The Oregon Zoo’s youngest elephant has died after the sudden onset of a dangerous and swift-moving virus.

Zoo officials say Lily, a 6-year-old Asian elephant, died just a day after routine blood samples showed the virus in her system. The elephant did not show obvious signs of the virus before the blood samples came back positive.

Veterinarians treated her with fluids, antiviral medicine and a transfusion. Vets believe the virus, commonly known as EEHV, is present in almost all Asian elephants. They’re not sure why the disease sometimes comes out of latency. The virus is usually fatal in calves once it becomes active.

The zoo will remain closed Friday, including during the scheduled evening ZooLights.