Chinese researchers investigating the animal origin of the coronavirus outbreak in China have said that the endangered pangolin may be the “missing link” between bats and humans.

Bats are known carriers of the latest strain of the disease, which has infected at least 31,000 people and killed more than 630 worldwide, mostly in China where the outbreak started.

A genetic analysis showed that the strain of the virus currently spreading among humans was 96% identical to that found in bats.

But according to Arnaud Fontanet, from France’s Pasteur Institute, the disease did not jump straight from bats to humans. “We think there’s another animal that’s an intermediary,” he told AFP.

The Sars outbreak of 2002-3, involving a different strain of coronavirus, was transferred to humans by the civet, a small mammal whose meat is considered a delicacy in China.

Many animals are capable of transmitting viruses to other species, and nearly all strains of coronavirus contagious to humans originated in wildlife.

Several studies have shown that the bat-borne virus lacks the necessary hardware to latch onto human cell receptors. But it’s still not clear which animal is the missing link.

Fontanet believes the intermediary was “probably a mammal,” possibly belonging to the badger family.

After testing more than 1,000 samples from wild animals, scientists at the South China Agricultural University found that the genome sequences of viruses in pangolins to be 99% identical to those on coronavirus patients, the official Xinhua news agency reported.

But other experts urged caution. “This is not scientific evidence,” said James Wood, head of the department of veterinary medicine at the University of Cambridge. “Investigations into animal reservoirs are extremely important, but results must be then be published for international scrutiny.”

“Simply reporting detection of viral RNA with sequence similarity of more than 99% is not sufficient,” he added.

To conclusively identify the culprit, researchers would need to test each species that was on sale at the market – a near impossibility given that it is now permanently closed.

Martine Peeters, a virologist at France’s Institute for Research and Development (IRD), was part of the team that identified the host animal of the Ebola virus during recent epidemics.

They found that it was indeed a bat that passed the virus on to humans, and Peeters believes that is likely to be the case this time around. During her Ebola research, “we collected thousands of bat dropping from several sites in Africa,” Peeters told AFP.

Fontanet said that the Chinese are carrying out research now.

“They say they’ve analysed samples from a rubbish truck,” he said. “They don’t say which, but I think it’s likely to have been excrement that was just lying around.”

While it may be too late for this outbreak, identifying the carrier animal for the novel coronavirus could prove vital in preventing future flare-ups.

China, for example, outlawed the sale of civet for food during the Sars epidemic.

Eric Leroy, a virologist and vet at the IRD said that the search could well turn up a result quickly, as with Sars. Equally, it could take years. “With Ebola, research started in 1976 and we didn’t see the first results published until 2005,” he told AFP.

One determining factor could be what percentage of the same species are infected. “If that’s low, less than 1% for example, that’s obviously going to lower the chance you stumble upon an infected animal,” said Leroy.

For Fontanet, coronavirus is just the latest example of the potentially disastrous consequence of humans consuming virus-carrying wild animals. He said that China needed to “take pretty radical measures against the sale of wild animals in markets”.

Beijing has prohibited the practice, but only moved to do so last month, when the outbreak was already out of control.

“Each time, we try to put out the fire, and once it’s out we await the next one,” said François Renaud, a researcher at the Paris-based National Centre for Scientific Research.

He recommended compiling a watch list of all animals that could potentially transmit viruses to humans. “You need to see epidemics before they come, and therefore you need to be proactive,” he said.