February 27, 2009
Herpes Virus Attacks Asian Elephants In US Zoos
A deadly strain of herpes virus common in Asian elephants appears to be increasing in captive elephants at U.S. zoos, the New York Times reported.
The disease, known as elephant endotheliotropic herpesvirus, has killed one of five Asian elephant calves born in North American zoos since 2000, accounting for more than half of all deaths of juvenile elephants in North America.Researchers working with available tissue samples estimate that the virus has killed some 24 elephants since 1983.
So far, little is known about the disease, including how it is transmitted or whether it will remain dormant after its initial assault only to re-emerge, like some herpes viruses in humans.
Jade, a 2-year-old elephant calf at the St. Louis zoo, received blood sample analysis earlier this month after showing signs of sluggishness and loss of appetite.
Martha Fischer, curator of mammals at the St. Louis Zoo, said the elephant herpesvirus is a mysterious disease that presents itself in many different ways.
The baby elephant's condition soon began to worsen and results from the National Elephant Herpesvirus Laboratory at the Smithsonian National Zoo in Washington revealed that it was fighting a previously unknown strain of the virus.
Although the disease cannot be detected in the blood unless symptoms are evident, researchers are unsure how many elephants carry any of the five known strains of the virus.
"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.
She said researchers are still trying to figure out how it's transmitted and why certain elephants die and others don't.
"Many mature elephants can carry a latent form of the disease but calves may be more susceptible because their immune systems are not fully developed," said Richman, who first identified the virus in 1995.
She said the virus exists in both captive and wild elephant populations but 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."
Experts say the virus infects the cells that line the body's blood vessels, causing hemorrhaging; and subsequent vascular collapse often kills its victims within weeks or even days.
Six North American calves have been successfully treated with antiviral drugs, but around a dozen have died from the virus even after receiving the treatment.
"We're not sure that the drugs we're using are effective against EEHV," Fischer said. "We're not sure what the dose should be. It's a little bit of a shot in the dark."
Fischer said Jade's symptoms have largely subsided and she appears to be recovering, but blood tests on the zoo's seven other elephants revealed that another calf, Maliha, carried a very low level of the virus.
However, researchers say they believe the antiviral drugs she is receiving have stopped its progression. "We're hoping to be able to go back and determine whether the drugs were effective," Fischer added.
The International Union for Conservation of Nature has listed Asian elephants as an endangered species since the mid-1980s.
While the elephant herpesvirus has evolved over millions of years, experts say the dwindling population puts the species at a greater risk of contracting the virus.
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