THE deadly new coronavirus has killed more than 100 people – with the number of infections almost doubling in a day to more than 4,500.
A growing number of countries around the world have reported cases as governments scramble to control the spread.
Experts in China said tests proved humans first caught the bug from animals sold at a seafood market in Wuhan.
Scientists are concerned because it is closely related to other diseases including SARS, which killed nearly 800 people between 2002 and 2003.
But how does the new illness, dubbed 2019-nCoV, compare?
The new coronavirus
Coronaviruses are a large family of viruses that can cause infections ranging from the common cold to Severe Acute Respiratory Syndrome (SARS).
The virus has a wide range of symptoms, including fever, coughing, shortness of breath and breathing difficulties.
Severe cases can cause pneumonia, severe acute respiratory syndrome, kidney failure and death.
Experts are still working to understand more about the new form, which emerged at the end of December, but believe that it jumped from animals to humans.
Like the viruses that cause SARS and Middle East Respiratory Syndrome (MERS), the new one is an RNA virus – with RNA as its genetic material, rather than DNA.
That means the virus blends with its host’s DNA, and can mutate rapidly.
Where did coronavirus start? From bats to snakes – the theories on deadly virus’ origins
The killer coronavirus was spread from bats to snakes to humans, experts have claimed.
An outbreak of the virus is understood to have started at an open air fish market in the Chinese city of Wuhan – which has since been put in lockdown after 25 people died and more than 600 people were infected globally.
A new study published in the China Science Bulletin this week claimed that the new coronavirus shared a strain of virus found in bats.
Previous deadly outbreaks of SARS and Ebola were also believed to have originated in the flying mammal.
Experts had thought the new virus wasn’t capable of causing an epidemic as serious as those outbreaks because its genes were different.
But this latest research appeared to prove otherwise – as scientists scrabble to produce a vaccine.
In a statement, the researchers said: “The Wuhan coronavirus’ natural host could be bats … but between bats and humans there may be an unknown intermediate.”
Meanwhile, scientists at Peking University also claim that the deadly virus was passed to humans from bats – but say it was through a mutation in snakes.
The researchers said that the new strain is made up of a combination of one that affects bats and another unknown coronavirus.
They believe that combined genetic material from both bats and this unknown strain picked up a protein that allows viruses bind to certain host cells – including those of humans.
After analysing the genes of the strains the team found that snakes were susceptible to the most similar version of the coronavirus.
It meant that they likely provided a “reservoir” for the viral strain to grow stronger and replicate.
Snakes are sold at the Huanan Seafood Market in central Wuhan and may have jumped to other animals before passing to humans, they claim.
But a senior researcher at the Wuhan Institute of Virology, who asked not to be named, said the findings should be treated with caution.
He told the South China Morning Post: “It is based on calculation by a computer model.
“Whether it will match what happens in real life is inconclusive.
“The binding protein is important, but it is just one of the many things under investigation. There may be other proteins involved.”
The expert believes that the new strain was an RNA virus, meaning that its mutation speed was 100 times faster than that of a DNA virus such as smallpox.
It can be transmitted from person to person through coughing and sneezing, which increases the risk of it being passed on.
Chinese health authorities also said it can spread before symptoms show up and its incubation period can range from one to 14 days.
So far, the new coronavirus doesn’t seem to spread as easily among people as SARS or influenza.
Most of the cases so far that spread between people were of family members and health workers who had contact with patients.
That suggests the new virus isn’t well adapted to infect people.
The World Health Organisation called the outbreak an emergency for China, but stopped short of designating it a global emergency.
Cases have been reported in Hong Kong, Macau, Taiwan, Thailand and the United States, as well as Australia, Canada, France, Japan, Malaysia, Nepal, Singapore, South Korea and Vietnam.
So far, no deaths have been reported outside China.
Death toll: 106
Severe acute respiratory syndrome (SARS) first appeared during a pandemic in China in 2002.
Like the current outbreak, it’s caused by a coronavirus and displayed similar flu-like symptoms such as a fever, cough and breathing difficulties.
It can also result in a highly contagious and potentially life-threatening form of pneumonia.
SARS is an airborne virus which is spread in small droplets of saliva coughed or sneezed into the air by an infected person.
It can also be spread indirectly via surfaces and even through poo if an infected person doesn’t wash their hands properly.
