Two hippos at Antwerp Zoo have tested positive for the coronavirus, Belgian media reported.
While stressing that Hermien's and Imani's lives do not appear to be in danger, veterinarian Francis Vercammen said they were "expelling snot" which prompted the animal medic to probe further.
The mother, 41, and daughter, 14, have tested positive for COVID amid rising human cases in Belgium and Europe in recent weeks.
Antwerp Zoo tested its animals last year and found no positive cases.
Cats and monkeys get COVID
The infections at Antwerp Zoo are not the first time that zoo animals have tested positive during the pandemic, but most cases are thought to have been among cats and monkeys.
Antwerp Zoo is now closed to the public, and Hermien and Imani have been placed in an isolated social bubble.
The number of infections in Belgium is increasing as winter takes hold. Cases of the new omicron variant have also been detected among citizens.