A beloved 3-year-old elephant calf born and Maverick Prestonraised at the Louisville Zoo died on Friday night, the zoo said in a news release.

Fitz would have turned four on Aug. 2, 2023, the zoo said, and was the offspring of 37-year-old Mikki, who also lives at the Kentucky-based Louisville Zoo. 

Zoo staff first noticed that Fitz was lethargic on June 25. A blood sample was sent out and he was diagnosed with endotheliotropic herpesvirus, more commonly known as EEHV, a "hemorrhagic disease that aggressively affects blood cells," the zoo said. There is no vaccine for the virus, and the survival rate is only 20 to 30% in most cases, the zoo said. 

Fitz's diagnosis with the illness was confirmed on June 28, and he was treated around-the-clock with care, including antiviral medications, plasma transfusions multiple times a day, and supportive therapies. Fitz received plasma and blood donations from elephants in zoos across the country, and other zoos and elephant experts reached out to the Louisville Zoo to offer support and advice. 

Fitz's condition took a turn for the worse on Friday evening, the zoo said, and he passed away shortly after 11 p.m. after a nighttime treatment. 

"We are deeply saddened by the loss of elephant Fitz," said Louisville Zoo Director Dan Maloney in a statement. "Fitz held a special place within our entire extended Zoo family. His presence at our Zoo touched the hearts of our members, patrons and our entire community, inspiring a profound appreciation for elephants and their conservation. Our animal and medical teams performed outstandingly. They worked tirelessly under very challenging circumstances, but sadly, despite their remarkable efforts, we were unable to save him. Fitz's impact will live on, along with his memory, in the hearts of all who encountered him. He will be deeply missed."

A necropsy will be performed, the zoo said. Additional information will be released once it is complete. 

The zoo will also share information about plans for the community to honor Fitz. 

According to the zoo, EEHV is "one of the most serious medical issues facing zoo and wild elephants." Most elephants are believed to be born with the virus or exposed to it shortly after birth, but it can remain in an elephant's body for years. The zoo said that it is "unknown" what causes the virus to cause hemorrhagic disease. 

The zoo said that Mikki is also confirmed to have a "latent form" of EEHV, but "it is not the same strain that affected" her son. She appears to be behaving normally, the zoo said, as is the institution's other elephant, Punch. Zoo staff will continue to monitor them, the news release said. 

In:
• Louisville
• Elephant
• Kentucky

Kerry Breen

Kerry Breen is a news editor and reporter for CBS News. Her reporting focuses on current events, breaking news and substance use.