U.S. Zookeepers Wary of Herpes Virus Attacking Asian Elephants

ST. LOUIS — Zookeepers here feared the worst when they noticed that Jade, a 2-year-old elephant calf, was acting sluggish this month.

The calf was limping slightly, her appetite was down, and the keepers, wary of a deadly herpes virus prevalent in the country’s Asian elephant population, sent a blood sample to a laboratory for analysis.

“That’s pretty much the first thing we do when we see something amiss with our Asian elephant calves,” said Martha Fischer, curator of mammals at the St. Louis Zoo. “It’s such a mysterious disease, and it has presented itself in so many different ways — anything could be a symptom.”

Veterinarians began monitoring the 1,100-pound calf around the clock. They fed her fluids intravenously and started her on antiviral drugs. Still, her condition worsened.

Her head became swollen at the jaw and forehead, and her tongue, normally bubble-gum pink, became pale and speckled by an intricate pattern of red bruises. Results from the National Elephant Herpesvirus Laboratory at the Smithsonian National Zoo in Washington soon revealed that Jade was fighting a previously unknown strain of the virus.

Researchers say the disease, elephant endotheliotropic herpesvirus, has killed one of five Asian elephant calves born in North American zoos since 2000. It accounts for more than half of all deaths of juvenile elephants in North America, and researchers, working with available tissue samples, estimate that it has killed some 24 elephants since 1983.

Still, the researchers know little about the disease, including how it is transmitted. Nor can they say whether it will remain dormant after its initial assault only to re-emerge, like some herpes viruses in humans.

The disease cannot be detected in the blood unless symptoms are evident, researchers say, and they are unsure what percentage of elephants carry any of the five known strains.

“We’re still trying to figure out the epidemiology,” said Laura Richman, the research associate who heads the Smithsonian laboratory that analyzed Jade’s blood sample. “We’re still trying to figure out how it’s transmitted, and why certain elephants die and others don’t.”

Ms. Richman, who first identified the virus in 1995, says that many mature elephants may carry a latent form of the disease but that calves may be more susceptible because their immune systems are not fully developed.

The virus exists in captive and wild elephant populations, Ms. Richman said, and often affects only one elephant at a time. “There aren’t big outbreaks where you’ll see whole herds of elephants coming down with the virus,” she said. “It’s probably just a matter of which elephants are shedding at what time, but we don’t know — whether it is a secretion of saliva or something else — we just don’t know how it’s transmitted.”

The virus infects the cells that line the body’s blood vessels, causing hemorrhaging. The subsequent vascular collapse often kills its victims within weeks or even days.

Antiviral drugs have been successful in six North American cases, but about twice as many calves have died from the virus even after receiving the drugs, leaving researchers uncertain about how best to fight it.

“We’re not sure that the drugs we’re using are effective against EEHV,” Ms. Fischer said. “We’re not sure what the dose should be. It’s a little bit of a shot in the dark.”

The St. Louis case is shaping up as a trove of information. Jade’s symptoms have largely subsided, Ms. Fischer said, and she appears to be recovering. Blood tests on the zoo’s seven other elephants revealed that another calf, Maliha, carried a very low level of the virus, and researchers say they believe the antiviral drugs she is receiving have stopped its progression.

“I’m not about to say Jade’s out of the woods, but we’re really pleased with her condition,” Ms. Fischer said. “We’re hoping to be able to go back and determine whether the drugs were effective.”

Asian elephants have been listed as an endangered species by the International Union for Conservation of Nature since the mid-1980s. The organization further reports that a combination of ivory poaching and a loss of natural habitat have caused wild elephant numbers to plunge by about 50 percent in the past 75 years to 40,000 to 50,000.

Although experts say the elephant herpesvirus has evolved over millions of years, the dwindling population puts the species at greater risk from the disease.

There are a lot of unanswered questions about the disease, said Mike Keele, deputy director of the Oregon Zoo: “What’s the prevalence of it in the wild population, and how does it affect survivability?”

Mr. Keele said that his zoo’s elephant population had not suffered a herpes outbreak, but that zookeepers were training a 6-month-old male calf to take medications and allow daily inspections of his tongue to guard against an attack.

“There’s no reason why it couldn’t happen here,” Mr. Keele said. “We don’t know how long this virus has been in our population, but no one ever thought to look for it.”

Courtesy of Mike Naughton