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Humans infect animals with diseases much more than we thought

"The biggest worry is how little we know about wildlife disease."

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By Jim Leffman via SWNS

Humans have transmitted viruses to animals at least 100 times in a reversal of killers such as COVID-19 and Ebola, scientists believe.

Researchers think that humans have passed diseases back to animals far more often than previously believed.

The team from Georgetown University Medical Centre found nearly 100 different cases of disease “spillback” from humans to wild animals.


One good example was the way in which COVID-19 has been able to spread in mink farms, lions and tigers in zoos and wild white-tailed deer.

The study, published in the journal Ecology Letters found nearly half the incidents happened in captive settings like zoos and more than half involved our close relatives, primates.

Dr. Gregory Albery, the study’s senior author, said: "There has understandably been an enormous amount of interest in human-to-wild animal pathogen transmission in light of the pandemic.

“To help guide conversations and policy surrounding spillback of our pathogens in the future, we went digging through the literature to see how the process has manifested in the past.”

A selective focus shot of a lion from his side profile in the cage
In October 2021 Denver Zoo reported that 11 of their African lions had tested positive for COVID-19. (Oakland Images/Shutterstock)

The researchers say unsurprisingly most of the cases were in animals that for one reason or another came into close contact with humans.

Another lead author, Dr. Anna Fagre, virologist and wildlife veterinarian at Colorado State University, said: “This supports the idea that we’re more likely to detect pathogens in the places we spend a lot of time and effort looking, with a disproportionate number of studies focusing on charismatic animals at zoos or in close proximity to humans.

“It brings into question which cross-species transmission events we may be missing, and what this might mean not only for public health but for the health and conservation of the species being infected.”

Disease spillback has recently attracted attention due to the spread of SARS-CoV-2, the virus that causes COVID-19, in wild white-tailed deer in the United States and Canada.

Some data suggests that deer have given the virus back to humans in at least one case, and many scientists have expressed broader concerns that new animal reservoirs might give the virus extra chances to evolve new variants.

However, using artificial intelligence, the researchers compared species that have been infected with SARS-CoV-2 to predictions made by other researchers earlier in the pandemic.

They found on the whole that scientists were able to guess correctly.

Research Professor Colin Carlson from the Global Health Science and Security at Georgetown University added: “The pandemic gave scientists a chance to test out some predictive tools, and it turns out we’re more prepared than we thought.

“It’s quite satisfying to see that sequencing animal genomes and understanding their immune systems has paid off."

However whilst spillover can be predicted, the biggest worry is how little we know about wildlife disease.

Prof Carlson added: "We're watching SARS-CoV-2 more closely than any other virus on earth, so when spillback happens, we can catch it."

"It's still much harder to credibly assess risk in other cases where we're not able to operate with as much information.”

Dr. Fagre commented: “Long-term monitoring helps us establish baselines for wildlife health and disease prevalence, laying important groundwork for future studies.

“If we’re watching closely, we can spot these cross-species transmission events much faster, and act accordingly.”

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