Four lions have tested positive for COVID-19 at Barcelona Zoo, Spanish authorities said on Tuesday, the second known case in which large felines have contracted the virus.

According to Reuters, the four lions were tested for COVID-19 after keepers noticed they showed slight symptoms of the virus.

Two staff at the facility also tested positive for the virus, authorities confirmed, after the outbreak was first detected last month.

Investigations are currently underway to determine how the lions got infected.

The Veterinary Service of Barcelona contacted colleagues at the Bronx Zoo in New York, where four tigers and three lions tested positive for COVID-19 in April. It is the only other zoo where large felines are known to have contracted the virus.

"The Zoo has contacted and collaborated with international experts such as the Veterinary Service of the Bronx Zoo, the only one that has documented cases of Sars-CoV-2 infection in felines," Reuters quotes the Barcelona Zoo.

"The lions were given veterinary care for their mild clinical condition - similar to a very mild flu condition - through anti-inflammatory treatment and close monitoring, and the animals responded well."