It is "extremely unlikely" that the novel coronavirus spread to humans from a laboratory leak, a team of international experts from the World Health Organization said on Tuesday, adding that future studies into the origin of the virus will head "wherever indicated" and not be "geographically bound".

No known viruses being identified or researched in laboratories around the world have been found to be highly linked to the novel coronavirus, and the team's fieldwork in Wuhan, Central China's Hubei province, in the past four weeks, as well as its discussion with local scientists, also supported dismissing the theory that a laboratory incidence triggered the outbreak, Peter Ben Embarek, a WHO expert on animal disease and food safety, said during a news conference.

Referring to the Chinese Academy of Sciences' Wuhan Institute of Virology, he said the state of the laboratory shows "it was very unlikely that anything could escape from that place".

Having eliminated the possibility of a laboratory leak, Embarek suggested focusing on rational facts at hand and conducting systematic analysis.

"It is a much more useful approach than to put personal feelings and views or only looking at half the arguments," he said.

Embarek heads a 17-member international expert team convened by the World Health Organisation for origin tracing of the novel coronavirus in Wuhan with Chinese experts from Jan 10 to Tuesday.

Their work in China shows the most likely pathway for the virus's introduction into the human population is through intermediary species, and the possibility of two other routes examined by the team — direct transmission from an animal host to humans and transmission through cold or frozen food — are not ruled out at the moment, according to Embarek.

In the next step, Embarek stressed that research into the virus's origin should not be confined to certain regions.

He said the possible transfer of the virus from animal hosts to the human population "could have taken a long and convoluted path, involving movement and travel across borders before arriving in Huanan market." Some of the earliest cases detected in Wuhan in December 2019 were linked but not confined to the Huanan Seafood Market.

"We need to conduct more surveys into certain animal species that could act as a reservoir, including more sampling and study of the bat population, not only in China, where a lot of bats have already been tested," he said.

"Some of the similar species found in China are also found in neighbouring countries and in other parts of the world," he said, adding that the bat population outside China has not been sufficiently tracked and tested at this stage.

Based on the team's research this far, bats and pangolins have been identified as the most likely candidates to be reservoirs of the virus, but genome sequences of coronaviruses found in them are not similar enough with the virus circulating in the public to ascertain their roles.

Liang Wannian, head of the China team during the international group's study in the country, said potential natural hosts of the virus also include animals highly susceptible to the disease, such as mustelids and felids.

He added that mass testing of animal products from the Huanan seafood market and bat colonies in Hubei province, as well as livestock, poultry and wild animals across the country, have so far not detected traces of the novel coronavirus.

Though environmental samples collected from the Huanan seafood market revealed prevalent contamination with the virus, the team said the market is only one of several places where the virus was found.

"The virus may had made its way into the market by infected personnel, contaminated goods in cold-chain logistics, animal products or other means," he said.

Liang said evidence available indicated that there is unreported circulation elsewhere in Wuhan city outside the market.

To better understand the virus's origin, Marion Koopmans, a virologist and a team member, said more efforts should be devoted to finding and analysing the earlier spread of the virus.

"We should really go and search for evidence for earlier circulation wherever that is indicated," she said.

This article originally appeared on [China Daily][1] and has been reproduced with permission.