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SAN DIEGO (KSWB) — Two gorillas at the San Diego Zoo Safari Park have tested positive for COVID-19 — the first known instance of the virus being naturally transmitted to great apes.

The gorillas underwent testing for COVID-19 after they started coughing Wednesday, and results from the preliminary test came back positive on Friday, San Diego Global said in a press release. The U.S. Department of Agriculture National Veterinary Services Laboratories confirmed the positive results Monday.

It is believed the gorillas caught the infection from an asymptomatic staff member despite the employee following precautions and wearing PPE when near the primates, the organization said.

The park closed to visitors Dec. 6 in accordance with the state’s efforts to curb COVID-19 transmission amid an explosion in new cases that has strained California hospitals.

“Aside from some congestion and coughing, the gorillas are doing well,” said Lisa Peterson, executive director of the San Diego Zoo Safari Park. “The troop remains quarantined together and are eating and drinking. We are hopeful for a full recovery.”

There has been concern over how COVID-19 would affect the endangered animals, who share 98 percent of their DNA with humans. Like humans, gorillas are social creatures and a deadly virus could spread quickly through their communities.

Gov. Gavin Newsom addressed the positive test in a news conference.

“We have two gorillas at the San Diego Zoo that now have tested positive for COVID-19. Two that have tested positive – we have another that is symptomatic. We are currently confirming the source of the infection and the strain. There is some question did it come human to animal? That’s being determined and one has to respect that process and the a adjudication of the facts, but none the less, this has been area that’s long been of concern human to animal transmission. But our beloved gorillas – we are obviously concerned about.”

On Monday, the zoo instituted new safety precautions for staff, including face shields and eye goggles that will be mandatory when working in contact with the animals.