The Denver Zoo in the United States announced this Saturday that two hyenas have tested positive for Covid-19, the first confirmed cases among these animals worldwide.

According to the National Veterinary Services Laboratories (NVSL), the conclusion comes after tests were done on several lions that became ill. In addition to the two hyenas, 11 lions and two tigers at the zoo were confirmed to be infected.

"Hyenas are strong and resilient animals and are known to be highly tolerant of anthrax, rabies and esgana. They are healthy and should make a full recovery," the zoo said in a statement, quoted by the Guardian.

Explained by zoo officials, some animals, such as 22-year-old Ngozi and 23-year-old Kibo, had mild symptoms, including fatigue, coughing, and nasal secretions. The remaining animals that tested positive for Covid-19 have fully recovered or are almost recovered.

"We now know that many other species may be susceptible to Covid-19, based on multiple reports, and we continue to use the highest level of care and caution when working with all of our 3,000 animals and 450 different species," the zoo said.

The cases that have been reported in various species around the world are essentially cases that have been in close proximity to infected people, says the US Department of Agriculture. Even so, scientists are still working to understand how these infections develop in animals. However, based on the information they have, the risk of passing the virus to humans is low.