Evidence from the SARS pandemic of 2002 to 2003 showed people living with or caring for someone with a known SARS infection were most at risk of developing the infection themselves.
It’s thought that a strain of the coronavirus usually only found in small mammals mutated, enabling it to infect humans.
The SARS infection quickly spread from China to other Asian countries and there were also a small number of cases in several other countries, including 4 in the UK.
It was eventually brought under control in July 2003, when people suspected of having the condition were isolated and passengers travelling by air were screened.
In 2004 there was another smaller SARS outbreak linked to a medical laboratory in China.
It was thought to have been the result of someone coming into direct contact with a sample of the SARS virus, rather than being caused by animal-to-human or human-to-human transmission.
There’s currently no cure for SARS, but research to find a vaccine is ongoing.
Death toll: 774
The 1918 Spanish flu pandemic was the deadliest outbreak of the virus in history killing the most people in the shortest timeframe.
It was first observed in Europe, the US and parts of Asia before it quickly spread throughout the world.
The spread was aided by modern ships and a world war that required moving huge armies quickly across the globe.
It was wrongly named the Spanish flu because it was first reported by a newspaper in Madrid, but it’s now believed to have started in Kansas, US.
The virus caused typical flu symptoms, including fever, nausea, aches and diarrohea but many developed severe pneumonia, which ultimately became fatal.
Dark spots would appear on the cheeks and patients would turn blue, suffocating from a lack of oxygen as lungs filled with a frothy, bloody substance, NPR reports.
Research reconstructing the virus suggested it began in birds, then rapidly mutated, leaping to humans.
Unlike the typical flu, where the highest mortality is in infants and the elderly, the 1918 flu also struck down young, healthy adults.
The military, with its overcrowded camps and troops ships, took a particularly bad hit.
In 2014, scientists revealed that they had solved the mystery of how the Spanish started and why it became so deadly.
A study by the Proceedings of the National Academy of Sciences found that people born after 1889 had not been exposed to the kind of virus which devastated the world in 1918.
This explains why the deadly pandemic largely targeted young adults while older patients, who had built up some immunity, would often make a full recovery.
Also a sudden movement of avian flu genes at the time– causing a change in the kind of hemagglutinin in an already existent flu strain – likely led to the pandemic.
Hemagglutinin is a kind of protein which binds the virus to cells.
There was also no vaccine for the strain in 1918.
Experts say that most people living today would have some immunity to viruses in the 1918 virus’ family, called H1N1, while modern antiviral drugs may also be effective.
Death toll: 20-50 million (estimate)
Infections: 500 million (estimate)
Ebola virus disease is a serious viral infection that originated in sub-Saharan Africa.
It was first detected in 1976 in an outbreak near the Ebola River in what is now the Democratic Republic of Congo.
The virus is thought to have originated in fruit bats, which are considered a delicacy in the area where the outbreak started.
A person infected with Ebola will typically develop a high temperature, a headache, joint and muscle pain, a sore throat and severe muscle weakness.
Symptoms start suddenly – between two and 21 days after becoming infected.
Diarrhoea, being sick, a rash, stomach pain and reduced kidney and liver function can follow.
The infection may then cause internal bleeding as well as bleeding from the ears, eyes, nose or mouth.
Unlike the new coronavirus, Ebola is not an airborne disease, and as such it is impossible for a person to become infected by inhaling the same air as a patient.
People can become infected through direct contact with bodily fluids of someone with the virus.
Those at highest risk are typically healthcare workers, family members of those infected and other people who come into close contact with an infected person.
Sexual transmission can occur, from men to women or men, after a person’s symptoms have disappeared and they are declared free from the disease.
No one has caught Ebola from someone else in the UK.
There is no proven cure for the virus but in December 2016, it was reported that a new and effective vaccine had been developed.
The 2014–2016 outbreak in West Africa was the largest Ebola outbreak since the virus was first discovered in 1976 and ended with more than 28,600 cases and 11,325 deaths.
It started in Guinea and then moved across land borders to Sierra Leone and Liberia.
The current 2018-2019 outbreak in eastern DRC is highly complex, with insecurity adversely affecting public health response activities.
Death toll (2014-2016): 11,325
Cases (2014-2016): 28,600