(CNN)Two hippos at a zoo in Antwerp, Belgium, have tested positive for Covid-19, in what is believed to be the first such infection reported in the species.
The hippos, named Imani and Hermien, have shown no symptoms "other than runny noses," according to a news release from the zoo.
How the animals were exposed to the virus is unknown -- their caretakers have not shown any Covid-19 symptoms and all tested negative for the virus, the release said.
Imani, who is 14 years old, and Hermien, who is 41, are being kept in isolation for now and cannot be seen by visitors, the zoo said.
"To my knowledge, this is the first known contamination in this species. Globally, this virus has mostly been reported in great apes and felines," said the zoo's veterinarian Francis Vercammen, who oversaw their testing for the coronavirus.
Covid-19 infections in zoo animals and pets have been reported around the world, including in big cats, primates, ferrets and minks, according to the US Centers for Disease Control and Prevention. Last month, three snow leopards at a zoo in Nebraska died of complications from the virus.
Companion animals, especially cats and dogs, are the leading group of animal species impacted by coronavirus. While animal-to-human transmission risk is low, people can spread coronavirus to pets, CDC officials have warned.