Experts identify 100 cases of humans passing disease to animals

The pandemic has created interest among the scientific community to better understand human-to-wild animal disease transmission. An international research team led by scientists at Georgetown University has found that humans give viruses back to animals more often than expected.

The study describes nearly 100 different cases where diseases have undergone “spillback” from humans back into wild animals. This has been seen most recently with SARS-CoV-2 (COVID-19) spreading in mink farms, zoo lions and tigers, and among white-tailed deer in the wild.

The researchers found that almost half of these cases took place in captive settings like zoos, where veterinarians keep a close eye on animals and are more likely to notice changes in health. Interestingly, more than half of the overall cases were human-to-primate transmission. This is likely because it is easier for pathogens to jump between closely-related hosts, and because endangered great ape populations are carefully monitored.

“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,” said study lead author Dr. Anna Fagre. “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.”

In Canada and the United States, disease spillback has attracted attention due to the spread of COVID-19 in white tailed deer. Some data suggests that deer have given the virus back to humans in at least one case. This has raised concern amongst scientists and suggests that animal reservoirs might create opportunities for the virus to evolve into new variants.

The study also sheds light on some good news, as it found that artificial intelligence can be used to help anticipate the species at risk of contracting the virus. ”The pandemic gave scientists a chance to test out some predictive tools, and it turns out we’re more prepared than we thought.”  said study co-author Dr. Colin Carlson.

The research is part of a National Science Foundation-funded project called the Viral Emergence Research Initiative, or Verena. The Verena team uses machine learning to study the science of the host-virus network. This is a new field that provides critical insights for scientists to understand how and why humans share diseases with animals.

While new technology can help predict spillover, there is still so little we understand about wildlife disease, creating opportunity for continuous research. 

“Long-term monitoring helps us establish baselines for wildlife health and disease prevalence, laying important groundwork for future studies,” said Dr. Fagre. “If we’re watching closely, we can spot these cross-species transmission events much faster, and act accordingly.”

The study is published in the journal Ecology Letters.

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By Katherine Bucko, Earth.com Staff Writer