Searching for the origin of viruses, including the novel coronavirus now ravaging the world, is an extremely difficult and complicated undertaking prone to many uncertainties. But according to experts, one thing is for sure -- the quest should be underpinned by scientific evidence, rather than politically motivated speculation. 

"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 the Peking University's School of Health Humanities. 

"Hunting down a virus' origin, 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 the patient zero (the first infected case of an epidemic) for HIV/AIDS, but the question remains contentious to this day.

Likewise, scientists are still confounded by the origin of the Ebola virus that first emerged in the 1970s, as well as the influenza virus that has affected humans for over a century, Su added. 

Zhao Guoping, a Chinese molecular biologist and an academician with the Chinese Academy of Sciences, said that searching for a virus's origin 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 field of pathology, clinical medicine and epidemiology, which reflects real-world situations but could be inaccurate due to human interference. 

The other type of evidence entails results of genome sequencing or antibody testing. Zhao said they are 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," he 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 the patient zero for COVID-19, as well as other early infections, might be asymptomatic and leave no medical records behind. He had called on global researchers to proactively search for early cases around the world. 

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

But according to the report of an origin-tracing mission that was 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 a virus's origin 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 should be blamed for the virus's jump to humans. 

"Finding a virus's origin 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 on the issue," Su said, referring to a previous decision by Joe Biden's administration.

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

"Tracing the origin of a virus means studying a highly accidental and rare event, and we should adopt scientific methods, logic and thinking, and devote great efforts to overcome difficulties," he said. 

"For us Chinese scientists, we will continue our research into the virus's origin, based on any available knowledge, skills and methodology," he said.