TEDMED Speaker Daniel Streicker provided some great insights about bats and pandemics in his 2018 Talk “What vaccinating vampire bats can teach us about pandemics” and TEDMED blog post. Learn about this Animal-Borne Disease Detective’s perspective on COVID-19 in our Q & A below.
TEDMED: What do we know about the origin of COVID-19? Which theories stand strong in your mind?
Daniel Streicker: We know that SARS-CoV-2 (the virus that causes COVID-19) most likely originated from a non-human animal, but exactly which animal and how it managed to make the jump to people largely remains a mystery. The virus genome is most closely related to viruses that are known to circulate in Old World bats in the family Rhinolophidae (horseshoe bats). That points to bats in this same group as the origin, but the viruses we know about aren’t a perfect genetic match to SARS-CoV-2. In fact, there are few decades worth of transmission separating the previously known viruses from the virus that is now circulating in humans. That gap could be filled by another bat virus that we don’t know about (there are likely many undiscovered coronaviruses in bats). Alternately, a historical bat virus might have jumped into and evolved in some ‘intermediate’ host prior to infecting humans. We don’t know exactly what triggered the shift to humans, but finding the animal source would provide viral clues. Researchers are now trying to use knowledge of the biology of the virus to work out candidate animals to survey.
TM: What should we be weary of to prevent another bat initiated outbreak?
DS: Like all animals, bats host diverse viruses, some of which are able to infect humans. Consequently the main thing we can do is limit the opportunities that viruses have to spread between species. In some cases, there are practical solutions like limiting the trafficking and consumption of wildlife or improving handling and animal housing standards. However, when there are indirect routes of infection between animals and people such as through the shared environment, through arthropod vectors (ticks, mosquitoes) or through domestic animals, prevention will be challenging without larger scale changes in human societies, such as changing farming practices, land use, and resource extraction practices. COVID-19 is not the first and it is not likely to be the last disease outbreak that originates from bats.
TM: Are there ways to take precautions against animal to human transmission for new diseases? Or is it inevitable?
DS: Unfortunately, some amount of animal to human transmission is inevitable. The positive side is that with each epidemic we gain new knowledge and technologies that let us respond faster. It also puts one more high-risk virus on our radar which might be prevented from re-emerging in the future. We can also do more now than ever before to prepare. The more we understand the routes through which animal viruses emerge, the more we can develop broad-acting precautionary measures to reduce the risk. For example, limiting human-wildlife interaction in high risk situations. However, we also have new tools that are allowing viruses to be discovered at unprecedented rates. More comprehensive knowledge of viral diversity can accelerate investigations into the origins of novel viruses that appear in humans. This cataloging of viruses is also a first step towards evaluating risk prior to emergence in humans, though we still need better ways to narrow the list of viruses that are worth preemptively investigating.
TM: Was there anyway for the world to anticipate this virus? What additional complications arise given that this is a novel virus?
DS: We couldn’t have predicted this exact virus, but given that the SARS outbreak of 2002-2003 was caused by a very similar virus (taxonomically the same species as the virus that causes COVID-19), it is really not a surprise. In the wake of SARS, a great deal of surveillance was undertaken to discover and characterize coronaviruses in wild animals, and numerous scientists provided persuasive evidence that these kinds of viruses were circulating in bats and posed a threat to human health. Why more effort was not put into developing vaccines and antivirals for humans is perplexing.
TM: Once we understand the source of COVID-19, and eventually develop a vaccine, should efforts be put into tracking and vaccinating the source animal – as you suggested for rabies in vampire bats?
DS: If this is a virus that is transmitted in nature by a wide variety of bat species, vaccination would be challenging. If emergence in humans turns out to be the consequence of a rare evolutionary change in an intermediate host, vaccinating that host could be practical. On the other hand, it could be that transmission in the intermediate host was short lived and it has now gone extinct from animals. In that case re-emergence would be relatively unlikely even without human intervention. The bottom line is that we need to know the steps that the virus took between bat and human to know where the most effective interventions should be targeted.