Because early reports of the COVID-19 epidemic came out of Wuhan, China, it’s easy to assume that the virus reached the UK directly from that country – but according to a new study, that’s not the case. The report also discredits the theory of a ‘patient zero’ bringing the infection into the country, suggesting that there may have been at least 1,300 sources, most of them from Europe.
The study, by the Covid-19 Genomics UK consortium (Cog-UK), analysed the genetic code of viral samples taken from more than 20,000 people infected with coronavirus in the UK, and built up a ‘family tree’ of infection combined with travel on international travel.
The conclusion was that the UK’s coronavirus epidemic had not one origin, but more like 1,356 occasions on which somebody brought the infection into the UK from abroad.
“The surprising and exciting conclusion is that we found the UK epidemic has resulted from a very large number of separate importations,” said Prof Nick Loman, from Cog-UK and the University of Birmingham.
The study showed that less than 0.1 percent of the imported cases came directly from Wuhan, China – instead the UK’s coronavirus epidemic was largely initiated by travel from Italy in late February, Spain in early-to-mid-March and then France in mid-to-late-March.
“The big surprise for us was how fluid the process was, the rate of and source of virus introduction shifted rapidly over the course of only a few weeks,” said Prof Oliver Pybus, from the University of Oxford. “This happened later than perhaps we would have expected, with 80 percent of those initial cases arriving in the country between 28th Feb and 29th March.”
Chains of transmission
At that time the government was still debating whether it should lock down the country, and hadn’t even considered closing borders to travellers – and after this date, the pandemic spread of its own accord, with few additional imported cases.
“If there’s good news here, these chains of transmission were and are being suppressed and going extinct as a result of social distancing and we continue to see that now,” Prof Loman said.
A recent study concludes that there’s no credible evidence of genetic engineering of the COVID-19 virus. While conspiracy theorists promote the view that the virus was engineered in a lab in China, the report by the Centre for Retrovirus Research at Ohio State University says: “Currently, there are speculations, rumours and conspiracy theories that SARS-CoV-2 is of laboratory origin. Some people have alleged that the human SARS-CoV-2 was leaked directly from a laboratory in Wuhan where a bat CoV (RaTG13) was recently reported, which shared ∼96% homology with the SARS-CoV-2.
“However, as we know, the human SARS-CoV and intermediate host palm civet SARS-like CoV shared 99.8% homology… it is highly unlikely that RaTG13 CoV is the immediate source of SARS-CoV-2.
“The absence of a logical targeted pattern in the new viral sequences and a close relative in a wildlife species (bats) are the most revealing signs that SARS-CoV-2 evolved by natural evolution. A search for an intermediate animal host between bats and humans is needed to identify animal CoVs more closely related to human SARS-CoV-2.
“There is speculation that pangolins might carry CoVs closely related to SARS-CoV-2, but the data to substantiate this is not yet published.”
Another claim in Chinese social media points to a Nature Medicine paper published in 2015 which reports the construction of a chimeric CoV (an organism carrying more than one type of DNA) with a bat CoV S gene (SHC014) in the backbone of a SARS CoV that has adapted to infect mice (MA15) and is capable of infecting human cells. The Ohio report states “This claim lacks any scientific basis and must be discounted because of significant divergence in the genetic sequence of this construct with the new SARS-CoV-2 (>5,000 nucleotides)… there is no credible evidence to support the claim that the SARS-CoV-2 is derived from the chimeric SL-SHC014-MA15 virus..”
Civets were proposed to be an intermediate host of the bat-CoVs, capable of spreading SARS CoV to humans, but in 2013 several novel bat coronaviruses were isolated from Chinese horseshoe bats, and combined with evolutionary evidence that the bat ACE2 gene has been positively selected at the same contact sites as the human ACE2 gene for interacting with SARS CoV , it was proposed that an intermediate host may not be necessary and that some bat SL-CoVs may be able to directly infect human hosts.
The Ohio study also dismisses rumours that the SARS-CoV-2 was artificially, or intentionally, made by humans in the lab, as highlighted in one manuscript submitted to BioRxiv (a manuscript sharing site prior to any peer review), claiming that SARS-CoV-2 has HIV sequence in it and was thus likely generated in the laboratory. In a rebuttal paper led by an HIV-1 virologist Dr. Feng Gao, they used careful bioinformatics analyses to demonstrate that the original claim of multiple HIV insertions into the SARS-CoV-2 is not HIV-1 specific but random. Because of the many concerns raised by the international community, the authors who made the initial claim have already withdrawn this report.
The Ohio report concludes: “Evolution is stepwise and accrues mutations gradually over time, whereas synthetic constructs would typically use a known backbone and introduce logical or targeted changes instead of the randomly occurring mutations that are present in naturally isolated viruses such as bat CoV RaTG13.
“In our view, there is currently no credible evidence to support the claim that SARS-CoV-2 originated from a laboratory-engineered CoV. It is more likely that SARS-CoV-2 is a recombinant CoV generated in nature between a bat CoV and another coronavirus in an intermediate animal host.
“More studies are needed to explore this possibility and resolve the natural origin of SARS-CoV-2. We should emphasize that, although SARS-CoV-2 shows no evidence of laboratory origin, viruses with such great public health threats must be handled properly in the laboratory and also properly regulated by the scientific community and governments.”
Whatever the origin of the COVID-19 virus, while early reports of the epidemic coming out of Wuhan, China, make it easy to assume that the virus reached the UK directly from that country, according to current thinking, that’s not the case.