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Reader Q&A: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 dont 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, its rare for a virus to be able to jump to another species. When this does happen, its 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 doesnt 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 orEbola virus disease, while the bats themselves are less affected.

Its 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 the2019-20 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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Artificial intelligence could help to predict the next virus to jump from animals to humans - BBC Science Focus Magazine