- Zoonotic diseases like influenza and many coronaviruses start out in animals, but their biological machinery often enables them to jump to humans.
- MERS-CoV and SARS-CoV appear to originate in animals, and the same is likely true of SARS-CoV-2. This makes them zoonoses, diseases that can jump between humans and other animals.
- While the specifics differ, the viral mechanism relies on the same fundamental premise: access and ability.
An article in Science Focus, written by Katherine Arden, explains How do viruses jump from animals to humans.
Zoonotic viruses
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.
Development of variants
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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Source: Science Focus
