This article originally appeared on VICE US.
When five tigers and three lions tested positive at the Bronx Zoo this month, they became the world’s first wild animals known to have contracted the coronavirus from humans.
Scientists hope they’re also the last.
“We likely got this from an animal, but now we are putting at risk the entire ecosystem on our planet,” said Arinjay Banerjee, a virologist at McMaster University.
Researchers were confident as early as January that the coronavirus that causes COVID-19 was zoonotic, or spreads from animals to humans. It took longer to confirm that the virus goes the other way, too.
SARS-CoV-2, the virus that causes COVID-19, infects certain animals more than others: Ferrets, hamsters, and primates are all susceptible. But the virus replicates poorly in dogs, pigs, ducks, and chickens, according to a study in Science. A handful of pet cats and dogs have also tested positive around the world, but they didn’t get very sick. Testing is in its early stages, so it’s unclear which other animal groups could be affected.
Wildlife managers around the world have ramped up protections for fragile populations like India’s tigers and great apes. Scientists in the U.S. are particularly concerned about animals that are already vulnerable to diseases, like bats and endangered black-footed ferrets. Since scientists believe a Chinese bat species is the source of the coronavirus, they’re concerned North American bats could also become carriers.
There’s no evidence that animals have given the virus back to people since the pandemic started. But if humans do spread the coronavirus to wildlife, it will become much harder to eradicate.
“Once it's in wildlife, it's very hard to get rid of it,” said Dr. William Karesh, EcoHealth Alliance’s executive vice president for health and policy. “It's like opening Pandora's box.”