Tigers at resort in Dong Nai province died after being fed sick chicken, additional deaths reported in other locations.
Dozens of tigers, three lions and a panther have died in zoos in southern Vietnam, with subsequent tests detecting cases of bird flu.
The country’s Ministry of Health said in a statement on Thursday that two samples taken from dead tigers at Mango Garden Resort in Dong Nai province tested positive for the H5N1 strain of bird flu.
Since early last month, 20 tigers died at the resort after being fed chicken, said Phan Van Phuc, an official of Dong Nai province’s Centre for Disease Control, in the statement.
“It’s likely that the tigers had been infected from sick chicken, and the authorities are tracking the source of the chicken to determine the cause,” said Phan.
State media had previously said a total of 47 tigers, three lions and a panther died at the private My Quynh safari park in Long An province and the Vuon Xoai zoo in Dong Nai, near Ho Chi Minh City, in August and September.
The animals died “because of H5N1 type A virus”, according to test results from the National Centre for Animal Health Diagnosis reported by the official Vietnam News Agency (VNA) on Wednesday.
No zoo staff members in contact with the animals had experienced respiratory symptoms, the VNA report added.
Education for Nature Vietnam (ENV), an NGO focused on wildlife conservation, said there were 385 tigers living in captivity in Vietnam at the end of 2023.
About 310 are kept at 16 privately owned farms and zoos, while the rest are in state-owned facilities.
The World Health Organisation (WHO) says that since 2022, there have been increasing reports of deadly outbreaks among mammals caused by influenza viruses, including H5N1.
The organisation says H5N1 infections can range from mild to severe in humans, and in some cases can be fatal.
Vietnam notified the WHO about a human death from the virus in March.
In Thailand, dozens of tigers died from bird flu or were culled at the world’s largest breeding farm in 2004.