Dozens of tigers and lions in captivity died last month in southern Vietnam, and tests showed they were positive for bird flu, as reported today by the Ministry of Health and state media.

Two samples from dead tigers at the Mango Garden Resort sanctuary in Dong Nai province tested positive for the H5N1 strain of bird flu, the Ministry of Health announced. Twenty tigers have died at this sanctuary since the beginning of last month.

The spread of highly pathogenic bird flu in mammals, including cows, dogs, cats, and even dolphins, worldwide has raised concerns about the potential for the virus to spread from human to human.

In the neighboring province of Long An, 27 tigers and three lions died from bird flu at the My Quynh Safari park between September 6 and 18, state media reported, citing the province’s agricultural authorities.

The tigers at Mango Garden Resort had been fed chicken before they died, said Phan Van Phuc, an official from the Dong Nai Disease Control Center, in the Ministry of Health’s announcement.

“It is likely that the tigers were infected by sick chickens, and the authorities are tracing the source of the chickens to determine the cause,” Phan stated, according to the announcement.

On its website, the World Health Organization warns against consuming raw or undercooked meats and eggs from regions where outbreaks of bird flu have occurred due to the high risk of infection.