Officials from a Belgian zoo said Friday that a pair of hippopotamuses in its care are in isolation after testing positive for COVID-19, possibly the first time ever such animals have caught the disease.

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Belgium’s national veterinary lab has confirmed that Antwerp Zoo’s two hippos — Imani, 14, and 41-year-old Hermien — contracted COVID-19. It's unclear how they caught it. Both the giant semiaquatic herbivores are well, apart from exceptionally runny noses. Keepers have tightened virus restrictions around the zoo.

"To my knowledge, it’s the first recorded contamination among this species. Throughout the world this virus has mostly been seen in great apes and felines," Antwerp Zoo vet Francis Vercammen said.

LULIMIBI, EASTERN DRC - JULY 31: Recovering hippo populations close to the ICCN Ranger station on July 31, 2013 in Lulimibi, Lake Edward. Lake Edward once housed the largest hippo population in the world, a figure decimated by conflict since 1994. Hippo meat formed a staple of the diet of armies and militias alike, reducing the population to a figure close to 600 of what was once over 30 000. Lulimibi is in the 'Block V' area of Virunga National Park. UK company Soco International PLC is planning to explore for oil in DRC's Virunga National Park, a protected World Heritage Site and most biodiverse park in Africa. (Photo by Brent Stirton/Getty Images for WWF-Canon)

Recovering hippo populations close to the ICCN Ranger station on July 31, 2013 in Lulimibi, Lake Edward. (Photo by Brent Stirton/Getty Images for WWF-Canon) (2013 Getty Images)

How the hippos got the disease remains a mystery. All the zoo’s animals were tested for COVID-19 last year and no case was found. Hippos' noses normally tend to be wet, but Vercammen said he decided to test the thick liquid coming out as a precaution and was surprised by the result.

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The hippos’ enclosure has been closed to visitors and will only be reopened once the pair test negative. 

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Their handlers have all tested negative for the virus and must wear masks and safety glasses and disinfect their footwear before approaching the two animals.