Humans have spread their viruses to wild animals more than previously thought

Humans may be exchanging diseases with animals more frequently than previously thought. A new study shows that how pathogens spread in both directions and on a large scale needs to be monitored to more accurately assess risk, as is done with SARS-CoV-2.

Scientists from Georgetown University (USA) conducted a study, published in Ecology Letters, showing how humans could transmit pathogens to animals far more than previously thought. In fact, the authors found nearly 100 studies describing evidence of direct human-to-animal transmission in wild animals in the wild and in captivity, with published reports dating back to the 1920s.

Disease transmission has recently attracted a lot of attention due to the spread of SARS-CoV-2 in wild white-tailed deer in the United States and Canada. Some data suggests that deer passed the virus back to humans in at least one case – a process known colloquially as overflow–, and many scientists have expressed concern that the new animal reservoirs could give the pathogen the opportunity to evolve into new variants.

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Our study is the first to really explore the extent of this type of contagion beyond covid-19. We found that humans probably transmit their diseases to animals fairly regularly, but we didn’t look hard enough.“, explains Colin J. Carlson, professor at the American institution.

We see many cases of contagion in zoos or in populations of great apes, places where veterinarians closely monitor the animals. But it’s probably a common occurrence, and the fact that we don’t study it carefully enough limits our ability to determine when it will endanger conservation, or potentially our own health, in the future.“, Add.

The good news is that we can probably use information about species biology to predict which animals are at risk for certain diseases, and we’ve shown this with SARS-CoV-2.Carlson continues.

Detect infections early

Anna Fagre, a virologist and wildlife veterinarian at Colorado State University (USA) and another of the authors, explains how we could miss certain transmission events between species, and what this could mean not only for health but also for the status and conservation of infected species.

Long-term monitoring of wild animal populations will allow faster detection of transmission episodes and associated health impacts when they occur”, underlines Fabre, who also published research on the risks of contagion of SARS-CoV-2 using North American deer mice (Peromyscus maniculatus).

For the authors, artificial intelligence can be used to anticipate which species could be at risk of contracting the virus. “This data is used to develop computer models that help us predict which animals can be infected with a certain pathogen, thereby protecting the health of humans and wildlife.“says Fabre.

So when they compared the species that were infected with SARS-CoV-2 with the predictions made by other researchers in the early moments of the pandemic, they found they were able to get it right. most of the time.

Sequencing animal genomes and understanding their immune systems has paid offCarlson points out. “The pandemic has given experts a chance to try out some forecasting tools, and it turns out we’re better prepared than we thought.”.

Monitor two-way transmission

The authors conclude that contagion can be predictable, but the bigger problem is how little we know about diseases in wild animals. “We are monitoring SARS-CoV-2 more closely than any other virus on Earth, so when the comeback happens, we will be able to detect it. However, it is more difficult to assess the risk in other casesCarlson said.

As a result, it will be difficult to assess the severity of the downside risk to human health or wildlife conservation, especially for pathogens other than coronavirus.

Whenever humans and animals come into close contact, whether on farms, in wildlife markets or in zoos, we worry about the diseases they might transmit to us. But you have to look at how they spread in both directions and on a large scale to more accurately assess the risk, as we do with covid-19“says the expert.

The biggest challenge we have is getting enough data to make risk assessment claims. The numbers are quite limited by sampling bias, so we can’t make immediate guesses about which viruses might be a dead end for wildlife and which are a long-term problem. Therefore, we need more information“, he concludes.


Assess the risk of transmission of pathogens from humans to wildlife for conservation and public health“. Ecology Letters


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