PORTLAND, Ore. — The staff of Oregon Zoo say that they are mourning after the sudden loss of their youngest Asian elephant, Lily. The little elephant died after the sudden emergence of a viral infection that claimed her less than one day later.

Lily would have been six years old on Friday, the day following her death on Thursday night.

"Veterinary and care staff did all they could to save her, and Lily fought hard to the end," Oregon Zoo said in a post. "When she passed, she was with her mother Rose-Tu and surrounded by people who had cared for her since her birth. Her aunties Chendra and Shine also spent time beside her. Lily brought joy to everyone she encountered. This is a heartbreaking loss for the herd and our entire community."

The zoo said that Lily suffered from a disease called elephant endotheliotropic herpesvirus (EEHV) — a virus known to be carried by most Asian elephants that can become active in a few without much warning.

"Often, it remains latent, causing mild or no symptoms, but for reasons unknown it can sometimes come out of latency and cause disease. Once the disease becomes active in calves, it is usually fatal, often causing death within few days even with intensive treatment," Oregon Zoo said.

The disease affects both wild elephants and those in captivity, but there is much about the disease and how it strikes that is not well understood.

"It's very difficult to study the virus in wild elephants," said Dr. Don Moore, zoo director. "But zoos can monitor their elephant herds closely and obtain samples of blood and other fluids. Right now, that's our best hope of developing a vaccine."

Oregon Zoo closed their gates on Friday and plan to remain closed for the remainder of the day — intending to reopen on Saturday.