Three snow leopards, two males and a female, tested positive for the virus at the Louisville Zoo, the zoo and the US Department of Agriculture's Animal and Plant Health Inspection Service confirmed Friday.

The leopards were likely infected by an asymptomatic staff member "despite precautions taken by the zoo," the USDA's Animal and Plant Health Inspect Service said.

The snow leopards are one of at least six animal species to become infected with coronavirus after close contact with humans. The first was a Malayan tiger at the Bronx Zoo, who in April tested positive for coronavirus after showing symptoms of respiratory illness. By the end of the month, eight of the zoo's big cats, including four other tigers and three African lions, tested positive for the virus.