STOCKHOLM - A tiger has been put to sleep at a Swedish zoo after it fell ill with the coronavirus, national public television SVT reported on Tuesday.

Two lions at the same zoo have also been confirmed infected, while more animals have displayed symptoms.

The assumption is the animals at Boras Zoo in southwestern Sweden were infected by employees, as several of the zookeepers have had COVID-19 symptoms and three have been tested positive for the virus, the report said.

The 17-year-old female Siberian tiger Nastasja was euthanized when she lost her appetite and her condition deteriorated.

On Jan 13, Swedish National Veterinary Institute discovered Nastasja was infected by COVID-19. A male tiger kept in the same enclosure has also displayed mild symptoms.

A group of lions kept in the same building have also displayed signs of mild infection, and the virus has been confirmed in two cases.

"This is the first known case of (COVID infected) felines in Sweden," Karl Stahl, a veterinary epidemiologist at the veterinary institute, told SVT News.

The assumption the cats at Boras Zoo were infected by humans and not the other way around is based on the fact that there are no reports of felines infecting humans, Stahl said.

Cases of big cats infected with COVID-19 have previously been reported from other countries.

In April, a tiger at Bronx Zoo in New York was confirmed to be infected with the virus but has since recovered. Another tiger at Woodland Park Zoo in Seattle has also made a full recovery.

A puma in South Africa and a gorilla at a California zoo are among other animals that have tested positive for the virus, according to the US Centers for Disease Control and Prevention.

Meanwhile, a small number of pet cats and dogs have been reported to be infected in several countries and regions.