Q: Why are bat-borne diseases so common? Is this an effect of human encroachment on bat habitats or a change in bat behaviour?
Prof Wang Linfa: Bats have been around for 60 million to 80 million years. They are more ancient than humans and they have been peacefully co-existing with viruses.
Bats carry many more viruses than any other mammal, but bat viruses usually do not jump species until a susceptible intermediate host, such as a civet, pangolin or pig, comes along.
Definitely, in the last few decades, intensive farming, wildlife farming and also climate change have all contributed to bats now making contact with more animals, raising the chances of them transmitting viruses to intermediate hosts.
Once the virus gets amplified, like with Nipah in pigs, it gets transmitted to humans.
Q: Do you believe serology can indicate effective immunity to Covid-19? When can we use serology to know if it is safe for healthcare workers to work in the front line?
Prof Wang: To use serology to indicate correlation with protection (against the virus), you have to know two things.
First, you are measuring the population of neutralising antibodies.
When you get infected, your body launches antibodies and there are two types.
One just looks for the virus, but the virus can still get into your cells.
The other is neutralising antibodies which prevent the virus from getting into cells. Such antibodies most likely correlate with protection.
ABOUT THE SERIES
Covid-19: Updates from Singapore is a 12-episode weekly webinar series organised by the National University of Singapore (NUS), National University Health System and the World Health Organisation's Global Outbreak Alert and Response Network (GOARN).
• Professor Dale Fisher, professor of medicine, NUS Yong Loo Lin School of Medicine, and chair of GOARN
• Dr David Allen, visiting senior fellow, Courage Fund Visiting Professorship, NUS Yong Loo Lin School of Medicine
EPISODE 1 GUEST: Professor Paul Tambyah, professor of medicine, NUS Yong Loo Lin School of Medicine
EPISODE 2 GUEST: Professor Wang Linfa, director of emerging infectious diseases programme, Duke-NUS Medical School
I have developed an assay (test) and we are going to measure neutralising antibodies, so the first part of the equation is solved.
But the second part of it is much more difficult: Does the level of neutralising antibodies correlate with protection in vivo (in a live subject, as opposed to in vitro, or in a cell culture)?
This is a much more difficult question to answer. We need more recovered and recovering patients, and we need to monitor them for much longer than the two months we have had.
We're working very hard but, to answer the second part of that question, we need more time and more samples.
Q: There have been theories that Sars-CoV-2 was synthesised in a laboratory and not naturally occurring. Is there evidence to support or debunk this?
Prof Wang: This is a very politically sensitive topic but there are many papers on it.
All the leading scientists say there is zero chance that happened.
Q: There are many comments on replicating the Singapore approach in countries like the United States. How realistic is this? For example, can contact tracing as it is done in Singapore be scaled to a country like the US?
Prof Dale Fisher: Yes and no.
The concept of all those interventions - such as early detection, isolation, contact tracing and quarantining - has to stay true.
But how are you going to do it in a different setting and how will it get adapted?
What is the community's tolerance for privacy intrusions or loss of freedom by quarantining and isolation?
These are things the world is getting a bit more comfortable with now that they can see the consequences of not containing the virus.
I won't say what's happening in Singapore can be replicated in other countries necessarily, but the principles can be.
Q: What are the best strategies for combating Covid-19 in developing countries with limited resources?
Prof Paul Tambyah: The key is still clinical diagnosis.
Even though a lot of low-and middle-income countries have limited resources, this is an opportunity for the world to step in. Nobody is safe until everybody is safe.
We've seen this with The Global Fund to Fight Aids, Tuberculosis (TB) and Malaria.
A TB polymerase chain reaction (PCR) test has been rolled out across the world. We've got desktop PCR kits which are being used.
This outbreak has highlighted the need for usable point-of-care diagnostics like the PCR kits.