A week after Portland’s favorite elephant calf began treatment at the Oregon Zoo for a potentially deadly virus, veterinarians say she remains stable, an encouraging development for a disease that can progress rapidly in young elephants.
Tula-Tu has made it through a week of treatment for elephant endotheliotropic herpesvirus, known as EEHV, a disease that can become life threatening within a few days if it becomes active.
“The calf is responding really well,” zoo spokesperson Kelsey Wallace told The Oregonian/OregonLive on Saturday.
The diagnosis carries particular significance at the Oregon Zoo. Tula-Tu’s older half-sister Lily died suddenly of EEHV at age 6 in 2018.
Since then, advances in early detection, treatment and efforts to develop a vaccine have given veterinarians new tools to deal with the disease.
In February 2025, Tula-Tu became the first live elephant calf born in Portland in more than a decade. She has been regularly tested for the virus that killed her half-sister. And this summer, the now 21-month-old Tula received two doses of a vaccine to protect against the most common strain of elephant endotheliotropic herpesvirus.
Tula’s current infection is from a different strain of the virus than the one the vaccine targeted.
Last Saturday, zoo care staff alerted veterinarians of changes in Tula’s behavior and energy levels. The vet team collected blood samples and found Tula’s white-cell count was low so they started her on antiviral medications.
The next day, testing at the Oregon Veterinary Diagnostic Laboratory at Oregon State University confirmed an elevated viral load of EEHV. To fight the virus, Tula-Tu received plasma transfusions.
The young elephant has remained stable throughout the week, said Dr. Carlos Sanchez, the zoo’s director of animal health. Her current status is encouraging, he said.
“The combination of stable viral loads, normal platelet counts and improving white cell counts suggests a favorable trajectory,” Sanchez said in a statement issued by the zoo. “She’s not out of the woods yet, but these findings provide grounds for cautious optimism.”
The zoo said veterinarians will continue to monitor Tula-Tu’s blood and viral load but have not said how long treatment is expected to continue.
Sanchez said the vaccine Tula received earlier this year may offer some protection against the current virus strain, though researchers do not yet know whether or to what extent that will bear out.
Blood samples from Tula-Tu will also contribute to ongoing research, including a study aimed at better understanding elephants’ response to the vaccine.
EEHV is a latent virus present in nearly all Asian elephants, wild and captive. Most animals become immune to it. But calves are particularly vulnerable as their maternal antibodies wane, typically between ages 1 and 8, before they develop natural immunity.
Scientists have confirmed around 200 EEHV deaths in Asian elephant range countries.
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