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SAN DIEGO — 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 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 Zoo Global said in a press release. The U.S. Department of Agriculture National Veterinary Services Laboratories confirmed the positive results on Monday.

It is believed the gorillas caught the infection from an asymptomatic staff member, despite following precautions and wearing PPE when near the primates, the organization said. It’s still not known whether the animals will have a serious reaction.

“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.”

Gov. Gavin Newsom addressed the positive tests 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 adjudication of the facts, but nonetheless, this has been area that’s long been of concern human to animal transmission. But our beloved gorillas – we are obviously concerned about.”