After a month-long investigation, WHO researchers still think the coronavirus originated in bats.
The WHO's report said that the coronavirus may have jumped from animals to people at wildlife farms.
The most likely intermediary species include minks and pangolins.
After a month-long investigation in Wuhan, the World Health Organization has offered its best guess as to where the coronavirus came from and how it got into the human population.
A 120-page report released Tuesday lists the virus' potential origin scenarios in order of their likelihood. At the top is the possibility that the coronavirus jumped from bats to people via an intermediary animal host. But the WHO team, which visited Wuhan from January to February, was in the end unable to pinpoint which population of bats, or which intermediary species, was carrying the virus.
The group did, however, determine that the cross-species hop most likely happened at a farm where wild animals were bred for food in southern China.
"They take exotic animals, like civets, porcupines, pangolins, raccoon dogs, and bamboo rats, and they breed them in captivity," Peter Daszak, a disease ecologist and member of the WHO team, told NPR.
The WHO team thinks that spillover event, as its known, happened in November or even October 2019. China shut down these types of wildlife farms in February 2020, Daszak said.
'There is a pathway that this virus could've taken'
Daszak said his team found evidence that wildlife farms in China's Yunnan province and surrounding provinces supplied vendors at the Huanan Seafood Wholesale Market in Wuhan. The first cluster of COVID-19 cases reported in December was linked to that market, which sold live animals and frozen meat.
Two studies published last year found that the new coronavirus shares 96% and 97.1% of its genetic code with coronaviruses seen in Chinese horseshoe bat populations from the Yunnan province, which borders Laos, Myanmar, and Vietnam.
"Animals that we know are coronavirus reservoirs or able to carry coronaviruses came from places where the nearest related viruses are found," Daszak said Tuesday in a WHO press conference. "There is a pathway that this virus could've taken to move 800 to 1,000 miles from the rural parts of south China, southeast Asia, to this market."
According to the WHO report, possible intermediary host species that may have been raised at these wildlife farms include: minks, pangolins, rabbits, raccoon dogs, and domesticated cats. All of these species can be infected by the new coronavirus. The team is also considering civets, ferret badgers, and weasels as potential hosts, since these animals got infected with the SARS coronavirus and passed it to people in 2002.
Any contact with an infected animal, or with animal products or poop, can allow a virus to jump from animals to people.
But the WHO team didn't find any infected animals
Daszak's group took 900 samples from the Huanan market, which closed in early January 2020. They swabbed surfaces, examined animal carcasses, and tested sewage, looking for evidence of the virus. The results showed the surfaces were indeed contaminated with viral particles, but none of the animal carcasses studied - or live animals brought to the site - tested positive.
This suggests that humans, not animals, most likely brought the virus into the market. Indeed, the WHO team concluded the virus had been circulating in Wuhan for a month or more before the outbreak there.
The WHO team also examined more than 80,000 samples from cattle, sheep, chickens, ducks, geese, and pigs from 31 provinces across China. There wasn't a single positive case among them. None of the animals had coronavirus-specific antibodies, either, which would have indicated a past infection.
The researchers weren't able to test animals at wildlife in farms from southern China for evidence of infection, however, so they recommended doing so in a follow-up investigation.
Finding the bat population that first harbored the virus may be easier
According to Fabian Leendertz, a wildlife veterinarian with the WHO team, it's more likely that the team will find the bat population the virus first lived in, rather than the animal that passed it to humans.
"At this point, it may well have disappeared from any intermediate host, so sampling bats, in particular, is probably the most likely to yield results," Leendertz told Science.
Bats are common virus hosts: Cross-species hops from bat populations also led to the outbreaks of Ebola, SARS, and the Nipah virus.
Still, the WHO team tested samples from more than 1,100 bats in the Hubei province, where Wuhan is located, and did not see any viruses closely related to the new coronavirus. That non-finding lends credence to the idea that the virus first jumped to people elsewhere in China.
Daszak is still confident, however, that scientists will eventually find the population of bats that were the coronavirus' original hosts.
"It would've been incredible to have a bat with the exact same lineage of viruses," he said. "We didn't see that yet. That will come in the future I think."
Read the original article on Business Insider