Some of the deadliest diseases to stalk humankind have come from pathogens that jumped from animals to people. The virus that causes AIDS, for example, crossed over from chimpanzees. And many experts believe the virus that caused the COVID-19 pandemic flowed from bats.

But, as a new study shows, this exchange has not been a one-way street. An analysis of all the publicly available viral genome sequences yielded a surprising result: humans give more viruses — about twice as many — to animals than they give to us.

The researchers looked at nearly 12 million virus genomes and detected almost 3,000 instances of viruses jumping from one species to another. Of those, 79% involved a virus going from one animal species to another animal species. The remaining 21% involved humans. Of those, 64% were human-to-animal transmissions, known as anthroponosis, and 36% were animal-to-human transmissions, called zoonosis.