A new human coronavirus has appeared in China

BEFORE 2003 few outside the field of respiratory medicine would have heard the term “coronavirus”. Then came SARS—severe acute respiratory syndrome—and suddenly the word became familiar. SARS caused a medical panic. It was an unknown illness with a mortality rate of about 10% and there was a brief period when, having escaped from China, where it first appeared, and surfaced in places as far distant as Canada, it seemed to have the potential to cause a global epidemic.

Thankfully, SARS was contained, and now seems to have disappeared in the wild. But the bogeyman status of coronaviruses has not diminished. Hence the mini-panic when a new one began infecting people in Wuhan, the capital of Hubei province, in China. As The Economist went to press 42 patients had been confirmed as being ill with the new virus, one of whom had died.

The virus’s symptoms of fever and pneumonia are similar to those of several other infections, so it was not clear to start with what was happening. The person now believed to have been the first patient developed symptoms on December 8th. The most recent case in China presented on January 2nd. On January 8th, however, a Chinese visitor arriving in Thailand from Wuhan was also found to be feverish, and on January 13th her illness was confirmed as being caused by the new virus.

Once China’s health authorities realised what was going on, they acted fast. On January 1st they shut down a market that seemed to be a common factor between the patients. By January 7th they had isolated the new pathogen, showing that it was a coronavirus. And on January 12th they published the new virus’s genetic sequence, enabling doctors in other countries to check for possible cases.

Coronaviruses, so called because they vaguely resemble monarchical crowns when examined under an electron microscope, are a widespread group that infect many species of mammal and bird. The two human examples known of before 2003 both cause colds, but are not regarded as life-threatening. A diligent search after the emergence of SARS discovered two others that had been circulating, previously unnoticed, in the human population. Then, in 2012, a sixth human coronavirus was discovered and shown to be responsible for newly described symptoms now called Middle East respiratory syndrome (MERS) that kill about a third of those infected. The agent responsible for the outbreak in Wuhan, which has yet to be named formally, appears to be the seventh.

What is not yet clear is whether the Wuhan virus can, like the other six, spread directly from person to person. Novel human viruses are usually pathogens established in another animal that have jumped the species barrier. To be successful, though, they must also have mutated sufficiently to pass between members of their new host. The virus responsible for SARS, for example, came from bats, via civets, before infecting people. That responsible for MERS came from camels. Which species harboured the Wuhan virus remains unknown. The initial suspicion—hope, almost—was that each of those infected picked the virus up independently from whichever animal reservoir harbours it, rather than from another human being. The now-closed market being a common factor in infections has encouraged this belief, as has the failure of China’s health authorities to find signs of infection in those who had been in contact with patients.

Given the lack of new cases, it looks possible that even if person-to-person transmission has happened, the swift response to the new infection has nipped things in the bud. That is encouraging, as is the fact that the traveller to Thailand was detected by equipment installed for the purpose at Bangkok airport. This picked up her elevated body temperature and alerted the authorities. In a world where a virus could be halfway around the planet before medical science has got its boots on, that is something to be grateful for.■