TOKYO -- The coronavirus epidemic is the most threatening disease crisis to emerge from China since the outbreak of severe acute respiratory syndrome, or SARS, in 2002. Like SARS, it threatens to spread to many countries: "This epidemic represents a clear and ongoing global health threat," says one study.
Since Dec. 1, when the first person is believed to have contracted the disease in Wuhan, scientists and doctors have been racing to find out how it spreads, how dangerous it is, and how it can be contained. Some aspects of the coronavirus are very worrying, but others offer a degree of reassurance.
What is it?
Like SARS, it is a coronavirus, a type of virus that can affect humans and other mammals, causing flu-like symptoms. Most coronaviruses -- so called because of the spikes that resemble a crown -- have mild symptoms, but there are fears that even more dangerous viruses may cross from animals.
The virus was first thought to have originated in a Hunan seafood market in Wuhan, a city of 11 million people, and perhaps to have spread from snakes. But scientists now believe that it spread into the market rather than having originated there. Still, there is no clear answer regarding its true source.
How dangerous is it?
The virus can be very dangerous, especially to men, older people of both sexes, and those with existing health conditions. In severe cases, it causes labored breathing and respiratory distress, with severely ill patients being admitted to intensive care units and treated for pneumonia and organ damage.
The death rate is not yet clear, although it appears to be in line with SARS at about 10%. A study by doctors of 41 patients in Wuhan, published in Lancet, found that about a third had developed acute respiratory distress, 13 were admitted to intensive care, and six died.
After SARS broke out in Guangdong, China in November 2002, it infected 8,000 people in a year and led to 774 deaths in 29 countries, with most fatalities in China and Hong Kong, according to a study by the World Health Organization.
Middle East respiratory syndrome, a coronavirus epidemic in 2012, did not spread as fast but was more deadly, killing 37% of patients.
The Wuhan coronavirus is not always dangerous. Some patients show only mild to moderate symptoms. Doctors even found a 10-year-old child in Shenzhen who had no symptoms. Seasonal flu can itself be dangerous, with one study putting the annual global death toll from the illness at between 290,000 and 650,000.
How do you catch it?
The coronavirus appears to spread like influenza, mainly by patients sneezing and coughing, which expel droplets into the air. It may also be contracted by touching surfaces on which the virus is deposited. That some hospital staff have been infected is a worrying sign of its capacity to spread.
How fast is it spreading?
The crucial factor in determining whether a new virus turns into an epidemic or pandemic is how many others each patient infects. If it is less than one other person, then risk is limited. The new coronavirus seems to spread quite easily, although not as rapidly as measles.
One study published by Imperial College in the U.K. estimated that the coronavirus has a transmission rate of 2.6, which is about the same as SARS. Another U.K. study published by Lancaster University put the transmission rate at between 3.6 and 4, based on the spread in China.
According to Japan's National Institute of Infectious Diseases, a measles patient can infect 12 to 18 people, while flu only spreads to between two and three. The higher the rate, the more urgent it is to limit the spread by identifying and isolating patients quickly, as China is trying to do.
Can it be contained?
Short of medical treatment or vaccination, the only way to contain an epidemic is to stop it from spreading. According to the Lancaster study, there could be 190,000 cases in Wuhan by February 4. More than 70% of transmissions would need to be halted to curb the epidemic.
China has taken extraordinary measures to stop patients passing on the virus, including a travel ban in Wuhan. The difficulty now, compared to when SARS appeared, is that more Chinese people travel abroad, leading to the virus possibly spreading to far more countries.
One uncertainty is whether the virus is easily passed to others before symptoms emerge. That would increase the threat, since it would be much harder to identify those who are spreading it. The incubation period is between two and 10 days before symptoms emerge.
Can it be treated?
There are no antiviral treatments for the virus, although there are hopes of being able to develop drugs to limit its effects, if not cure the illness outright. Antiviral drugs and steroids were used later on SARS patients.
Under one initiative, the Coalition for Epidemic Preparedness Innovations this week began a series of three programs to develop a vaccine.