Izvor Covid-19 – Posledica naravnega razvoja ali umetnega izvora? (2)

Nekatera dejstva, ki jih morajo preiskave seveda nedvoumno dokazati, kažejo, da bi Covid-19 lahko bil posledica izbruha virusa iz laboratorija v Wuhanu. V Wuhanu sta sicer dva laboratorija, v obeh pa se ukvarjajo s poskusi, ali je možen preskok živalskega koronavirusa v človeškega. V bolj znanem od obeh, Wuhan Institute of Virology (WIV), so preiskovali vzorce krvi iz pljuč rudarjev v Mojiangu, ki so zboleli ali umrli za koronavirusom netopirjev iz leta 2012. Hipotezo sta razvila Virolog Jonathan Latham in genetičarka Allison Wilson. Kratek povzetek hipoteze je naslednji:

Rudarji v Mojiangu naj bi se prvotno okužili z RaTG13 in / ali podobnimi koronavirusi med njihovim dvotedenskiom bivanjem v rudniškem jašku, kjer so vdihovali aerosole iz blata netopirjev. RaTG13 naj bi se nato z mutacijami in / ali rekombinacijami v pljučih rudarjev med njihovo štirimesečno hospitalizacijo v bolnišnici spremenil v SARS-CoV-2 (ali predhodni virus). Tako so okužena pljuča rudarjev morda služila kot „človeški inkubator“, ki je RaTG13 omogočil, da se je prilagodil tako človeškemu celičnemu receptorju ACE2 kot človeškemu imunskemu sistemu v samo štirih mesecih, namesto v nekaj desetletjih, kot bi pričakovali pri naravni evoluciji virusa. Inštitut v Wuhanu je v letih 2012/2013 prejel vzorce tkiva in krvi preživelih ali mrtvih rudarjev, ki so morda že vključevali SARS-CoV-2 (ali njegov predhodnik). Virologi WIV so nato morda čakali še pet let, dokler niso zaključili svojega laboratorija BSL-4 v letu 2017/2018, preden so začeli raziskovati tako imenovani SARS-CoV-2. SARS-CoV-2 je morda jeseni 2019 pobegnil iz laboratorija WIV, morda prek okuženega laboratorijskega delavca ali trupla živali, in sprožil današnjo globalno pandemijo koronavirusa.

V nadaljevanju je nekaj odlomkov iz njunega članka, v katerem sta razvila hipotezo in med drugim zavrgla trditev široko citirane analize Andersena et al (2020), da je Covid-19 posledica naravnega razvoja in da epidemija Covid-19 ne more biti posledica izbruha virusa iz laboratorija.

In all the discussions of the origin of the COVID-19 pandemic, enormous scientific attention has been paid to the molecular character of the SARS-CoV-2 virus, including its novel genome sequence in comparison with its near relatives. In stark contrast, virtually no attention has been paid to the physical provenance of those nearest genetic relatives, its presumptive ancestors, which are two viral sequences named BtCoV/4991 and RaTG13.

This neglect is surprising because their provenance is more than interesting. BtCoV/4991 and RaTG13 were collected from a mineshaft in Yunnan province, China, in 2012/2013 by researchers from the lab of Zheng-li Shi at the Wuhan Institute of Virology (WIV). Very shortly before, in the spring of 2012, six miners working in the mine had contracted a mysterious illness and three of them had died (Wu et al., 2014). The specifics of this mystery disease have been virtually forgotten; however, they are described in a Chinese Master’s thesis written in 2013 by a doctor who supervised their treatment.

We arranged to have this Master’s thesis translated into English. The evidence it contains has led us to reconsider everything we thought we knew about the origins of the COVID-19 pandemic. It has also led us to theorise a plausible route by which an apparently isolated disease outbreak in a mine in 2012 led to a global pandemic in 2019.

The origin of SARS-CoV-2 that we propose below is based on the case histories of these miners and their hospital treatment. This simple theory accounts for all the key features of the novel SARS-CoV-2 virus, including ones that have puzzled virologists since the outbreak began.

