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DEATHS OF ZOO ELEPHANTS EXPLAINED -- NEW VIRUS IDENTIFIED
Researchers at Johns Hopkins in Baltimore and the National Zoo in Washington, D.C., have discovered the cause of death of nearly a dozen young North American zoo elephants -- fatal hemorrhaging from a previously unknown form of herpesvirus that apparently jumped from African elephants to the Asian species.
"This is very troubling because these are endangered species," said Gary Hayward, Ph.D., a Johns Hopkins scientist and co-author of a report published in the Feb. 19 Science. "And also because there may still be carrier African elephants in zoos."
Quick detection and treatment with antiviral drugs is life-saving, he added.
Asian elephants are bred more frequently in captivity than their African cousins, and a sufficient number of young elephants is necessary for bolstering the population, which is dwindling in the wild.
Of 34 Asian elephants born in zoos in the United States and Canada from 1983 to 1996, seven have died from the virus, and two more with incomplete records are suspected to have died from it. The virus appears to be latent in most African elephants, although two of seven African elephants born in North America over the past 15 years have also died from herpesvirus infection. Most of the infected elephants were young.
In their report, the scientists say that the elephant herpesvirus kills by infecting cells that line blood vessels in the heart, liver and other organs. Untreated, the virus soon causes internal bleeding and heart failure. The virus hits suddenly, killing in a few days.
The "index case," or first animal identified as having the virus, was a 16-month-old Asian elephant, Kumari -- the first elephant ever born at the National Zoo. When Kumari died in 1995, her keepers were baffled.
Soon after, Laura Richman, D.V.M., now at The Johns Hopkins School of Medicine, and Richard Montali, D.V.M., of the National Zoo, began investigating the case. When examining tissue samples from Kumari, they found tiny sacks of virus, called inclusion bodies. Using an electron microscope, the researchers saw that the viruses inside the inclusion bodies resembled herpesvirus. DNA analysis confirmed they were indeed dealing with a herpesvirus, although of a type not before identified.
Richman and her colleagues then went through old zoo records and found other elephant deaths in which the symptoms resembled those Kumari had suffered. After analyzing tissue samples from these previous deaths, the researchers confirmed the elephants had died from herpesvirus, leading them to watch out for other cases.
Other elephants were subsequently diagnosed with the virus, one in California in 1996, the second in Missouri in 1997, and the third last year in Florida. Upon hearing about the Missouri elephant, a calf named Chandra, veterinarians at the zoo prescribed the antiviral drug famciclovir. Chandra recovered in a few days. The Florida elephant also recovered after the same treatment.
"We were able to cure these elephants, which is promising. If caught early, the infection appears to be treatable," said Richman.
To see if the virus exists in the wild, the researchers worked with scientists in Zimbabwe and South Africa to collect blood and tissue samples from healthy African elephants. Again they found the virus, with DNA virtually identical to that found in the infected Asian elephants. This work confirmed that the virus exists in, but is nonlethal to, wild African elephants. It was also the piece of the puzzle that suggested how the zoo elephants became infected.
"It's likely that the virus is transmitted from the African to the Asian elephants in the zoos," said Richman. "That's the only way we can account for the same virus being present in both populations." Hayward said a blood test is needed, to identify which elephants may be carrying the virus. He added that separating Asian and African elephants could prevent more deaths.
The research was supported by the National Institutes of Health, the Smithsonian Institution, the Kumari Elephant Conservation Fund, and Friends of the National Zoo.
Relevant Web sites:
Dr. Hayward's home page--
Herpesviruses background --
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