Four lions at Barcelona Zoo, three of them older females, caught COVID-19 last month but suffered only mild symptoms and have since recovered, the Catalan animal park said.

Their keepers were tipped off when they noticed "mild respiratory symptoms" among three 16-year-old females and a four-year-old male, a zoo statement said.

The symptoms emerged as two of their keepers tested positive for the virus.

"The four lions were tested with the viral antigen detection kit... and were found to be positive," it said, indicating the diagnosis was confirmed by PCR tests.

They were immediately treated with anti-inflammatories and closely monitored under a protocol similar to that for the flu, and "responded positively."

"At no time were the lions seen having difficultly breathing or other respiratory issues, and all symptoms disappeared within a fortnight, apart from coughing and sneezing," the zoo said.

To avoid catching the virus, the keepers wore FFP3 masks, plexiglass visors and protective footwear, and they were lowered into the enclosure in a halter.

The zoo also contacted "international experts such as the Bronx Zoo veterinary service in New York, the only one to have documented a case of Sars-CoV-2 infection in big cats," it said.

In early April, a four-year-old female tiger at the Bronx Zoo tested positive for COVID-19, likely contracting it from a keeper who was asymptomatic at the time.

Since the start of the pandemic, cats, dogs and various other animals have tested positive for COVID-19 but until now, minks are the only animals proven to both contract the virus and pass it on to humans.

Several countries have ordered the mass culling of their mink populations, notably Denmark where more than 10 million have already been killed.