Several gorillas at Zoo Atlanta have tested positive for COVID-19 after handlers noticed many of the great apes were showing signs of mild coughing, runny noses and loss of appetite.

Zoo Atlanta’s animal handlers collected faecal samples and nasal and oral swabs from the gorillas and sent the samples to a diagnostic lab at the University of Georgia, which returned presumptive positive results for the virus that causes Covid-19, an AP report cited a Zoo Atlanta statement as saying.

The statement didn’t mention the number of gorillas that were infected, but the Atlanta Journal-Constitution reported 13 gorillas had tested positive for the virus.

The zoo statement said its teams are collecting samples for testing from the zoo’s entire gorilla population, which numbers 20 members living in four troops. The Atlanta Journal-Constitution report said members from each of the four troops showed evidence of infection.

The newspaper report said it is likely that the virus made its way into the gorilla population from an animal care staffer who was asymptomatic upon coming to work, but who later tested positive for the virus.