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Humans transmit more viruses to animals than we catch from them

A team of researchers from the University College London (UCL) has recently found that humans transmit viruses to domestic and wild animals more frequently than they contract them from these animals. This major analysis of viral genomes offers new insights into the dynamics of disease transmission across species.

Through an exhaustive examination of all publicly available viral genome sequences, the experts aimed to trace the cross-species transmission – or host jumps – of viruses. 

Are humans at the receiving end of viruses?

The team sought to challenge the prevailing view that humans are primarily at the receiving end of zoonotic diseases, which are infections that jump from animals to humans. These diseases have been responsible for outbreaks such as Ebola, flu, and COVID-19.

The research team developed and applied methodological tools to analyze the nearly 12 million viral genomes that have been published on public databases to date, outlining the scale of their investigation into the evolutionary paths and mutations of viruses as they adapt to new hosts.

Bidirectional exchange of pathogens

Contrary to the common perception of humans as mere recipients of animal viruses, the study’s findings suggest a more bidirectional exchange of pathogens. 

“We should consider humans just as one node in a vast network of hosts endlessly exchanging pathogens, rather than a sink for zoonotic bugs,” said co-author Francois Balloux, a professor at the UCL Genetics Institute.

“By surveying and monitoring transmission of viruses between animals and humans, in either direction, we can better understand viral evolution and hopefully be more prepared for future outbreaks and epidemics of novel illnesses, while also aiding conservation efforts.”

How do me viruses emerge in humans and animals?

Study lead author Cedric Tan, a PhD student at the UCL Genetics Institute and Francis Crick Institute, pointed out the broader implications of their findings, especially concerning conservation and food security. 

“When animals catch viruses from humans, this can not only harm the animal and potentially pose a conservation threat to the species, but it may also cause new problems for humans by impacting food security if large numbers of livestock need to be culled to prevent an epidemic, as has been happening over recent years with the H5N1 bird flu strain.”

“Additionally, if a virus carried by humans infects a new animal species, the virus might continue to thrive even if eradicated among humans, or even evolve new adaptations before it winds up infecting humans again. 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.”

Viruses with a wider range of animal hosts 

Interestingly, viruses with a wider range of animal hosts showed a lesser need for such adaptations, suggesting inherent capabilities in some viruses to infect diverse hosts without extensive genetic changes.

While cell entry is generally considered as the first step for a virus to infect a host, the scientists discovered that many of the adaptations associated with host jumps were not found in the viral proteins which enable them to attach to and enter host cells. This finding suggests that viral host adaptation is a complex process in need of further research to be fully understood.

Enhancing our understanding of host jumps 

“Our research was made possible only by the countless research teams that have openly shared their data via public databases. The key challenge, moving forward, is to integrate the knowledge and tools from diverse disciplines including genomics, epidemiology, and ecology to enhance our understanding of host jumps,” said co-author Lucy van Dorp, a researcher in microbial and population genetics at UCL.

Thus, the study, published in the journal Nature Ecology & Evolution, not only sheds light on the underestimated role of humans in transmitting viruses to other species but also underscores the importance of a holistic approach to monitoring and managing disease outbreaks, reinforcing the need for a One Health perspective that recognizes the health of humans, animals, and the environment as interconnected.


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