Searching for the origin of viruses, including the novel coronavirus, is an extremely difficult and complicated undertaking prone to uncertainties, but one thing that's certain is that the quest should be underpinned by scientific evidence, not politically motivated speculation, experts said.

"Whenever a major infectious disease breaks out, one of the first questions raised by scientists and the public is: Where did it come from?" said Su Jingjing, a professor at Peking University's School of Health Humanities.

"Hunting down the origin of a virus, understanding how it is introduced into the human population and how it spreads further will enable medical and public health experts to better cope with the disease and prevent future outbreaks," she added.

However, Su said, tracing the source of a virus requires large amounts of on-site investigations, thorough laboratory testing and "a great deal of luck".

For instance, she said, it took nearly two decades for global scientists to come to an initial conclusion on who might be "patient zero" (the first case in an epidemic) of HIV/AIDS, and the question remains contentious to this day.

Likewise, scientists remain unable to determine the origin of the Ebola virus, which first emerged in the 1970s, as well as the influenza virus, which has affected humans for over a century, Su added.

Zhao Guoping, a Chinese molecular biologist and an academician in the Chinese Academy of Sciences, said that searching for the origin of a virus must be based on clear and conclusive evidence, but the collection and analysis process poses severe challenges.

He said one type of evidence comes from the fields of etiology, clinical medicine and epidemiology, which reflects real-world situations, but could be inaccurate due to human interference.

The other type of evidence involves the results of genome sequencing or antibody testing. Zhao said this is more definitive, but it is challenging to "establish their connections" to other pieces of proof.

"The origin-tracing task contains a number of uncontrollable factors. Some key information could be lost forever, which means that it will be impossible for us to build a complete chain of evidence," Zhao said during an interview with Science and Technology Daily.

"Sometimes, we might not be able to get to the bottom of the question even after very long periods of research, and we can only make inferences based on available information," he said. "The public should have a rational expectation."

SARS-CoV-2, the virus that causes the COVID-19 disease, has so far presented formidable obstacles to scientists struggling to pin down its origin.

Liu Peipei, a virologist at the Chinese Center for Disease Control and Prevention, said during an earlier briefing that "patient zero" of COVID-19, as well as other of the earliest infections, might have been asymptomatic and there may be no medical records related to that person. Liu had called on global researchers to proactively search for early cases around the world.

In terms of genome sequencing, a widely recognized breakthrough is the discovery of RaTG13, a coronavirus found in horseshoe bats and whose genetic makeup is 96 percent identical to that of SARS-CoV-2.

But according to the report of an origin-tracing mission organized by the World Health Organization and conducted jointly by Chinese and WHO experts in China earlier this year, coronaviruses detected in bats and pangolins are not similar enough to make them the progenitor of the virus.

The report said more efforts are needed to take and test samples from wild animals in Southeast Asia and around the world, where surveys to identify coronaviruses related to SARS-CoV-2 are insufficient.

Su, from Peking University, said collecting samples from bats is a time-consuming procedure, and rigorous precautions must be taken to prevent infections.

"There are previous reports on finding coronaviruses related to SARS-CoV-2 in Thailand, Japan and other parts of Asia," she said. "The workload is comparable to finding a needle in a haystack."

Experts have warned that politicizing the origin of the virus will add more difficulties to an already herculean task as some Western governments have attempted to revive a false accusation that a laboratory incident in China was responsible for the virus jumping to humans.

Politicization opposed

"Finding the origins of a virus should be based on science, logic and rational thinking, and it is scientists who should spearhead the work, rather than politicians or intelligence agencies," Su stressed.

"Involving intelligence agencies in the process is a blatant move to politicize the issue and will only serve to hamper international cooperation," Su said, referring to an earlier decision by the US government.

Liang Wannian, a public health professor at Tsinghua University and head of the Chinese experts on the WHO-convened origin-tracing team, said during an earlier interview that politicization of the issue and the distortion of the team's findings display a disrespect for the scientists' endeavors and will hinder the global fight against the disease.