Future pandemic could stem from coronavirus transmitted from humans back to bat: Expert

Professor Wang Linfa said that most scientists believe that the ancestral strain of the Sars-CoV-2 virus that causes Covid-19 exists in bats found in Asia.
Professor Wang Linfa said that most scientists believe that the ancestral strain of the Sars-CoV-2 virus that causes Covid-19 exists in bats found in Asia.ST PHOTO: LIM YAOHUI

SINGAPORE - A new challenge that countries may possibly face in the future is the emergence of a new Sars-CoV-3 virus arising from humans transmitting the coronavirus back to bats.

Known as reverse-zoonosis, this occurs when infectious viruses are transmitted from humans back to animals, said Professor Wang Linfa from the Duke-NUS Emerging Infectious Diseases programme.

He was speaking about the science behind pandemics and what could lead to a future pandemic at the Special Ministerial Conference for Asean Digital Public Health on Wednesday (Oct 6).

Prof Wang said that most scientists believe that the ancestral strain of the Sars-CoV-2 virus that causes Covid-19 exists in bats found in Asia.

The virus was then transmitted to an "animal X", possibly pangolins or civets, before being transmitted to humans at the Wuhan fish market.

"What followed was massive human transmission... But what surprised us was that this virus could easily go from humans back to animals," said Prof Wang.

There have been a few reports of pets catching the coronavirus from their owners, but no evidence of pet-to-owner transmission has been established.

"It would be worrying if humans can infect novel hosts, like bats in the American continent which are not natural reservoirs for the virus," Prof Wang said.

A possible scenario of this would be an infected human leaving behind a half-eaten fruit, which is picked up by a bat.

This research theory comes on the back of Prof Wang's expertise on bat zoonology and immunology.

Prof Wang was among the team of local researchers who managed to successfully culture the novel virus after it emerged in Wuhan last year, making Singapore the third country outside China to do so. This enabled Singapore to begin manufacturing its own polymerase chain reaction tests to detect the virus.

He was also a member of the emergency committee convened by the World Health Organisation (WHO) in the early stages of the outbreak. The committee advised the WHO on Jan 30 last year that the outbreak constituted a public health emergency of international concern.

"Bats have a very unique immune system in that they can sustain a virus without developing disease. However, the virus can still mutate and transmit to animal X, Y, or Z. So when that mutated virus goes to animal X,Y,Z and gets to a human, then that's where we get our disease X,Y,Z or Sars-CoV-3," said Prof Wang.

Each time a virus jumps between species, it is forced to make major changes because genetically, it has to adapt to its new host.

"When we have more jumping or spear over to other species, the virus will change more. One of these new viruses could then become Sars-Cov-3," he added.

But in reality, how can countries prepare for such a pandemic? Prof Wang suggests three levels of preparedness.

The first would be the pre-emergence stage - looking at what viruses are present in different animals and which animals are the ones that humans trade and consume most frequently.

This is difficult to detect, given that scientists do not have a "crystal ball" to determine if a particular virus circling in animals is ready to jump over to humans, he said.

Therefore, to pre-empt the pandemic, scientists will need to work with government agencies and international funding bodies to do risk assessment and prepare countermeasures to prevent virus spread.

The second level would be the early warning stage. When there are severe, unusual cases in the intensive care unit or local clinics, it could be signs of a new virus.

This was the case in Wuhan, where doctors detected severe pneumonia in the hospital, and all the diagnosis for other diseases was negative.

The final level - when the virus has started to spread, the last resort would be to develop vaccines and therapeutics, said Prof Wang.

The Duke-NUS team is working on just that.

Prof Wang and his team from the medical school are developing a booster jab to offer a broader spectrum of protection for future Sars-Cov-2 variants and other coronaviruses.

This comes after his team had found that people who both recovered from severe acute respiratory syndrome (Sars) in 2003 and who received the Pfizer-BioNTech vaccine for Covid-19 are able to produce antibodies to neutralise all known Covid-19 variants of concern, such as the Delta variant.

The antibodies could possibly also tackle other potential animal coronaviruses.

The booster jab, which targets the Sars-Cov-1 virus family, which causes Sars, has been tested on mice and has so far shown to be effective, said Prof Wang.

Now that the proof of concept has worked, the team plans to start human trials.

At the same time, Prof Wang intends to recruit more recovered Sars patients from other places such as Hong Kong, Guangzhou and possibly Toronto. The researchers aim to understand the level of immunity that they are able to develop from being jabbed with a range of other vaccines such as Moderna, Sinovac or AstraZeneca.