Two gorillas as the San Diego Zoo Safari Park have tested positive for SARS-CoV-2, the first reported cases of COVID-19 in great apes.

Both apes are experiencing congestion and cough but “are doing well,” according to the zoo’s executive director Lisa Peterson. The Zoo suspects the gorillas acquired the infection from an asymptomatic staff member, despite following all recommended CDC precautions. “The troop remains quarantined together and are eating and drinking. We are hopeful for a full recovery.”

The Zoo reported that two of the gorillas began coughing on Jan 6 and preliminary tests on Jan 8 detected the presence of the virus in the gorilla troop. The US Department of Agriculture (USDA) National Veterinary Services Laboratories (NVSL) confirmed the positive results on Jan 11.

The test results confirm the presence of SARS-CoV-2 in some of the gorillas and does not definitively rule out the presence of the virus in other members of the troop.

“Research studies have verified that some non-human primates are susceptible to infection with SARS-CoV-2, but this is the first known instance of natural transmission to great apes and it is unknown if they will have any serious reaction,” the Zoo said in a press release.

The San Diego Zoo Safari Park has been closed to the public since December 6.