The theory can account for the origin of the polybasic furin cleavage site, which is a region of the viral spike protein that makes it susceptible to cleavage by the host enzyme furin and which greatly enhances viral spread in the body. This furin site is novel to SARS-CoV-2 compared to its near relatives (Coutard, et al., 2020). The theory also explains the exceptional affinity of the virus spike protein for human receptors, which has also surprised virologists (Letko et al., 2020; Piplani et al, 2020; Wrapp et al., 2020; Walls et al., 2020). The theory further explains why the virus has barely evolved since the pandemic began, which is also a deeply puzzling aspect of a virus supposedly new to humans (Zhan et al., 2020; van Dorp et al., 2020; Chaw et al., 2020). Lastly, the theory neatly explains why SARS-CoV-2 targets the lungs, which is unusual for a coronavirus (Huang et al., 2020).

We do not propose a specifically genetically engineered or biowarfare origin for the virus but the theory does propose an essential causative role in the pandemic for scientific research carried out by the laboratory of Zheng-li Shi at the WIV; thus also explaining Wuhan as the location of the epicentre.

Why has the provenance of RaTG13 and BtCoV/4991 been ignored?

The apparent origin of the COVID-19 pandemic is the city of Wuhan in Hubei province, China. Wuhan is also home to the world’s leading research centre for bat coronaviruses. There are two virology labs in the city, both have either collected bat coronaviruses or researched them in the recent past. The Shi lab, which collected BtCoV/4991 and RaTG13, recently received grants to evaluate by experiment the potential for pandemic pathogenicity of the novel bat coronaviruses they collected from the wild.

To add to these suggestive data points, there is a long history of accidents, disease outbreaks, and even pandemics resulting from lab accidents with viruses (Furmanski, 2014; Weiss et al., 2015). For these and other reasons, summarised in our article The Case is Building that COVID-19 Had a Lab Origin, we (a virologist and a geneticist) and others have concluded that a lab outbreak is a credible thesis. Certainly, a lab origin has at least as much circumstantial evidence to support it as does any natural zoonotic origin theory (Piplani et al., 2020; Segreto and Deigin, 2020; Zhan et al., 2020).

The media, normally so enamoured of controversy, has largely declined even to debate the possibility of a laboratory escape. Many news sites have simply labelled it a conspiracy theory.

The principal reason for media dismissals of the lab origin possibility is a review paper in Nature Medicine (Andersen et al., 2020). Although by Jun 29 2020 this review had almost 700 citations it also has major scientific shortcomings. These flaws are worth understanding in their own right but they are also useful background for understanding the implications of the Master’s thesis.

Andersen et al., a critique

The question of the origin of the COVID-19 pandemic is, in outline, simple. There are two incontrovertible facts. One, the disease is caused by a human viral pathogen, SARS-CoV-2, first identified in Wuhan in December 2019 and whose RNA genome sequence is known. Second, all of its nearest known relatives come from bats. Beyond any reasonable doubt SARS-CoV-2 evolved from an ancestral bat virus. The task the Nature Medicine authors set for themselves was to establish the relative merits of each of the various possible routes (lab vs natural) by which a bat coronavirus might have jumped to humans and in the same process have acquired an unusual furin site and a spike protein having very high affinity for the human ACE2 receptor.

When Andersen et al. outline a natural zoonotic pathway they speculate extensively about how the leap might have occurred. In particular they elaborate on a proposed residence in intermediate animals, likely pangolins. For example, “The presence in pangolins of an RBD [Receptor Binding Domain] very similar to that of SARS-CoV-2 means that we can infer that this was probably in the virus that jumped to humans. This leaves the insertion of [a] polybasic cleavage site to occur during human-to-human transmission.” This viral evolution occurred in “Malayan pangolins illegally imported into Guangdong province”. Even with these speculations there are major gaps in this theory. For example, why is the virus so well adapted to humans? Why Wuhan, which is 1,000 Km from Guangdong?

We propose that, when frozen samples derived from the miners were eventually opened in the Wuhan lab they were already highly adapted to humans to an extent possibly not anticipated by the researchers. One small mistake or mechanical breakdown could have led directly to the first human infection in late 2019.

