A World Health Organization mission to China to investigate the origins of Covid-19 has ended without a clear answer, but research further afield could help fill in some of the gaps, according to members of the WHO team.
The 14-person international team of specialists and officials concluded on Tuesday that it was most likely that the pandemic virus jumped to people via an intermediary animal, and "extremely unlikely" that it was the result of a laboratory leak.
At their press conference in Wuhan on Tuesday, the team did not report finding any patients earlier than previously known or any infected animals.
Team lead and WHO food safety scientist Peter Ben Embarek said much work remained to be done, both in and outside China.
That included testing samples from blood banks in places with reports of potential cases in 2019, hunting for viruses in bats across Southeast Asia, and getting a better understanding of whether frozen products played any role in the introduction of the virus.
"The possible path from whatever original animal species all the way through to the Huanan market could have taken a very long and convoluted path involving movements across borders, travels, etc," Ben Embarek said in Wuhan, wrapping up the mission.
During the long-awaited trip to Wuhan, the team spent nearly a month trying to understand how the virus that causes Covid-19 could have jumped from bats - where it is thought to have originated - to humans.
Team member David Hayman, who joined the mission remotely on behalf of the World Organisation for Animal Health (OIE), told the South China Morning Post that he "expects there to be a plan for future sampling and testing of animals", in China and elsewhere.
Hayman, who is co-director of the OIE Collaborating Centre in Veterinary Epidemiology and Public Health at Massey University in New Zealand, said there were several ways to search for animals that might have played a role, including using Wuhan "as a centre" to work backwards to find as many farms and other sources of animals for the city as possible.
The other would be a "probability-based sampling approach", where researchers carried out targeted testing of suspected animal hosts.
Another team member, disease ecologist Peter Daszak of EcoHealth Alliance in the United States, said Southeast Asia was a key region of interest for further research into animals involved in the virus' spread.
"We know that there is very little surveillance on the other side in the whole region of Southeast Asia," he told the BBC in Wuhan on Tuesday.
Such work is already under way, with two separate groups of researchers - one in Thailand and another in Cambodia - releasing findings of closely related coronaviruses in bats over the past month.
The WHO has not specified the next steps it will take next in the search for the origins, but a document laying out the "China part" of the origins-tracing work written in July pointed to a "phase 2" that could include international studies.
There were a "range of possibilities" for how the WHO might proceed but such steps might not have been decided, according to global health security expert Adam Kamradt-Scott of the University of Sydney.
One possibility, depending on evidence, is to take a closer look at medical reports indicating the virus might have been present in Europe before it was identified in Wuhan.
"If the focus shifts to the European context, it may be that they (the WHO) send a delegation to speak with officials in a country," he said.
Chinese officials have long said the research into the origins of the virus might need to take place overseas. Beijing has maintained that just because the virus was identified in China does not mean that is where it emerged.
Chinese National Health Commission spokesman Mi Feng said on Tuesday that the China part of the WHO mission had "concluded".
The international team has not released its final report but has already met resistance from the United States, with a State Department official saying on Tuesday that the US would not accept the WHO team's findings without independently verifying them, citing concerns about transparency.
Dutch virologist Marion Koopmans, one of the members of the WHO team, responded, saying on Twitter: "And so it starts. No need to wait for the report, right?"
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