At least two gorillas at California’s San Diego Zoo have caught the coronavirus, the first known instance of natural transmission to great apes, officials said Monday.

Two primates began coughing last week and have since tested positive for Covid-19, while a third is showing symptoms, Governor Gavin Newsom said.

They are thought to have contracted the virus from an asymptomatic zoo worker, though this has yet to be confirmed.

“Aside
from some congestion and coughing, the gorillas are doing well,” the
world-famous zoo’s executive director Lisa Peterson said in a statement.

“The troop remains quarantined together and are eating and drinking. We are hopeful for a full recovery.”

Gorillas share up to 98 percent of their DNA with humans, and studies have found that some non-human primates are susceptible to Covid-19 infection.

It
is not yet known if the gorillas will have a serious reaction to the
disease that has killed 1.94 million humans, or if other troop members
have also been infected.

The San Diego Zoo Safari Park, where the
gorillas are kept, has been closed to visitors since early December as
record cases began surging through Southern California.

Workers are all required to wear personal protective equipment such as masks when near the gorillas, the zoo said.