DENVER (KDVR) — The Denver Zoo announced Monday that 11 African lions, ranging in age from 1 to 9 years old, have tested positive for COVID-19.

The zoo said animal care and veterinarians describe the symptoms as being relatively mild at this point, and they are closely monitoring and treating the lions individually as needed.

Zookeepers noticed the lions were coughing, sneezing, acting lethargic and battling nasal discharge. The lions tested positive after nasal swab samples were sent to Colorado State University’s Veterinary Diagnostic Laboratory. The positive cases were confirmed by the U.S. Department of Agriculture’s Veterinary Services Laboratories, the Denver Zoo said Monday.

“There have been a number of big cats to come down with COVID-19 at zoos throughout the country, including our two tigers, Yuri and Nikita,” said Brian Aucone, senior vice president for life sciences at the zoo. “Fortunately, the vast majority have fully recovered, and the upside is that there’s an established knowledge base for us to draw from to help treat our animals. We’ve been in touch with other zoos that have also recently managed COVID cases in their big cats to inform the care we’re providing.”

Earlier this month, two of Denver Zoo’s Amur tigers tested positive for COVID-19. The zoo said the African lions started showing symptoms after the tigers tested positive. It is unclear if the two groups of positive cases are connected.

The zoo said the animal care staff adheres to strict COVID-19 protocols around our animals, including required use of personal protective equipment, hygiene, cleaning, employee self-screening and health management.

None of the lions were vaccinated against COVID-19, according to the zoo.

“Our veterinarians are planning to vaccinate them along with the tigers as soon as more doses of the animal-specific Zoetis vaccine become available,” the zoo said.

Zoos across the country are trying to protect their animals as cases of COVID-19 continue to crop up. Three African lions at the Indianapolis Zoo tested positive last week after two females started showing symptoms. The third, a male lion, was asymptomatic.

Indianapolis Zoo veterinarians have administered at least the first shot of the COVID-19 vaccine to the animals that are susceptible to the virus, including lions, tigers, cheetahs and apes.