Zoo mobilizes to treat elephant calf for EEHV

Care team's quick intervention offers hope as Tula-Tu battles elephant disease

A team of Oregon Zoo veterinary experts and care specialists has launched a comprehensive treatment plan for Asian elephant Tula-Tu, who is currently battling elephant endotheliotropic herpesvirus, or EEHV, a rapidly progressing disease to which young calves are particularly susceptible.

Care staff alerted veterinarians on Oct. 24 after noticing subtle changes in Tula's behavior and energy levels. The vet team responded immediately, collecting blood samples for rapid diagnostic testing and initiating precautionary treatment even before EEHV was confirmed.

"Early detection is critical," said Dr. Carlos Sanchez, the Oregon Zoo's director of animal health. "We conduct routine blood monitoring in-house, with veterinary technicians trained to recognize elephant-specific blood cells. Right away, they could see Tula's white-cell count was low, so we started her on antiviral medications while we waited for advanced molecular testing to confirm or rule out EEHV."

The next day, the molecular lab at the Oregon Veterinary Diagnostic Laboratory at Oregon State University confirmed an elevated viral load of EEHV, triggering further protocols, including plasma transfusions to fight the virus.

Sanchez says the young elephant has remained stable throughout her treatment, and her current status is encouraging.

"The combination of stable viral loads, normal platelet counts and improving white cell counts suggests a favorable trajectory," Sanchez said. "She's not out of the woods yet, but these findings provide grounds for cautious optimism. Diagnostics and treatment for this disease have advanced so much over the past few years. Every hour of stability brings her one step closer to recovery."

Earlier this year, Tula-Tu became the first elephant on the West Coast to receive an mRNA vaccine aimed at protecting against EEHV-1A, the most common strain of the virus. However, Tula's current infection is from a different, related strain: EEHV-1B. Although EEHV-1B is responsible for fewer reported fatal infections, both variants can cause severe disease in young Asian elephants.

"We do not know whether the EEHV-1A vaccine is protective for the -1B variant," Dr. Sanchez said. "It's possible, but to what degree remains unknown."

Sanchez, who serves as chair of the North American EEHV Advisory Group Research Committee, says EEHV is a latent virus present in nearly all Asian elephants, both wild and in human care. Most elephants develop natural immunity over time, but calves become highly susceptible to the disease as their maternal antibodies decline, typically between the ages of 1 and 8.

Once EEHV becomes active, it can be life-threatening within a few days - as was the case with another of Rose-Tu's calves, Lily, who succumbed to the disease in 2018 shortly before her sixth birthday. But advancements in early detection, vaccines and transfusion protocols have improved survival outcomes significantly.

For nearly 25 years, the Oregon Zoo has contributed funding and elephant blood samples as part of a collaborative international effort to find a vaccine or effective treatment. Collaborating with accredited facilities nationwide, the Oregon Zoo has invested in critical research, testing and monitoring to protect elephants from EEHV.

Sanchez said blood samples from Tula-Tu will help several ongoing studies - including one conducted in partnership with OSU and Baylor to help researchers further understand the vaccine response.

He notes that the virus affects wild elephants as well. Although it is harder to identify and diagnose - and its occurrence in range countries is overshadowed by much more serious threats such as poaching, habitat loss and human-elephant conflict - scientists have confirmed around 200 EEHV deaths in Asian elephant range countries.

"The work we're doing now could play a significant role in protecting future elephant calves from the disease, including those in range countries," Sanchez said. "It's very difficult to study the virus in wild elephants, but zoos can monitor the elephants in their care closely and obtain samples of blood and other fluids."

In 2023, Oregon Zoo veterinary staff worked with Malaysian wildlife officials to set up Sabah's first hematology lab to track signs of EEHV in elephants in the wild and in human care. Zoo veterinary staff provide workshops and support on EEHV diagnostics, monitoring, and response, providing clinical training and awareness for wildlife health practitioners across Southeast Asia.