Twenty big cats - including a Bengal tiger and four cougars - have died of bird flu over the past several weeks at an animal sanctuary in the state of Washington.

"This tragedy has deeply affected our team, and we are all grieving the loss of these incredible animals," the Wild Felid Advocacy Center of Washington wrote in a post on Facebook.

The devastating viral infection, carried by wild birds, spreads primarily through respiratory secretions and bird-to-bird contact and can also be contracted by mammals that ingest birds or other products.

The sanctuary is under quarantine and is closed to the public to prevent the spread of the virus, the statement said.

The animals died between late November and mid-December, the sanctuary's director, Mark Mathews, told the New York Times.

"We've never had anything like it; they usually die basically of old age," he said. "Not something like this, it's a pretty wicked virus."

The news comes as bird flu continues to spread among cattle and poultry in the US, while also severely infecting at least one human.

The sanctuary said it had lost five African serval cats, four bobcats, two Canada lynx and a Bengal tiger, among others. Only 17 cats now remain at the Center.

"Cats are particularly vulnerable to this virus, which can cause subtle initial symptoms but progress rapidly, often resulting in death within 24 hours due to pneumonia-like conditions," the sanctuary said in its Facebook statement on Friday.

Bird flu has long infected poultry flocks in the US. But the virus began to infect cattle in the US for the first time in March.

And since April 2024, there have been a total of 61 human cases of bird flu reported in the US, according to the Centers for Disease Control and Prevention.

The CDC says that the risk to the general public remains low, and there has been no sustained human-to-human transmission.

Most have reported mild symptoms, though one person was taken to the hospital with a severe case of bird flu in Louisiana this month.

Last week, California Governor Gavin Newsom declared an emergency over the outbreak among the state's dairy cows to help the government have the "resources and flexibility they need to respond quickly to this outbreak".