December, and it has now spread to 18 countries outside of China.

In China, the death toll from the coronavirus has risen toe more than 300 and the number of confirmed cases of infection has increased to more than 14,000.

Meanwhile dozens of UK nationals have been flown home from Wuhan and on Sunday another eleven will join the 83 already in 14-day quarantine.

The first cases of coronavirus have been reported in the UK, with two people testing positive and the pair are being treated at a specialist unit in Newcastle.

The latest coronavirus outbreak has killed 259 people. Credit: AP
  • How is a new virus born?

Coronavirus is a zoonotic virus, which means it is a disease that spreads from one species to another, however it is unclear which species is the culprit of the latest outbreak.

A zoonotic virus is born is when a single animal is infected with two related viruses.

Professor Ian Goodfellow, department of pathology, University of Cambridge: "My best guess is that it came from wild or domestic animals that were being kept at the Wuhan food market, including the civet cat.

"Now the civet cat is in fact the animal which the SARS coronavirus emerged from several years ago."

Sars - severe acute respiratory syndrome - was also a coronavirus and it killed 774 people and infected around 8,100 people in 2003.

The current Wuhan coronavirus outbreak has overtaken the total Sars cases and it is a strand of the virus not seen before.

Experts predict we will see more viruses evolving in the future.

Coronavirus is a zoonotic virus. Credit: Centers for Disease Control and Prevention
  • Where are new diseases likely to emerge?

New diseases are likely to spring up in urban environments, professor of veterinary infectious diseases Eric Fevre, of University of Liverpool, told ITV News.

"Where we as humans have created very densely packed human populations, where alongside us there are bats and rodents and birds, pets and other things living with us," professor Fevre said.

"That creates very intense interaction and opportunities for things to move from species to species."

He added: "There are other such environments, often created as part of the economy or the way we live, e.g slaughterhouses where individuals who work there are in intense contact not just with animals but with the different parts of the insides of animals or wet markets.

"Similarly where animals are sold, cut up and cleaned and where there are a lot of people interacting with those individuals."

New diseases are likely to spread in urban environments. Credit: AP
  • How do you combat new viruses?

Professor Fevre explained the way to combat new viruses is being prepared and doing more routine and regular surveillance at places, which are a breeding ground for these viruses.

"It's very difficult to develop a drug or vaccine for something we don't know about so we always have to start the development process after those events have occurred," he explained.

But typically it takes between four to five years to develop a vaccine for a new virus.

Several groups are working on a vaccine right now, but there is no guarantee it will be ready before the end of the current outbreak.