Several gorillas at the San Diego Zoo are believed to have contracted coronavirus, in what is believed to be the first cases among captive primates.
Two have tested positive for COVID-19 after falling ill, and a third gorilla appears to be symptomatic, California governor Gavin Newsom said on Monday.
The zoo's executive director, Lisa Peterson, told The Associated Press on Monday that eight gorillas that live together are thought to have the virus and several more have been coughing.
The infection is believed to have come from an asymptomatic staff member, who later tested positive, despite there being extensive coronavirus measures in place to protect the apes.
"Aside from some congestion and coughing, the gorillas are doing well," Ms Peterson said.
"The troop remains quarantined together and are eating and drinking. We are hopeful for a full recovery."
She added: "For almost one year our team members have been working tirelessly, with the utmost determination to protect each other and the wildlife in our care from this highly contagious virus.
"The safety of our staff and the wildlife in our care remains our number one priority."
The safari park tested the gorillas using their faecal matter, after two of the animals began coughing on 6 January.
Veterinarians are closely monitoring the group. They are being given vitamins, fluids, and food but no specific treatment for the virus.
While other wildlife has contracted COVID-19, including minks and tigers, the gorilla cases are believed to be the first reported from a zoo in the United States and possibly the world.
Studies have shown that some primates are susceptible to infection with the virus, although it is unknown if they will have a serious reaction.
Zoo officials are working closely with experts who have been treating humans with coronavirus in case the apes deteriorate.
"This is wildlife, and they have their own resiliency and can heal differently than we do," Ms Peterson said, adding that for now the focus is to keep them "healthy and thriving".