In a surprising turn of events, a recent study has found that humans transmit more viruses to animals than animals do to humans. The research, published in the journal Nature Ecology & Evolution, analyzed nearly 12 million viral genomes and uncovered almost 3,000 instances of viruses jumping between species.
While zoonosis—animal-to-human transmission—has been a significant concern due to diseases like AIDS and COVID-19, this study highlights that anthroponosis, or human-to-animal transmission, occurs even more frequently. Of the transmissions involving humans, 64 percent were from humans to animals, affecting a wide range of species from pets and livestock to wildlife.
“This really highlights our enormous impact on the environment and the animals around us,” said Cedric Tan, lead author of the study and a doctoral student in computational biology at University College London’s Genetics Institute. “Viruses can jump between different species via the same modes of transmission that apply to humans, including direct contact with infected fluids or through bites.”
The affected animals include domestic pets like cats and dogs, farm animals such as pigs, horses, and cattle, and wild creatures including primates, raccoons, and various bird species. Wild animals, in particular, were more likely to experience virus transmission from humans than the other way around.
Co-author Francois Balloux, director of the UCL Genetics Institute, emphasized the significance of the findings. “The vast majority of pathogens circulating in humans have been acquired from animals at some point in time,” he said. “The main reason recent host jumps can be so devastating is because the population of host species has no pre-existing immunity to the novel disease.”
Historically, some of the deadliest pandemics, such as the 14th-century Black Death and present-day threats like the Ebola virus, originated from animals. The study sheds light on the often-overlooked reverse transmission, which may have implications for wildlife conservation and the emergence of new diseases.
“In most cases, such infections lead nowhere, as the virus is poorly adapted and there is no onward transmission in the new host,” Balloux explained. “But in some cases, the virus can start circulating, causing a disease outbreak, an epidemic, a pandemic, or even establish itself as an endemic pathogen.”
The researchers stress the importance of monitoring human-to-animal viral transmissions, which could have unforeseen consequences on biodiversity and animal health. As human activities increasingly encroach upon natural habitats, the potential for cross-species virus transmission may rise.
“Our study underscores the interconnectedness of human and animal health,” Tan concluded. “Understanding the dynamics of virus transmission between species is crucial for developing strategies to prevent future pandemics and protect both human and animal populations.”
Asia, with its diverse ecosystems and rapidly expanding urban areas, is a region where human-animal interactions are particularly profound. The findings of this study are especially relevant here, where the balance between wildlife conservation and human activities is delicate.
Reference(s):
Humans give more viruses to animals than they give us: study
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