One of the things that has been obvious about COVID-19 from the start has been that it is very well adapted to humans. It has evolved a good entry system to the human airways, is often has mild symptoms, has a long pre-symptomatic infectious period, and doesn’t kill many of its hosts.
These are very good characteristics for a virus evolved to get hosts to make more copies of it’s genetic code. It gets to spread before people are aware that they have it. It didn’t cause too much alarm during its initial spread because most of its hosts got something that was like a mild flu.
By contrast, its close cousin the SARS virus wasn’t well adapted to humans. At the time it becomes infectious in a human host, the human host is aware of it. They’re running a temperature, have chills, muscle aches, headache sneezing, coughing and feeling quite sick. Those are the very things that induce people to go to doctors and hospitals. Which in turn cause our social systems to report and start to contain the disease.
Consequently SARS got identified early before it spread widely through urban populations. With its early fever aspect it was easy to test for. Elevated temperatures provided a efficient way for human societies to isolate hosts and to prevent the replication and spread of the SARS genetic code. Consequently it is effectively extinct in urban human populations
But that same subtlety of its operation has always implied that COVID-19 has been circulating in a human population for some time to evolve those characteristics. The question has where that population is?
There is a nice (but pay walled) article in the Economist that looks at this.
One of the great questions of the past six months is where sars–cov-2, the virus that causes covid-19, came from. It is thought the answer involves bats, because they harbour a variety of sars-like viruses. Yunnan, one of China’s southernmost provinces, has drawn the attention of virus hunters, as the closest-known relatives of sars–cov-2 are found there. But some think the origins of the virus are not to be found in China at all, but rather just across the border in Myanmar, Laos or Vietnam.
This is the hunch of Peter Daszak, head of EcoHealth Alliance, an organisation which researches animals that harbour diseases that move into people. Since the outbreak, in 2003, of the original sars (now known as sars–cov), scientists have paid close attention to coronaviruses. Dr Daszak says that around 16,000 bats have been sampled and around 100 new sars-like viruses discovered. In particular, some bats found in China are now known to harbour coronaviruses that seem pre-adapted to infect people. The chiropteran hosts of these viruses have versions of a protein called ace2 that closely resemble the equivalent in people. This molecule is used by sars-like viruses as a point of entry into a cell.
That such virological diversity has so far been found only in China is because few people have looked at bats in countries on the other side of the border. Yet these places are likely to be an evolutionary hotspot for coronaviruses—one that mirrors bat diversity (see map). The horseshoe bats in Yunnan which harbour close relatives of sars–cov-2 are found across the region. Other countries are thus likely to have bats with similar viral building blocks. Dr Daszak believes it is “quite likely that bats in Myanmar, Laos and Vietnam carry similar sars-related coronaviruses, maybe a huge diversity of them, and that some of them could be close to sars–cov-2”.Economist: “SARS-CoV-2 will look beyond China“
One of the strong supporting arguments to support this has been the very low rates of infection in Vietnam (412 confirmed cases) and Cambodia (198 confirmed cases). Relative to the population levels of 95+ million and 16+ million respectively, these have been extraordinarily low.
Both states are authoritarian and, especially in the case of Vietnam, have been intensely proactive with dealing with COVID-19. While there don’t appear to have been any excessive mortality level studies on these states, there also haven’t been evidence of hiding of cases either.
Vietnam is an authoritarian, one-party state which is notoriously secretive about sharing information.
But most experts believe Vietnamese authorities are being honest about coronavirus statistics.
Huong Le Thu, an analyst at the Australian Strategic Policy Institute, told the ABC that given international organisations, foreign epidemiologists and even Australia’s ambassador to Hanoi have expressed confidence in the data, she had “no reason” to doubt the figures.
The Reuters news agency reported none of the 13 funeral homes it contacted in Hanoi have seen an increase in funerals amid the pandemic.
“I know I sound like I’ve drunk the Kool-Aid, but I don’t see any alarm bells ringing about the accuracy or lack of transparency in the numbers,” said Sharon Kane, Vietnam country director at Plan International, an NGO that works on public health.Radio New Zealand: “How has Vietnam, a developing nation, had no Covid deaths?“
When you look at the list of COVID-19 cases in Vietnam or Cambodia, what does become obvious that they have excessive representation in people who grew up in other areas of the world.
John Bell, a professor of medicine at the University of Oxford, says everyone thought there would be a flood of cases in Vietnam because the country is right across the border from China. Yet Vietnam has reported only 300 in a population of 100m, and no deaths. The country did not have a great lockdown either, he adds. Nobody could work out what was going on.
One explanation, he suggests, is that Vietnam’s population is not as immunologically “naive” as has been assumed. The circulation of other sars-like viruses could have conferred a generalised immunity to such pathogens. So, if a new one emerged in the region, it was able to take hold in the human population only when it travelled all the way to central China—where people did not have this natural resistance.
This would tie in with the idea that infection with one coronavirus can provide protection against others, and that even in countries away from the evolutionary cauldron of South-East Asia part of the population may have some protection against the current pandemic. In particular, there are suggestions that protection might be conferred mainly via part of the immune system called t-cells (which work by killing virus-infected cells) rather than via antibodies (which work by gumming up pathogens). If that is the case, then serological studies which look at antibodies may be underestimating natural immunity.
All of which means that searching the reservoirs of bats of Vietnam, Cambodia, and Laos for a exact or very closer match for COVID-19 would be a good idea. Since the identification of the human corona virus in the common cold viruses back in the 1960s, we have had a number of identified epidemic outbreaks. SARS. MERS, and now COVID-19.
Each has caused a flurry of activity in various regions of the world and now at a global level. Two of these (SARS and MERS) were pretty obviously recent and ill-adapted hops from a host (probably a bat) directly or indirectly to humans. But COVID-19 appears to be exceptionally well adapted to humans and spreading in human societies. It is causing immense amounts of damage when it managed to spread out of whatever enclave where it was already endemic.
It’d appear to me that proactively knowing what is out there in the wild is the best way to prevent the next corona virus from the same enclave. It’d be rare for single virus variant to be endemic. Where there is one, there are likely to be more sharing similar characteristics.
Finding out the intermediate vector species or practices that allow the spread to a human population would also be very useful in preventing future epidemics. Because we’re going to see them as our population and practices keep expanding into wild areas, and as we keep shutting human hosts around the world to assist in their spread.
As for the mystery of the origin of covid-19, more answers will come when the who mission takes place, perhaps in August. The critical steps that led a South-East Asian bat virus to start a pandemic could have happened inside or outside of China—whether in wild-animal markets or farms, or in traders or hunters. The virus may have jumped directly from bats into people, or come via an intermediate species. The story is waiting to be told.Economist: “SARS-CoV-2 will look beyond China“
As a side note, the wacky conspiracy theories that any human was capable of designing these characteristics into a virus are pretty ludicrous. As a technical species, we simply don’t have the genetic subtlety to design something like COVID-19. Much the same applies to the idea that a release of the naturally occurring sample of the virus from a lab being of significance is just stupid and ignorant. At some stage the virus would would have escaped from whatever human enclave it was in – and infected the rest of the world.