Humans transmit more viruses to domestic and wild animals than we contract from them

Teresa Guerrero Madrid

Madrid

Updated Monday, March 25, 2024-14:02

Ebola, Covid-19 and avian influenza have highlighted in recent years the serious problem, both public health and economic, of the transmission of diseases between animals and humans. This Monday, new research on this matter brings a striking conclusion: humans transmit more viruses to domestic and wild animals than we contract from them.

This is stated by a team from University College London in the journal

Nature Ecology & Evolution

after carrying out an extensive analysis of virus genomes, specifically, 12 million viral genomes that were conserved in public databases.

Most emerging and re-emerging infectious diseases are caused by viruses circulating in animals

. When they move from vertebrate animals to humans, a process known as zoonosis, they can cause outbreaks of diseases such as avian flu or Covid-19 (caused by the SARS-CoV-2 coronavirus), with the capacity to cause epidemics and pandemics. . The

close interaction between men and animals,

added to the increase in commercial activity and mobility, is favoring the greater spread of zoonoses. Furthermore, the spread of these diseases is also favored by climate change and the extension of agricultural practices to areas where wild animals live, since in addition to destroying their habitat, contact is encouraged.

Due to the enormous impact of zoonotic diseases on public health, humans have been considered a sink of viruses rather than a source, and

the transmission of viruses from people to animals has generally received much less attention.

Therefore, the result of this work has surprised its authors, as doctoral student

Cedric Tan

, leader of the study and researcher linked to the Institute of Genetics of University College London and the Francis Crick Institute, admits to this newspaper.

"Infectious disease researchers largely know that people transmit viruses to animals. A famous example is the multiple outbreaks of [coronavirus] SARS-CoV-2 in mink farms around the world, once the virus spread. spread globally among humans. However,

it has been unexpected that we transmit more viruses to animals than they transmit to us

," says Tan, who considers that these results "highlight our enormous impact on the environment and animals that surround us."

To know more

Health.

Contagion in minks complicates the worst avian flu season in Spain: "It is a ticking bomb"

• Editor: TERESA GUERRERO

• Editor: CRISTINA G. LUCIO Madrid

• Editorial: ÁNGEL NAVARRETE Photos

Contagion in minks complicates the worst avian flu season in Spain: "It is a ticking bomb"

Science.

The collateral victims of the pandemic: is it necessary to vaccinate animals?

• Editor: TERESA GUERRERO Madrid

The collateral victims of the pandemic: is it necessary to vaccinate animals?

For the study, this team developed and applied methodological tools with which they analyzed those almost 12 million viral genomes that, as detailed by Cedrin Tan, were sent by several laboratories around the world to the public database, NCBI Virus. Taking advantage of this data,

they reconstructed the evolutionary histories and past jumps of viruses in the host in 32 viral families,

and looked for which parts of the viral genomes acquired mutations during the host jumps.

Their analysis revealed that about twice as many host jumps occurred from humans to other animals (known as anthroponosis). This pattern was consistent in the majority of the viral families analyzed. Likewise, they found even more host jumps from animal to animal, which did not involve humans.

As Tan explains, the Covid-19 pandemic was one of the triggers that drove this extensive genomic research carried out at University College London: "SARS-CoV-2, the causative agent of the pandemic, is believed to have originated in horseshoe bats and jumped to humans, possibly via an animal species that has not yet been identified.

The emergence of SARS-CoV-2 in humans in late 2019 was a stark reminder of the massive impacts that jumping has of viral hosts in public health

," states the scientist. "However, we also realized that we often focus on viruses that can jump from animals to humans (i.e. zoonotic viruses), largely overlooking the fact that viruses

can jump from humans to animals and "also among animals.

Therefore, we set out to investigate the patterns and drivers of viral host jumping in all vertebrates, including domestic and wild animal species."

As Tan warns, "animals contracting viruses from humans can not only harm the animal and pose a potential conservation threat to the affected species, but

can also cause new problems for humans by affecting food security

in in the event that it is necessary to sacrifice large quantities of livestock to avoid an epidemic, as has been happening in recent years with the H5N1 strain of avian flu.

Furthermore, he adds, "if a human-carried virus infects a new animal species, the virus could continue to thrive even if it is eradicated among humans, or even

develop new adaptations

before ending up infecting humans again."

Prepare for future epidemics

In this sense, Francois Balloux, co-author of the study and researcher at the Institute of Genetics at University College London, highlights in a statement that "by studying and monitoring the transmission of viruses between animals and humans, in any direction, we can better understand the evolution and hopefully be better prepared for future outbreaks and epidemics of new diseases, while also helping conservation efforts.

Asked if they have identified certain animal species that are more vulnerable to contracting diseases that humans have, Cedrid Tan points out that this is an issue that they will address in their future research.

As for what can be done to try to limit disease transmissions from people to animals, Tan says his study "highlights the underestimated frequency of viral host jumps from humans to animals," which serves to create awareness about the impacts of human viruses on animals:

"We have identified the problem, but we are only at the first step in solving it.

We would recommend greater genomic surveillance efforts in a broader range of animal species to better understand the diversity of viruses that circulate in animals before we can begin to study their impacts on animal health," he proposes.