A lion that tested positive for the coronavirus at an Indiana zoo has — most likely — transmitted the virus to at least two of its keepers, according to new research.

It has been known for a long time that the virus that causes Covid-19 can infect many species and that it can be transferred from human to animal. However, “animal-to-human transmission of the virus has not previously been reported in a zoo setting,” the researchers note.

The African lion, aged around 20 years, was diagnosed positive for the coronavirus in December 2021 when he developed a cough and difficulty breathing. The ten caregivers, who were in close contact with the sick feline, were immediately tested, but all tests came back negative. A week later, however, three of the caregivers tested positive, even though they had not been in contact with human cases.

The lion was elderly and suffered from kidney disease and spinal degeneration, so his caretakers had to hand-feed him. Researchers suspect the lion contracted the virus from an asymptomatic zoo human.