Some of the deadliest diseases to humanity have transferred from animals to humans. For example, the virus that causes acquired immunodeficiency syndrome (AIDS) came to humans from chimpanzees. Many experts believe that the virus responsible for the COVID-19 pandemic was transmitted to humans from bats. However, a new study has shown that this transmission is not one-directional. Analysis of available viral genome sequences has led to a surprising conclusion: humans transmit viruses to animals at nearly the same rate that animals transmit viruses to humans.
Researchers examined about 12 million viral genomes and found approximately three thousand instances of viruses transferring from one species to another. Among these cases, 79 percent involved viruses transferring from one animal species to another, while the remaining 21 percent involved humans. Of these cases, 64 percent represented transmission from humans to animals, known as anthroponotic diseases, while 36 percent involved transmission from animals to humans, called zoonotic diseases.
The animals affected by anthroponotic diseases included pets such as cats and dogs, domesticated animals like pigs, horses, and cattle, birds like chickens and ducks, primates such as chimpanzees, gorillas, and various monkey species, as well as other wildlife like raccoons, black marmosets, and African soft-furred mice. Wild animals, in particular, were more susceptible to infection transmissions from humans compared to the other way around.
Cedric Tan, a PhD student in computational biology at the Genetics Institute of University College London and the lead author of the study published this week in the journal Nature Ecology & Evolution, stated, "This really highlights our huge impact on the environment and the animals around us."
Humans and animals are hosts to countless microbes that can transmit to other species through close contact. The study examined viral transmission processes involving all vertebrate groups, including mammals, birds, reptiles, amphibians, and fish. Over thousands of years, epidemics that have claimed millions of lives have stemmed from pathogens like viruses, bacteria, and fungi that transmitted to humans from animals. Zoonotic diseases remain a major concern regarding emerging infectious diseases.