Thus, one of the miners, most likely patient 3, or patient 4 (whose thymus was removed), was effectively patient zero of the COVID-19 epidemic. In this scenario, COVID-19 is not an engineered virus; but, equally, if it had not been taken to Wuhan and no further molecular research had been performed or planned for it then the virus would have died out from natural causes, rather than escaped to initiate the COVID-19 pandemic.

Evidence in favour of the MMP proposal

Our proposal is consistent with all the principal undisputed facts concerning SARS-CoV-2 and its origin. The MMP proposal has the additional benefit of reconciling many observations concerning SARS-CoV-2 that have proven difficult to reconcile with any natural zoonotic hypothesis.

For instance, using different approaches, numerous researchers have concluded that the SARS-CoV-2 spike protein has a very high affinity for the human ACE2 receptor (Walls et al., 2020; Piplani et al., 2020; Shang and Ye et al., 2020; Wrapp et al., 2020). Such exceptional affinities, ten to twenty times as great as that of the original SARS virus, do not arise at random, making it very hard to explain in any other way than for the virus to have been strongly selected in the presence of a human ACE2 receptor (Piplani et al., 2020).

In addition to this, a recent report found that the spike of RaTG13 binds the human ACE2 receptor (Shang and Ye et al., 2020). We proposed above that the virus in the mine directly infected humans lung cells. The main determinant of cell infection and species specificity of coronaviruses is initial receptor binding (Perlman and Netland, 2009). Thus RaTG13, unlike most bat coronaviruses, probably can enter and infect human cells, providing biological plausibility to the idea that the miners became infected with a coronavirus resembling RaTG13.

Moreover, the receptor binding domain (RBD) of SARS-CoV-2, which is the region of the spike that physically contacts the human ACE2 receptor, has recently been crystallised to reveal its spatial structure (Shang and Ye et al., 2020). These authors found close structural similarities between the spikes of SARS-CoV-2 and RaTG13 in how they bound the human ACE2 receptor:

“Second, as with SARS-CoV-2, bat RaTG13 RBM [a region of the RBD] contains a similar four-residue motif in the ACE2 binding ridge, supporting the notion that SARS-CoV-2 may have evolved from RaTG13 or a RaTG13-related bat coronavirus (Extended Data Table 3 and Extended Data Fig. 7). Third, the L486F, Y493Q and D501N residue changes from RaTG13 to SARS CoV-2 enhance ACE2 recognition and may have facilitated the bat-to-human transmission of SARS-CoV-2 (Extended Data Table 3 and Extended Data Fig. 7). A lysine-to-asparagine mutation at the 479 position in the SARS-CoV RBD (corresponding to the 493 position in the SARS-CoV-2 RBD) enabled SARS-CoV to infect humans. Fourth, Leu455 contributes favourably to ACE2 recognition, and it is conserved between RaTG13 and SARS CoV-2; its presence in the SARS CoV-2 RBM may be important for the bat-to-human transmission of SARS-CoV-2″ (Shang and Ye et al., 2020). (italics added)

The significance of this molecular similarity is very great. Coronaviruses have evolved a diverse set of molecular solutions to solve the problem of binding ACE2 (Perlman and Netland, 2009; Forni et al., 2017). The fact that RaTG13 and SARS CoV-2 share the same solution makes RaTG13 a highly likely direct ancestor of Sars-CoV-2.

A further widely noted feature of SARS-CoV-2 is its furin site (Coutard et al., 2020). This site is absent from RaTG13 and other closely related coronaviruses. The most closely related virus with such a site is the highly lethal MERS (which broke out in 2012). Possession of a furin site enables SARS-CoV-2 (like MERS) to infect lungs and many other body tissues (such as the gastrointestinal tract and neurons), explaining much of its lethality (Hoffman et al., 2020; Lamers et al., 2020). However, no convincing explanation for how SARS-CoV-2 acquired this site has yet been offered. Our suggestion is that it arose due to the high selection pressure which existed in the miner’s lungs and which in general worked to ensure that the virus became highly adapted to the lungs. This explanation, which encompasses how SARS-CoV-2 came to target lung tissues in general, is an important aspect of our proposal.

The implication is therefore that the furin site was not acquired by recombination with another coronavirus and simply represents convergent evolution (as suggested by Andersen et al., 2020).

