Recent studies have shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – the virus that causes COVID-19 – could have originated in bats, but it is believed that the virus may have spilled over to humans from another, as yet unknown, intermediate host.
As they are known to be natural hosts of coronaviruses, pangolins were quickly labelled as one of the prime suspects. However, a genetic analysis of a coronavirus found in pangolins carried out at the Guangdong Institute of Applied Biological Resources in China has determined that this is unlikely to be the case.
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Pangolins, sometimes known as scaly anteaters, are small to medium sized mammals that are covered in protective scales made of keratin – the same substance found in hair and fingernails. They are found across Africa and Asia and are one of the world’s most trafficked animals thanks to the widespread use of their scales in traditional medicines.
The researchers analysed the whole genome of a coronavirus identified in two groups of sick Malayan pangolins. Their findings suggest that while there are some genetic similarities between the two viruses, it is unlike that SARS-CoV-2 emerged from the pangolin coronavirus.
“Pangolins could be natural hosts of Betacoronaviruses with an unknown potential to infect humans,” the researchers said. “However, our study does not support that SARS-CoV-2 evolved directly from the pangolin-CoV.”
However, the large-scale surveillance of coronaviruses in pangolins could improve our understanding of the spectrum of coronaviruses circulating in the wild, and could help prevent and control emerging infectious diseases, the researchers say.
How do viruses jump from animals to humans?
Every animal species hosts unique viruses that have specifically adapted to infect it. Over time, some of these have jumped to humans – these are known as ‘zoonotic’ viruses.
As our populations grow, we move into wilder areas, which brings us into more frequent contact with animals we don’t normally have contact with. Viruses can jump from animals to humans in the same way that they can pass between humans, through close contact with body fluids like mucus, blood, faeces or urine.
Because every virus has evolved to target a particular species, it’s rare for a virus to be able to jump to another species. When this does happen, it’s by chance, and it usually requires a large amount of contact with the virus.
Initially, the virus is usually not well-suited to the new host and doesn’t spread easily. Over time, however, it can evolve in the new host to produce variants that are better adapted.
When viruses jump to a new host, a process called zoonosis, they often cause more severe disease. This is because viruses and their initial hosts have evolved together, and so the species has had time to build up resistance. A new host species, on the other hand, might not have evolved the ability to tackle the virus. For example, when we come into contact with bats and their viruses, we may develop rabies or Ebola virus disease, while the bats themselves are less affected.
It’s likely that bats were the original source of three recently emerged coronaviruses: SARS-CoV (2003), MERS-CoV (2012) and SARS-CoV-2, the cause of the 2019-20 coronavirus outbreak. All of these jumped from bats to humans via an intermediate animal; in the case of SARS-CoV-2, this may have been pangolins, but more research is needed.
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