SINGAPORE - Viruses that originate in animal hosts before spreading to humans are not new, but scientists have never previously had to contend with the reverse, said infectious diseases expert Wang Linfa on Thursday (Nov 12).
He said one of the more worrying characteristics of the Sars-CoV-2 virus responsible for Covid-19 is that it can spread from humans back to animal hosts - a process known as spillback - and then to humans again.
Speaking on the first day of a two-day virtual Covid-19 seminar on the theme "Dissecting the disease and its effects", Professor Wang said there is no doubt Sars-CoV-2 originated in animals.
"While we have not found a virus identical to Sars-CoV-2 in animals, we know that related viruses can infect bats and pangolins in their natural environment," said Prof Wang, who is the director of the Emerging Infectious Diseases programme at Duke-NUS Medical School.
"But we now have discovered this spillback - humans have given the virus to cats, dogs, tigers, lions and minks."
Prof Wang noted that cases of farmed minks carrying mutated forms of the virus have been detected in The Netherlands and, more recently, Denmark, which triggered mass culling of the animal bred for its fur.
Infected minks have also reportedly passed the virus back to humans.
"This is very scary, but it's not the worst case because we are still dealing with farmed animals. As long as the government has the political will and resources, we can control it by slaughtering or quarantining the animals," Prof Wang said.
What is more worrying, he said, is the possibility of other wildlife becoming hosts for the virus, which will then likely mutate and create new variants.
"From Sars-CoV-2, we will have Sars-CoV-3, 4, 5... and that can spillover to other animals and come back to humans. This is a real threat and we seriously need to think about this."
Nearly a year on since the first case of Covid-19 was reported in the Chinese city of Wuhan, the question of exactly how the pandemic started and where the virus came from has gone unanswered, noted Prof Wang.
The issue has become hotly politicised as tensions between the United States and China intensified in the last few months, but experts seeking the answer must look beyond China, he said.
He cited similar comments from other world experts, including two Britons: Dr Peter Daszak, head of the global health non-profit organisation EcoHealth Alliance and Dr Jeremy Farrar, director of medical research charity Wellcome Trust.
Prof Wang noted the closest genetic relative of the virus responsible for Covid-19 in humans was found in bat hosts in Yunnan province, close to China's southern borders with Myanmar, Laos and Vietnam.
As South-east Asia has a higher genetic diversity of bats than China, scientists have a better chance of finding the origin of Covid-19 outside China, he added.
The webinar was organised by the College of Clinician Scientists, part of the Academy of Medicine, Singapore.
Other experts on the panel included Prof Kishore Mahbubani, a distinguished fellow at the Asia Research Institute in the National University of Singapore; Prof Lisa Ng, a senior principal investigator at the Agency for Science, Technology and Research; and Associate Prof David Lye, director of infectious disease research at the National Centre for Infectious Diseases.
Prof Mahbubani noted that countries that have done better in handling Covid-19 generally prized collective responsibility over individual rights and freedoms.
Countries with a history of "fiscal irresponsibility" have also fared more poorly compared to countries like Singapore which have been "saving for a rainy day" for decades, he added.
He also singled out the US government for its decision to accelerate its geopolitical contest with China during the pandemic. This was a "complete mistake" that went against common sense, he said.
During the seminar, Prof Ng and Prof Lye gave detailed technical overviews of recent scientific research on Covid-19 in Singapore.