An intriguing alternative possibility is that SARS-CoV-2 acquired its furin site directly from the miner’s lungs. Humans possess an epithelial sodium channel protein called ENaC-a whose furin cleavage site is identical over eight amino acids to SARS-CoV-2 (Anand et al., 2020). ENaC-a protein is present in the same airway epithelial and lung tissues infected by SARS-CoV-2. It is known from plants that positive-stranded RNA viruses recombine readily with host mRNAs (Greene and Allison, 1994; Greene and Allison, 1996; Lommel and Xiong, 1991; Borja et al., 2007). The same evidence base is not available for positive-stranded animal RNA viruses, (though see Gorbalenya, 1992) but if plant viruses are a guide then acquisition of its furin site via recombination with the mRNA which encodes ENaC-a by SARS-CoV-2 is a strong possibility.

A further feature of SARS-CoV-2 has been the very limited adaptive evolution of its genome since the pandemic began (Zhan et al., 2020; van Dorp et al., 2020; Starr et al., 2020). It is a well-established principle that viruses that jump species undergo accelerated evolutionary change in their new host (e.g. Baric et al., 1997). Thus, SARS and MERS (both coronaviruses) underwent rapid and readily detectable adaptation to their new human hosts (Forni et al., 2017; Dudas and Rambaut, 2016). Such an adaptation period has not been observed for SARS-CoV-2 even though it has now infected many more individuals than SARS or MERS did. This has even led to suggestions that the SARS-CoV-2 virus had a period of cryptic circulation in humans infections that predated the pandemic (Chaw et al., 2020). The sole mutation consistently observed to accumulate across multiple studies is a D614G substitution in the spike protein (e.g. Korber et al., 2020). The numerically largest analysis of SARS-CoV-2 genomes, however, found no evidence at all for adaptive evolution, even for D614G (van Dorp et al., 2020).

The general observation is therefore that Sars-CoV-2 has remained functionally unchanged or virtually so (except for inconsequential genetic changes) since the pandemic began. This is a very important observation. It implies that SARS-CoV-2 is highly adapted across its whole set of component proteins and not just at the spike (Zhan et al., 2020). That is to say, its evolutionary leap to humans was completed before the 2019 pandemic began.

It is hard to imagine an explanation for this high adaptiveness other than some kind of passaging in a human body (Zhan et al., 2020). Not even passaging in human cells could have achieved such an outcome.

Two examples illustrate this point. In a follow up to Shang and Ye et al., (2020), a similar group of Minnesota researchers identified a distinct strategy by which the spike (S) protein (which contains the receptor bind domain; RBD) of SARS-CoV-2 evades the human immune system (Shang and Wan et al., 2020). This strategy involves more effective hiding of its RBD, but it implies again that the spike and the RBD evolved in tandem and in the presence of the human immune system (i.e. in a human body and not in tissue culture).

The Andersen authors, in their critique of a possible engineered origin for SARS-CoV-2, also stress the need for passaging in whole humans:

“Finally, the generation of the predicted O-linked glycans is also unlikely to have occurred during cell-culture passage, as such features suggest the involvement of an immune system” (Andersen et al., 2020).

The final point that we would like to make is that the principal zoonotic origin thesis is the one proposed by Andersen et al. Apart from being poorly supported this thesis is very complex. It requires two species jumps, at least two recombination events between quite distantly related coronaviruses and the physical transfer of a pangolin (having a coronavirus infection) from outside China (Andersen et al., 2020). Even then it provides no logical explanation of the adaptedness of SARS-CoV-2 across its whole genome or why the virus emerged in Wuhan.

By contrast, our MMP proposal requires only the one species jump, which is documented in the Master’s thesis. Although we do not rule out a possible role for mixed infections in the lungs of the miners, nor the possibility of recombination between closely related variants in those lungs, nor the potential acquisition of the furin site from a host mRNA, only mutation was needed to derive SARS-CoV-2 from RaTG13. Hence our attention earlier to the figure from P. Zhou et al., 2020 showing that RaTG13 is the most closely related virus to SARS-CoV-2 over its entire length. This extended similarity is perfectly consistent with a mutational origin of SARS-CoV-2 from RaTG13.

