London – It's natural for humans to worry about contracting pathogens from all kinds of wild animals. But new research suggests that humans tend to be more contagious than the creatures we fear. Following new analysis of the virus's genome, scientists at University College London report that humans transmit more viruses to livestock and wildlife than vice versa.
The researchers analyzed all publicly available viral genome sequences to reconstruct instances in which a virus jumped from one host and infected another vertebrate species.
In general, many emerging and re-emerging infectious diseases are caused by animal viruses. When these pathogens are transmitted from animals to humans (a process called zoonotic disease), they can cause outbreaks and epidemics of diseases such as Ebola and new strains of influenza. Given the enormous impact that zoonotic diseases have on public health, humans have historically been viewed as a “sink” rather than a source of viruses. In other words, human-to-animal virus transmission usually receives less attention.
In this latest study, the study authors developed and applied methodological tools to analyze nearly 12 million viral genomes stored in public databases to date. By leveraging this data, the researchers were able to reconstruct the evolutionary history and past host jumps of viruses across 32 virus families. This allowed them to search for which specific regions of the viral genome underwent mutations during the host jump.
Researchers estimate that there are about twice as many host jumps from humans to other animals (known as). human syndrome) rather than the other way around. This pattern was consistent across most of the considered virus families. Additionally, this study reports many more animal-to-animal host transfers that do not involve humans at all.
This study highlights the much-admired fact that human viruses frequently spread from humans to both wild and domestic animals.
“We need to think of humans not as sources of zoonotic diseases, but simply as nodes in a vast network of hosts that endlessly exchange pathogens,” said study co-author Professor François Barrault. (UCL Institute of Genetics) said in a media release. “In both directions, investigating and monitoring the transmission of viruses between animals and humans can help us better understand their evolution, improve our preparedness for future new disease outbreaks and epidemics, and protect us.” We hope to be able to support these activities as well.”
On average, virus host jumping is associated with increased genetic changes or mutations in the virus compared to continuous evolution with just one host animal. The study authors say this reflects how viruses must adapt to successfully take advantage of new hosts.
It is also noteworthy that viruses that are already known to infect many different animals have weaker signals for this adaptive process. This indicates that viruses with wider host ranges may inherently possess properties that increase their ability to infect more hosts. Other viruses may require more extensive adaptations to infect new host species.
“If animals receive the virus from humans, it can not only harm the animals and pose a potential threat to the conservation of the species, but it may also be necessary to kill large numbers of livestock to prevent virus transmission. , which could affect food security and pose new problems for humans.'' Epidemics are occurring, as has happened with the H5N1 avian influenza strain in recent years,'' said study lead author and Ph.D. student Cedric Tan (UCL Institute of Genetics and Francis Crick Institute) explains.
“Furthermore, if a human-borne virus infects a new animal species, the virus may continue to proliferate even if it is eradicated among humans, or it may evolve new adaptations before infecting humans again. It's even possible. Understanding how and why viruses evolve to jump into different hosts across the broader tree of life could help us understand how new viral diseases arise in humans and animals. It could be helpful.”
Cell entry is usually considered the first step for a virus to infect a host. However, the researchers note that many of the adaptations implicated in host jumping are not found in the viral proteins that allow the virus to attach to and enter host cells. This indicates that viral host adaptation is a complex process that is not yet fully understood.
“Our work has only been made possible by countless research teams openly sharing their data through public databases.” “We aim to integrate knowledge and tools from across the world to improve our understanding of host jumping,” concluded study co-author Dr Lucie van Dorp (UCL Institute of Genetics).
The research will be published in a journal Natural ecology and evolution.
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