Key points:
- Humans pass approximately twice as many viruses to animals as they catch from them.
- Viral jumps from humans to animals were associated with an increase in genetic mutations.
- Understanding how and why viruses jump will help scientists determine how new viral diseases emerge in both humans and animals.
New research finds that humans pass more viruses to domestic and wild animals than they catch from them. The findings, published in Nature Ecology & Evolution, highlight the importance of examining human-to-animal transmission of viruses and its impact on public health.
Researchers developed and applied methodological tools to analyze nearly 12 million viral genomes present on public databases. With this data, they reconstructed the evolutionary histories and past host jumps of viruses across 32 viral families. More specifically, they focused on which parts of the viral genome acquired mutations during host jumps.
The research team found that approximately twice as most host jumps occurred from humans to other animals—called anthroponosis—instead of the other way around in a process called zoonosis. This pattern was the case for most of the viral families examined.
“We should consider humans just as one node in a vast network of hosts endlessly exchanging pathogens, rather than sink for zoonotic bugs,” said study co-author Francois Balloux, professor at University College London (UCL).
Researchers also found that, on average, viral jumps were associated with an increase in genetic mutations in viruses compared to their continued evolution in just one host animal. This finding suggests that viruses must adapt to better exploit hosts. Many of the adaptations linked to host jumps were not found in viral proteins that allow them to attach and enter host cells, indicating that adaptation is a complex and mysterious process.
“Understanding how and why viruses evolve to jump into different hosts across the wider tree of life may help us figure out how new viral diseases emerge in humans and animals,” explained lead author Cedric Tan of UCL.