In short, the MMP theory is a plausible and parsimonious explanation of all the key features of the COVID-19 pandemic and its origin. It accounts for the propensity of SARS-CoV-2 infections to target the lungs; the apparent preadapted nature of the virus; and its transmission from bats in Yunnan to humans in Wuhan.

Further questions

The hypothesis that SARS-CoV-2 evolved in the Mojiang miner’s lungs potentially resolves many scientific questions about the origin of the pandemic. But it raises others having to do with why this information has not come to light hitherto. The most obvious of these concern the actions of the Shi lab at the WIV.

Why did the Shi lab not acknowledge the miners’ deaths in any paper describing samples taken from the mine (Ge et al., 2016 and P. Zhou et al., 2020)? Why in the title of the Ge at al. 2016 paper did the Shi lab call it an “abandoned” mine? When they published the sequence of RaTG13 in Feb. 2020, why did the Shi lab provide a new name (RaTG13) for BtCoV/4991 when they had by then cited BtCoV/4991 twice in publications and once in a genome sequence database and when their sequences were from the same sample and 100% identical (P. Zhou et al., 2020)? If it was just a name change, why no acknowledgement of this in their 2020 paper describing RaTG13 (Bengston, 2020)? These strange and unscientific actions have obscured the origins of the closest viral relatives of SARS-CoV-2, viruses that are suspected to have caused a COVID-like illness in 2012 and which may be key to understanding not just the origin of the COVID-19 pandemic but the future behaviour of SARS-CoV-2.

These are not the only questionable actions associated with the provenance of samples from the mine. There were five scientific publications that very early in the pandemic reported whole genome sequences for SARS-CoV-2 (Chan et al., 2020; Chen et al., 2020; Wu et al., 2020; P. Zhou et al., 2020; Zhu et al., 2020). Despite three of them having experienced viral evolutionary biologists as authors (George Gao, Zheng-li Shi and Edward Holmes) only one of these (Chen et al., 2020) succeeded in identifying the most closely related viral sequence by far: BtCoV/4991 a viral sequence in the possession of the Shi lab at the WIV that differed from SARS-CoV-2 by just 5 nucleotides.

As we noted in our earlier article, the most important of the questions surrounding the origins of SARS-CoV-2 could potentially be resolved by a simple examination of the complete lab notebooks and biosafety records of relevant researchers at the WIV. Now that a credible and testable lab escape hypothesis exists this task becomes potentially much easier. This moment thus represents an opportune one to renew that call for an independent and transparent investigation of the WIV.

In requesting an investigation we are aware that no scientific institution anywhere has made a comparable request. We believe that this failure undermines public trust in a “scientific response” to the pandemic. Instead, the scientific establishment has labeled the lab escape theory a “rumor“, an “unverified theory” and a “conspiracy” when its proper name is a hypothesis. By taking this stance the scientific establishment has given the unambiguous message that scientists who take the possibility of a lab origin seriously are jeopardising their careers. Thus, while countless scientific publications on the pandemic assert in their introductions that a zoonotic origin for SARS-CoV-2 is a matter of fact or near-certainty (and Andersen et al has 860 citations as of July 14th), there is still not one published scientific paper asserting that a lab escape is even a credible hypothesis that deserves investigation.

Anyone who doubts this pressure should read the interview with Birger Sørensen in Norway’s Minerva magazine in which Sørensen discusses the “reluctance” of journals to publish his assessment that the existence of a virus that is “exceptionally well adjusted to infect humans” is “suspicious” and “cannot have evolved naturally”. The source of this reluctance, says Sørensen, is not rationality or scientific evidence. It results from conflicts of interest. This mirrors our experience. To find genuinely critical analysis of COVID-19 origin theories one has to go to Twitter, blog posts, and preprint servers. The malaise runs deep when even scientists start to complain that they don’t trust science.

We nevertheless hope that journalists will investigate some of the conflicts of interest that are keeping scientists and institutions from properly investigating the lab escape hypothesis.

Vir: Jonathan Latham & Allison Wilson, Independent Science News

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