The Denver Zoo says two of its hyenas have COVID-19.

They are the first two hyenas in the world known to have contracted the virus, the zoo said.

Zoo officials say the hyenas are experiencing "extremely mild symptoms."

"They have maintained normal energy levels, and interaction with enrichment and their keepers," the zoo said. "Hyenas are famously tough, resilient animals that are known to be highly tolerant to anthrax, rabies and distemper."

The zoo expects the hyenas to make a full recovery.

The hyenas are not the first animals at the zoo to test positive for COVID-19. Eleven lions and two tigers have also tested positive for the virus.