KANSAS CITY, Mo. — The Kansas City Zoo says one of its Western lowland gorillas tested positive for the delta variant of COVID-19.

The zoo presumes the other five gorillas are also positive for the virus, but are waiting on test results for confirmation.

Zookeepers said all six of the gorillas have shown COVID-19 symptoms, but some have already returned to normal. The zoo said others are still responding to treatment and their conditions are improving.

The animals’ care specialist first reported a gorilla named Charlie did not appear well on Sept. 22. The animal began coughing three days later, according to the zoo.

The veterinary health team started treating the animals immediately, but within 72 hours, additional gorillas started to develop symptoms. The zoo treated all of the gorillas with medications including expectorants, Vitamin C, Zinc, and ibuprofen.

All of the great apes at the zoo will receive the COVID-19 vaccine made by Zoetis as soon as it receives its shipment. Animal experts said the Zoetis vaccine was specifically developed for use with animals and research shows it is safe.

The zoo said it doesn’t know exactly how the gorillas were infected, but has worked to minimize the risk to animals, staff and visitors.